Today, it is almost certain that global climate change will affect the frequency and severity of extreme meteorological and hydrological events. It is necessary to develop models and methodologies for the better understanding, forecasting, hazard prevention of weather induced extreme events and assessment of disaster risk. This session considers extreme events that lead to disastrous hazards induced by severe weather and climate change. These can, e.g., be tropical or extratropical rain- and wind-storms, hail, tornadoes or lightning events, but also floods, long-lasting periods of drought, periods of extremely high or of extremely low temperatures, etc. Papers are sought which contribute to the understanding of their occurrence (conditions and meteorological development), to assessment of their risk and their future changes, to the ability of models to reproduce them and methods to forecast them or produce early warnings, to proactive planning focusing to damage prevention and damage reduction. Papers are also encouraged that look at complex extreme events produced by combinations of factors that are not extreme by themselves. The session serves as a forum for the interdisciplinary exchange of research approaches and results, involving meteorology, hydrology, hazard management and/or applications like insurance issues.

Public information:

Extreme meteorological and hydrological events induced by severe weather and climate change
Display presentations Monday, 04 May, 08:30–12:30

The presentation of Displays during the chat will be made in the following order:

Severe storms/precipitation (8:30-10:15): D1932, D1933, D1934, D1936, D1938, D1940, D1942, D1943, D1944, D1951, D1952, D1953, D1955, D1956, D1957, D1958, D1960, D1962, D1963 (not presented), D1964, D1965, D1966, D1967, D1969, D1974, D1977, D1982

Floods (10:45-11:05): D1935, D1937, D1939, D1941, D1954, D1959

Droughts and other extreme weather events (11:05-12:30): D1945, D1946, D1947, D1948, D1949, D1950, D1961, D1968 (not presented), D1970, D1971, D1972, D1973 (not presented), D1975, D1976, D1977, D1978, D1979, D1980, D1981, D1983, D1984, D1985

Information (video and text) how to use the chats could be found at https://egu2020.eu/sharing_geoscience_online/how_to_use_the_chats.html

The chairpersons will handle and organize the questions and replies of the presentations, following the above line of presentations. Each author is asked for an introduction (please prepare). Then, we will take questions.

Conveners, co-conveners, and chairpersons of the sessions reserve the right to ban participants showing abusive behaviour or violating EGU's Code of Conduct.

The conveners of the session
Athanasios Loukas
Maria Carmen Llasat
Uwe Ulbrich

Co-organized by AS1/HS13
Convener: Athanasios Loukas | Co-conveners: Maria-Carmen Llasat, Uwe Ulbrich
| Attendance Mon, 04 May, 08:30–12:30 (CEST)

Files for download

Session materials Download all presentations (150MB)

Chat time: Monday, 4 May 2020, 08:30–10:15

Chairperson: A. Loukas, M.C. Llasat, U. Ulbrich
D1932 |
Beata Latos, Thierry Lefort, Maria Flatau, Donaldi Permana, Piotr Flatau, Dariusz Baranowski, Jaka Paski, Erwin Makmur, and Eko Sulystyo

On January 22, 2019 extreme rainfall in the South-Western Sulawesi, Indonesia, triggered a massive, deadly flood, the most devastating one ever reported. This happened during an interaction of a robust Convectively Coupled Kelvin Wave (CCKW) and Equatorial Rossby Wave (ER). Potential causes of a flood include Madden Julian-Oscillation active phase, rainy season with monsoonal flow in the Karimata Strait, positive sea surface temperature anomalies supportive of convection, and synoptic-scale weather systems. All these factors can contribute to extreme rainfall and a flood development. Nonetheless, here we show that in this particular case enhancement of low-level westerlies led to convergence and forced ascend of moist air over orographic features of the south-western Sulawesi. This chain of processes was a result of a propagation of a CCKW, with contribution from an ER. Satellite and radar data analysis, as well as in-situ observations reveal that convergence and strong westerlies in the Java Sea, forced by the CCKW, resulted in the rain events in Jeneberang River Basin and the devastating flood in the city of Makassar.

Additional analysis of 20 years of the flood database together with in situ observations and satellite data support our hypothesis, based on this case study, of a significance of an enhanced westerlies as a precursor of extreme rain events and floods in Makassar, the capital and most populous city in Sulawesi.

How to cite: Latos, B., Lefort, T., Flatau, M., Permana, D., Flatau, P., Baranowski, D., Paski, J., Makmur, E., and Sulystyo, E.: On the role of tropical waves triggering extreme rainfall and flood in Sulawesi, Indonesia: a multi-scale interaction perspective, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-310, https://doi.org/10.5194/egusphere-egu2020-310, 2019

D1933 |
Yiannis Moustakis, Christian J Onof, and Athanasios Paschalis

According to thermodynamics, as the climate gets warmer under climate change the water holding capacity of the air increases at a rate of 7%/oC (Clausius-Clapeyron; CC). This implies that in the absence of severe changes in relative humidity, precipitation extremes (PEx) will increase likewise. Would this relationship prove to be globally robust, then ground temperature predictions could be used as an indicator for predicting future PEx intensification under climate change. This could be a helpful tool, given the well-documented discrepancies of climate models in simulating PEx and the increased confidence in temperature projections. However, studies based on observational and modelled data have revealed contradicting behaviours regarding the scaling rate of PEx with ground temperature. In this study we use hourly data from weather stations (1,461 sites), two convection permitting models and 40 years of climate reanalysis in order to reveal the global scaling pattern of PEx with ground air and dewpoint temperature at fine spatial and temporal scales based on a robust methodology. Our results suggest that a robust ~CC scaling with both air temperature and dew temperature occurs in high- and mid-latitudes. In the tropics and extra-tropics scaling with temperature ranges from negative up to >CC rates, while scaling with dewpoint is strongly positive with >CC values. An investigation of the emerging global pattern reveals that exhibited divergence from CC is linked to the dynamics of deep atmospheric convection in the tropics and extra-tropics. Topography, larger-scale weather patterns and their associated mechanisms shape the scaling pattern in high- and mid- latitudes and seem to disengage ground measurements from activity at the cloud level. In this study we also prove that non-convection permitting models fail to capture the observed behaviour in regions with strong topographic features and/or distinct deep convection. We show that in such regions convection permitting models which capture those features make more reliable estimations.

How to cite: Moustakis, Y., Onof, C. J., and Paschalis, A.: Locality and dynamics shaping the global scaling pattern of hourly precipitation extremes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6106, https://doi.org/10.5194/egusphere-egu2020-6106, 2020

D1934 |
Wenhui Liu, Jidong Wu, Rumei Tang, Mengqi Ye, and Jing Yang

Exploring precipitation threshold from an economic loss perspective is critical for rainstorm and flood disaster risk assessment under climate change. Based on the daily gridded precipitation dataset and direct economic losses (DELs) of rainstorm and flood disasters in the mainland of China, this paper first filtered a relatively reasonable disaster-triggering daily precipitation threshold (DDPT) combination according to the relationship between extreme precipitation days and direct economic loss (DEL) rates at province level and then comprehensively analyzed the spatial landscape of DDPT across China. The results show that (1) the daily precipitation determined by the combination of a 10 mm fixed threshold and 99.3th percentile is recognized as the optimal DDPT of rainstorm and flood disasters, and the correlation coefficient between annual extreme precipitation days and DEL rates reached 0.45 (p < 0.01). (2) The optimal DDPT decreases from southeast (up to 87 mm) to northwest (10 mm) across China, and the DDPTs of 7 out of 31 provinces are lower than 25 mm, while 5 provinces are higher than 50 mm on average. These results suggest that DDPTs exist with large spatial heterogeneity across China, and adopting regional differentiated DDPT is helpful for conducting effective disaster risk analysis.

How to cite: Liu, W., Wu, J., Tang, R., Ye, M., and Yang, J.: Daily Precipitation Threshold for Rainstorm and Flood Disaster in the Mainland of China: An Economic Loss Perspective, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6538, https://doi.org/10.5194/egusphere-egu2020-6538, 2020

D1935 |
Lea Dasallas and Hyunuk An

One of the major consequences of the changing climate is more intense rainfall episodes in climate vulnerable countries, specifically the Philippines. For over the last 10 years, extreme rainfall events had occurred in the country’s capital city, Metro Manila, which resulted to severe urban flooding occurrences.  The intense rainfall combined with the domain’s low elevation, close proximity to large water sheds and river basins, lack of proper urban planning and the un-systematized drainage system had aggravated the flood inundation. Numerous studies were conducted that had used flood models, but none of these had incorporated the effect of water drainage network, which is an integral part of simulating realistic urban flood inundation. Therefore, this research aims to develop an integrated urban inundation model based on digital surface model that assimilates the sewer system applicable for urban domains with complex pipe network. The quadtree shallow water method, a model that provides flexible grid generation that utilizes adaptive quadtree grid and cut method.  The results were analyzed and compared with the validation data obtained from previous extreme rainfall events. The integrated model was also compared to the existing flood inundation methodologies being used for the present flood early warning system. Research results show that present methodology is closer to the validated results as compared to the previous models. The developed model is also perceived to be best applicable for short term flood events. This shows the efficiency of utilizing integrated urban flood modeling in the Philippines, which can be used for extreme and conventional urban flood events in the future.

How to cite: Dasallas, L. and An, H.: Developing an integrated urban inundation flood model for extreme rainfall events with complex sewer system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6608, https://doi.org/10.5194/egusphere-egu2020-6608, 2020

D1936 |
Ying Liu, Yiheng Chen, Otto Chen, Jiao Wang, Lu Zhuo, and Dawei Han

This research evaluates the performance of the Weather Research and Forecasting model (WRF-ARW, version 4.0) in simulating a regional extreme rainfall event over the Alexandria region of Egypt. Different domain configurations, spin-up times and physical schemes are explored to work out appropriate settings for using WRF in the region. Alexandria is an important economic region of the West Nile Delta that faces a growing climate crisis (e.g. rising temperature, rising sea level, increasing flooding) in recent decades, whilst inadequate coverage of in-situ rainfall observations (radars and rain gauges) makes the development of a hydrological early warning system very difficult. Although some researchers have conducted many WRF studies in countries with rich hydrological data, such as the United States and the United Kingdom, there are not many studies in exploring the ability of WRF to reproduce extreme weather events in countries with insufficient data like Egypt. Therefore, we carry out WRF sensitivity studies of an extreme rainfall event (occurred on 04 November 2015) in the Alexandria region to find out the optimal model configurations for Egypt and other similar areas.


In this study, WRF was tested in five scenarios with different types of configurations. The model sensitivity was evaluated for: (1) domain size, (2) number of vertical levels, (3) horizontal resolution (nesting ratio), (4) spin-up times, (5) physical parameterisation schemes (MP, PBL, CU). During the entire screening process, the best configuration identified in each scenario will be adopted as the corresponding configuration in the following scenarios. All simulations used the newly developed ERA5 reanalysis dataset as the forcing data. Model simulations were verified at high temporal and spatial resolutions against the Global Precipitation Measurement data (GPM data). Seven objective verification metrics (POD, FBI, CSI, FAR, RMSE, MBE and SD) were used to calculate the performance of WRF simulations to identify the likely optimal model configurations.


The sensitivity study shows that the rainfall distribution and magnitude are most sensitive to the spin-up time and physical schemes (especially the cumulus convection scheme). It is observed that the improvement of WRF's reproducibility of rainfall intensity may be accompanied by a decrease in the reproducibility of rainfall distribution. The most recommended configurations include three-level nesting (D01 80x80; D02 112x112; D03 88X88), 58 vertical levels, 1:3:3 (31.5, 10.5 and 3.5km) grid ratio, 48h spin-up time, WSM6 microphysics scheme, MYJ planetary boundary layer scheme, and Grell-Freitas cumulus convection scheme. Its hitting rate is 0.818, the false alarm rate is 0.088 and the rainfall mean bias error is -1.639. The knowledge gained in this study provides a useful foundation for developing a flood early warning system by linking WRF with WRF-Hydro.

How to cite: Liu, Y., Chen, Y., Chen, O., Wang, J., Zhuo, L., and Han, D.: Exploration of WRF simulations of extreme rainfall in Egypt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10538, https://doi.org/10.5194/egusphere-egu2020-10538, 2020

D1937 |
Carles Beneyto, José Ángel Aranda, Gerardo Benito, and Félix Francés

An adequate characterization of extreme floods is key for the correct design of the infrastructures and for the flood risk estimation. Traditionally, these studies have been carried out based on the design storm. However, we now know that this approach is uncertain since peak discharges and hydrographs are strongly dependant on the initial conditions of the basin and on the spatio-temporal distribution of the precipitation.
One of the possible solutions that has recently been better welcomed between the scientific community is the continuous simulation. This combination of statistical and deterministic methods consist of the generation of extended synthetic data series of discharges by combining the use of a stochastic weather generator and a hydrological model. Nevertheless, weather generators still need robust data series of observed precipitation in order to perform adequately, especially when trying to capture extremes. To date, however, the length of both available precipitation and discharge records are still not sufficient to guarantee an adequate estimation of extreme discharges, presenting these high uncertainty.
In the present study, the same approach is taken (i.e. continuous simulation). However, in order to deal with the short length of the data records and to improve the estimations of extreme discharges, non-systematic information (i.e. historical and Palaeoflood) is integrated in the methodology, extending the length of the flow records and giving extra information of the higher tail of the distribution function, thus reducing the uncertainty of these estimations.
This methodology was implemented in a Spanish Mediterranean ephemeral catchment, Rambla de la Viuda (Castello, Valencia). The study area comprises an approximate area of 1,500 km2 and presents a mean rainfall of 615 mm, most of them falling within the autumn months (SON) as a consequence of medicanes. The weather generator used was GWEX, which was designed to focus on extremes, and the hydrological model implemented was TETIS, which is a conceptual model and spatially distributed. Both of them were implemented at a daily scale. Non-systematic information was obtained from previous studies, having information at two locations and, therefore, being able to validate the results in more than one point.
The results, in terms of precipitation, showed that weather generators using heavy-tailed marginal distribution functions outperform those using light-tailed distributions (e.g. Exponential or Gamma), especially when extra information is incorporated, as in this study, where regional maxima precipitation studies were integrated for the parametrisation of the weather generator.
With regards to discharges, the incorporation of non-systematic information clearly gave extra information of the higher tail of the distribution function (up to approx. T=600 years in this study), allowing to validate the generated discharges up to larger return periods and, therefore, reducing the uncertainty of the extreme discharge estimations

How to cite: Beneyto, C., Aranda, J. Á., Benito, G., and Francés, F.: Estimation of extreme flooding based on stochastic weather generators supported by the use of non-systematic flood data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16934, https://doi.org/10.5194/egusphere-egu2020-16934, 2020

D1938 |
Kino hoshiba, Keita shimizu, Shiori terai, and Tadashi yamada

In recent years, due to global climate change, flood disaster has become more frequent and intense. Along with this, many researchers in different fields are working on researches to reduce the damage caused by these severe water-related disasters. This study focusses on weather radars, which are mainly used for a countermeasure against flood damage in Japan. Our purpose is to examine the validity of weather radars currently set such as X band multi-parameter radars and C band radars in flood disasters which may cause serious damage in Japan.

The targeted flood disaster is one of the largest water-related disasters which caused severe damages to Japan, the typhoon Hagibis in 2019. It caused floods in more than 140 rivers. We used the observed data from weather radars of Chikuma and Abukuma river which are severely damaged in this disaster. Also, the Tama River in the Tokyo metropolitan area was flooded because of the heavy rainfall caused by Hagibis. we compared the accuracy of the multi-parameter radar and the single-parameter radar. thus, the issues of the current weather radar were extracted.

As a result, the accumulated rainfall of the single-parameter radars was larger than that of the multi-parameter radars. This may cause by the fact that radio wave of the multi-parameter radars will get attenuated when it passesthrough areas with strong rainfall so that it is difficult to observe some area if there is strong rainfall area between the radar and targeted area. In addition, the values observed by multi-parameter weather radars are fitted with the values by the ground rain gauges.

In conclusion, it was found that the multi-parameter weather radars have better accuracy of precipitation observation than that of the single parameter weather radars. Furthermore, it is necessary to consider the optimal position of multi-parameter weather radars to improve accuracy of the observation.

How to cite: hoshiba, K., shimizu, K., terai, S., and yamada, T.: Comparison of observed rainfall characteristics by using Multi-Parameter Weather Radars and Single parameter Weather Radars for the typhoon Hagibis in 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21169, https://doi.org/10.5194/egusphere-egu2020-21169, 2020

D1939 |
Arnau Amengual, Jorge Lorenzo-Lacruz, Celso Garcia, Enrique Morán Tejeda, Víctor Homar, Aina Maimó-Far, Alejandro Hermoso, Climent Ramis, and Romu Romero

An extraordinary convective rainfall event –unforeseen by most numerical weather prediction models– led to a devastating flash flood in the town of Sant Llorenç des Cardassar, eastern Mallorca, on 9th October 2018. Four people died inside the village, while the total death toll was of 13 and economic damages amounted to 91 M€. The observed flooded extension inside the town by the Copernicus Emergency Management Service –based on Sentinel-1 imagery– far exceeded the extension for a 500-year return period flood. This extreme event has been reconstructed by implementing an integrated flood modelling approach over the semi-arid and small-sized Ses Planes basin up to Sant Llorenç (23.4 km²). This procedure is based on three components: (i) generation of high spatial and temporal resolution radar-derived precipitation estimates; (ii) modelling of the hydrologic response based on post-flood peak discharge estimates; and (iii) hydraulic simulation and mapping of the affected areas based on high water marks. Radar-derived rainfall estimates and the simulated flooding extent and water depths highly correlate with observations. The hydraulic simulation has revealed that water reached a depth of 3 m at some points inside Sant Llorenç and that water velocity greatly increased at bridges’ locations close to the town centre. Even if the catastrophic flash flood was not a debris flow, the flood bore eroded enough material to change channel geomorphology. This study also highlights how the concurrence of the very low predictability of this type of extreme convective rainfall events and the very short hydrological response times typical of small Mediterranean catchments still challenges the implementation of early warning systems, which effectively reduce people’s exposure to flash flood risk in the region.

How to cite: Amengual, A., Lorenzo-Lacruz, J., Garcia, C., Morán Tejeda, E., Homar, V., Maimó-Far, A., Hermoso, A., Ramis, C., and Romero, R.: A forensic hydrometeorological and geomorphological reconstruction of the catastrophic flash flood occurred in Mallorca (Spain) on October 9th, 2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3881, https://doi.org/10.5194/egusphere-egu2020-3881, 2020

D1940 |
Yejia Qiang and Limin Zhang

Under global warming, extreme meteorological events may increase in some regions in terms of both frequency and intensity in the future. Low-lying coastal areas may face the threat both from intensive rainfall and high sea level caused by sea level rise and enhanced storm surge. The Pearl River Delta (PRD) is one of the economic centers of China and is very densely populated. However, PRD is one of the most storm surge-exposed and flood-exposed urban areas in the world. This paper aims to assess the possible impacts of extreme sea level and rainfall on the costal urban areas in PRD. Frequency analysis on historical data of storm surge level and rainfall intensity is conducted, and several scenarios of combination of different magnitudes of the two meteorological events are designed. The trend of observed local sea level and possible land subsidence are also considered. The scenarios are used as inputs for a flood routing model to evaluate the combined impacts of the two meteorological events. Flood maps are produced for each scenario and the infrastructures potentially affected such as buildings and roads can be identified. The results can help identify critical areas prone to hazards under extreme cases and are meaningful for designing hazard prevention measurements.

How to cite: Qiang, Y. and Zhang, L.: Evaluation of the impact of extreme storm surge and rainfall in coastal areas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4985, https://doi.org/10.5194/egusphere-egu2020-4985, 2020

D1941 |
Alejandro Hermoso, Victor Homar, and Arnau Amengual

The Mediterranean region is frequently affected by heavy precipitation and flash flooding during the extended warm season. A precise meteorological forecast of socially relevant aspects of these phenomena such as location, timing and intensity is crucial to prevent personal and material losses. However, forecasting these aspects becomes extremely challenging due to small-scale processes involved in the triggering, development and subsequent evolution of convective systems.


On 12 and 13 September 2019 widespread flash flooding caused devastating effects across Murcia and Valencia, eastern Spain. Seven fatalities were reported, hundreds of homes were flooded and economic losses were estimated at 200 M€. The performance of various ensemble generation strategies for short-range convection-permitting ensemble prediction systems (EPS) are evaluated for this episode. Different sources of error are coped by the implemented ensemble generation approaches.  Uncertainty in the initial and lateral boundary conditions uncertainty is sampled in two ways: (i) the dynamical downscaling of the ECMWF global EPS and, (ii) a new tailored breeding technique that accounts for perturbations across the multiple scales of interest for short-range forecasting. Additionally, errors in mesoscale model formulation are encompassed by combining different parameterization schemes and stochastic physics.


This study contributes to the identification of the most relevant sources of uncertainty hampering an accurate spatial and temporal forecasting of heavy precipitation resulting in flash flooding over the Spanish Mediterranean region. These cutting-edge EPS can contribute to implement more reliable and effective hydrometeorological prediction chains with lead times up to 24 h, providing a valuable support to civil protection and emergency management authorities.

How to cite: Hermoso, A., Homar, V., and Amengual, A.: Ensemble generation strategies for the short-range forecast of flash floods: the 12-13 September 2019 event in Eastern Spain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10453, https://doi.org/10.5194/egusphere-egu2020-10453, 2020

D1942 |
Kirien Whan, Jana Sillmann, Nathalie Schaller, and Rein Haarsma

Atmospheric rivers (AR) are associated with flooding events in Norway, like the flood that impacted Flåm in 2014. We assess trends in Norwegian AR characteristics, and the influence of AR variability on extreme precipitation in Norway. After evaluating the global climate model, EC-Earth, compared to the ERA-Interim reanalysis, we show that ARs increase in both intensity and frequency by the end of the century. In two regions on the west coast, the majority of winter precipitation maxima are associated with AR events (> 80% of cases). A non-stationary extreme value analysis indicates that the magnitude of extreme precipitation events in these regions is associated with AR intensity. Indeed, the 1-in-20 year extreme event is 17% larger when the AR-intensity is high, compared to when it is low. Finally, we find that the region mean temperature during winter AR events increases in the future. In the future, when the climate is generally warmer, AR days will tend to make landfall when the temperature is above the freezing point. The partitioning of more precipitation as rain, rather than snow, can have severe impacts on flooding and water resource management in Norway.

How to cite: Whan, K., Sillmann, J., Schaller, N., and Haarsma, R.: Future changes in atmospheric rivers and extreme precipitation in Norway, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18594, https://doi.org/10.5194/egusphere-egu2020-18594, 2020

D1943 |
Giuseppe Cipolla, Antonio Francipane, and Leonardo Noto

Since the impacts of climate change on the environment have been constantly rising over the last decades, scientists have paid much attention to understanding the effects of this phenomenon. Climate change leads to different kinds of extremes, such as heavy rainfall events, characterized by short duration and high intensity, and drought, which can cause the problem of water scarcity over a certain area. These types of extreme events cause several damages for the affected areas since they can result in loss of human lives and economic damages. In particular, heavy rainfall events, which are often associated with convective precipitation because of their characteristics, may result in flash floods, especially when they hit small catchments with low times of concentration, thus causing economic damages and, more relevantly, human lives losses.

The increasing occurrence of heavy rainfall events in many areas of Europe, also in Italy, over the last few years, has contributed to raising the importance of understanding which factors could be recognized as drivers of these events. In this perspective, it is possible to identify in atmospheric circulation one of the causes of severe rainfall events occurrence since some air fluxes, generated from certain schemes of atmospheric circulation, could lead to the accumulation of moisture within a certain volume of the atmosphere, hence to the occurrence of rainfall.

Since even the Sicily (Italy) has been experimenting heavy rainfall events and consequent flash floods and urban floods in the last years, this work aims to find out a relationship between some weather circulation patterns, developed by the UK Met Office, and the rainfall Annual MAXima (AMAX) for the Sicily, recorded by the rain gauge network of Autorità di Bacino - Regione Siciliana. The possible connection between AMAX and WPs has been investigated in order to define some specific schemes of atmospheric circulation that are responsible for leading to the occurrence of AMAX in Sicily. In order to do this, a database containing the AMAX of all the available gauges for the Sicily has been used. A distinction between AMAX occurred in summer and winter season and their related WPs has been performed as well, with the goal to understand the possible influence of WPs on the summer and winter AMAX. Furthermore, in order to distinguish convective from stratiform AMAX, some analyses on reanalysis data, namely the CAPE and the Vertical Integral of Divergence of Moisture Flux (VIDMF), have been done.

How to cite: Cipolla, G., Francipane, A., and Noto, L.: Weather circulation patterns as precursor of heavy rainfall events: an application to Sicily, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19853, https://doi.org/10.5194/egusphere-egu2020-19853, 2020

D1944 |
| Highlight
Md. Humayain Kabir and Gottfried Kirchengast

The expected intensification of short duration extreme convective precipitation events (SDECPEs) under climate change likely leads to an increase of flash floods and landslides in vulnerable catchments such as the Styrian Raab catchment in the southeastern Alpine forelands of Austria. These extreme events may have strongly adverse effects on different sectors such as public infrastructure, households, and agriculture. Therefore, a clear understanding of SDECPEs is crucial to avoid severe damage risks.

In this work we aim to assess in this context the fingerprint of climate warming in SDECPE’s sub-hourly and hourly rainfall intensities in the southeastern alpine forelands in summertime from data over 1961-2019 within a southeast Austria focus region. We use high-resolution precipitation and temperature time series, and auxiliary data, from 20 gauges of the Austrian weather service (ZAMG) and the Austrian hydrographic service (AHYD) over 1961 to 2019 and additionally from the dense WegenerNet network of around 150 stations in southeast Austria, available over 2007 to 2019. Complementary synoptic data over the greater Alpine region, mainly from the European Reanalysis ERA5, help in convective-event weather typing and interpretation. Weather typing through principal component and cluster analysis as well as artificial intelligence methods and joint station analyses aid to assess the SDECPE changes.

It is found that extreme summertime precipitation in this region is frequently of short-term convective type and its intensity increased. According to previous work on temperature-precipitation scaling (Schroeer and Kirchengast, Clim.Dyn., doi:10.1007/s00382-017-3857-9, 2018), sub-hourly and hourly SDECPE intensities scale at super-CC rates in the region (about 9–14 % per °C) and we will report preliminary results on the rainfall intensification over the long-term time horizon from 1960 to present.


How to cite: Kabir, Md. H. and Kirchengast, G.: Short-duration extreme convective precipitation in the southeastern Alpine forelands of Austria under climate warming, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22016, https://doi.org/10.5194/egusphere-egu2020-22016, 2020

D1945 |
Antonio Ricchi, Vincenzo mazzarella, Lorenzo Sangelantoni, Gianluca Redaelli, and Rossella Ferretti

A severe weather events hit Italy on July 9-10, 2019 causing heavy damages by the falling of large-size hail. A trough from Northern Europe affected Italy and the Balkans advecting cold air on the Adriatic Sea. The intrusion of relatively cold and dry air on the Adriatic Sea, in a first stage through the "Bora jets" generated by the Dinaric Alps gave rise to a frontal structure on the ground, which rapidly moved from North to South Adriatic. The large thermal gradient (also with the sea surface), the interaction with the complex orography and the coastal zone, generated several storm structures along the eastern Italian coast.  In particular, on 10 July 2019 between 8UTC and 12UTC a deep convective cell (probably a supercell) developed along the coast North of the city of Pescara, producing intense rainfall (accumulated rainfall reaching 130 mm/3h) and a violent hailstorm with hailstones larger than 10 cm in diameter. The storm quickly moved southward, evolving into a complex multicellular structure clearly visible by observing radar data.  In this work the frontal dynamics and the genesis of the storm cell are investigated using the numerical model WRF (Weather Research and Forecasting system). Numerical experiments are carried out using a 1 km grid on Central Italy, initialized using the ECMWF dataset and the Sea Surface Temperature (SST) taken by MFS-CMEMS Copernicus dataset. The sensitivity study investigated both the impact of the initial conditions, the quality and the anomaly of the SST on the Adriatic basin in those days. Furthermore, in order to quantify the importance of the use of different microphysics, Planetary boundary Layer (PBL) and radiative schemes, several experiments are performed. The role of orography in the development and location of the convective cell is also investigated. Preliminary results show that initialization and SST played a fundamental role. In particular, the initialization several hours before the event, coupled with a detailed SST allows to correctly reproduce the atmospheric fields. The microphysics scheme turned out to play a key role for this event by showing a significant greater impact than the PBL, in terms of frontal genesis on both the synoptic and local scale.

How to cite: Ricchi, A., mazzarella, V., Sangelantoni, L., Redaelli, G., and Ferretti, R.: Investigating triggering mechanisms for the large hailstorm event of July 10th, 2019 on the Adriatic Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17847, https://doi.org/10.5194/egusphere-egu2020-17847, 2020

D1946 |
Paul Prikryl, Vojto Rušin, Pavel Šťastný, Maroš Turňa, and Martina Zeleňáková

Tropical and extratropical cyclones can intensify into the most destructive weather systems that have significant societal and economic impacts. Rapid intensification of such weather systems has been examined in the context of solar wind coupling to the magnetosphere-ionosphere-atmosphere (MIA) system. It has been shown [1,2] that explosive extratropical cyclones and rapid intensification of tropical cyclones tend to follow arrivals of high-speed solar wind when the MIA coupling is strongest. The coupling generates atmospheric gravity waves (AGWs) that propagate from the high-latitude lower thermosphere both upward and downward [3,4]. In the upper atmosphere, AGWs are observed as traveling ionospheric disturbances. In the lower atmosphere, they can reach the troposphere and be ducted [4] to low latitudes. Despite significantly reduced wave amplitude, but subject to amplification upon over-reflection in the upper troposphere, these AGWs can trigger/release moist instabilities leading to convection and latent heat release, which is the energy driving the storms. The release of conditional symmetric instability is known to initiate slantwise convection producing rain/snow bands in extratropical cyclones. Severe weather, including severe winter storms, heavy snowfall and rainfall events, have been examined in the context of MIA coupling [5]. The results indicate a tendency of significant weather events, particularly if caused by low pressure systems in winter, to follow arrivals of solar wind high-speed streams from coronal holes. In the present paper we review the published results and provide further evidence to support them. This includes the occurrence of heavy rainfall events and flash floods, as well as the rapid intensification of recent hurricanes and typhoons, with the goal to identify sources of AGWs at high latitudes that may play a role in triggering convective bursts potentially leading to such events.

[1] Prikryl P., et al., J. Atmos. Sol.-Terr. Phys., 149, 219–231, 2016.

[2] Prikryl P., et al., J. Atmos. Sol.-Terr. Phys., 183, 36–60, 2019.

[3] Prikryl P., et al., Ann. Geophys., 23, 401–417, 2005.

[4] Mayr H.G., et al., J. Geophys. Res., 89, 10929–10959, 1984.

[5] Prikryl P., et al., J. Atmos. Sol.-Terr. Phys., 171, 94–110, 2018.

How to cite: Prikryl, P., Rušin, V., Šťastný, P., Turňa, M., and Zeleňáková, M.: Severe weather in the context of solar wind coupling to the magnetosphere-ionosphere-atmosphere system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4968, https://doi.org/10.5194/egusphere-egu2020-4968, 2020

D1947 |
Ricardo Trigo, Pedro Sousa, David Barriopedro, Ricardo García-Herrera, Carlos Ordóñez, and Pedro Soares

In the current study, we analyzed the two outstanding heatwaves (HWs) that affected Europe in summer 2019. The events occurred in late June and late July and were record-breaking, although peak temperatures were observed in distinct areas. During the June HW the highest temperatures were recorded in SE France, when the country registered for the first time temperatures above 45ºC. The July HW made thermometers cross the psychological barrier of 40ºC for the first time in Belgium and the Netherlands, breaking all-time records in widespread areas of Central Europe.

We detected that a subtropical ridge fostering warm advection from lower latitudes was a common feature for both HWs. However, we have also found distinct mechanisms shaping the two HWs. While the June HW was predominantly characterized by the intrusion of a vertically homogenous air mass of Saharan origin, surface processes and upward transport of sensible heat were pivotal for the July HW. Our results suggest that the intensity and extension of the June HW contributed to soil desiccation, which together with the persistence of dry and clear sky conditions during early July led to an amplification of the surface temperature anomalies during the late July HW. This is supported by a flow analogue exercise, showing amplified surface heating for flow analogues of the July HW when they are preceded by short-term dry soil moisture conditions, like those caused by the June HW. In turn, we show that, in agreement with the long-term regional warming, soil desiccation during the June 2019 event was larger than it would have been in the recent past (assessing 1984-2018 versus 1950-1983). Finally, we compared the spatio-temporal distribution of summer temperature for 2019 and the previous record-breaking summer 2003. Results show that an outstanding warming fingerprint (circa +1.5ºC in summer daily maximum temperatures averaged over Europe) has been superimposed on the relatively larger magnitude of the August 2003 HW (with respect to the climatology at that time), thus explaining the exceptionality of the record-breaking values observed in 2019.

This work was supported by national funds through FCT (Fundação para a Ciência e a Tecnologia, Portugal) under project IMPECAF (PTDC/CTA-CLI/28902/2017).

How to cite: Trigo, R., Sousa, P., Barriopedro, D., García-Herrera, R., Ordóñez, C., and Soares, P.: The outstanding 2019 Heatwaves in Central Europe – driving mechanisms and soil-atmosphere feedbacks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5601, https://doi.org/10.5194/egusphere-egu2020-5601, 2020

D1948 |
Antoine Guion, Solène Turquety, Jan Polcher, Romain Pennel, and Lluis Fita

In line with what is expected in a context of global warming, droughts and heatwaves have increased both in frequency and intensity over the last century. Severe wildfires and vegetation depletion can result from those extreme weather events with considerable economic, social and environmental damages.

For the development of mitigation and adaptation strategies, there is a need for exhaustive vulnerability assessments, including the impacts of droughts and heatwaves on the Mediterranean environment.

If heatwave characteristics are well documented, similar studies about droughts are partial. Most of them are focused on meteorological droughts while agronomical ones are more complex to identify.


Using a coupled land surface–atmosphere regional model (ORCHIDEE-WRF) with the integration of plant phenology, we present an analysis of droughts and heatwaves occurring in the Western Mediterranean over the last 40 years. These extreme events are identified using two complementary methods: the Percentile Limit Anomalies (PLA) and the Standardized Precipitation Evapotranspiration Index (SPEI).

Impact assessment analysis show significant and dominant effect of droughts on plant phenology during summer. Evaluated using the Leaf Area Index (LAI), plant depletion can reach more than 50%. Response to drought depends on the vegetation type (long vs short root system) and biome (temperate vs semi-arid).

The impact of these extreme events on fire risk will be presented based on calculations of the wildfire meteorological risk (Fire Weather Index) and an analysis of the fire activity observed by the MODIS satellite instrument. We show that, even if extreme high temperature is the dominant cause, drought contributes to an increase of risk. Simultaneous heatwaves and droughts are the worst environmental conditions. The observed burned area can be ±4 times greater than during non-extreme conditions and the fire duration ±0.25 times longer.

How to cite: Guion, A., Turquety, S., Polcher, J., Pennel, R., and Fita, L.: Identification of droughts and heatwaves in the Western Mediterranean, variability and impacts on vegetation and wildfires using the coupled ORCHIDEE-WRF regional model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7719, https://doi.org/10.5194/egusphere-egu2020-7719, 2020

D1949 |
Diana Francis, Noor AlShamsi, Juan Cuesta, Ayse Gokcen Isik, and Cihan Dundar

The first 10 days of September 2015 were marked by an intense dust activity over the Middle East and the Arabian Peninsula. This study examines the atmospheric conditions at the origin of the large dust storms during this period. We particularly investigate the atmospheric dynamics leading to the development of a large dry cyclone over Iraq on 31 August 2015 which in turn generated an intense dust storm that affected most of the countries around the Arabian Gulf and lasted for 5 days. We found that the cyclone developed over Northwest Iraq as a transfer to low levels of a cut-off low which had formed two days earlier at upper levels over Turkey. Large dust loads exceeding 250 tons were emitted and moved southeast in a cyclonic shape toward the Arabian sea. The second large dust storm on 6-8 September 2015 occurred over Syria and affected all the coastal countries on the eastern side of the Mediterranean Sea. It was associated with the occurrence of a series of density currents over northeast Syria emanating from deep convection over the mountainous border between Syria and Turkey. The unusual development of deep convection over this area was associated with a blocking high and interaction with orography. Both the cut-off high and the cut-off low occurred during a period characterized by a meandering polar jet and an enhanced subtropical jet causing unstable weather over mid-latitudes which in turn led to highly polluted atmosphere by natural dust in the affected countries.
Keywords: Cut-off low; cut-off high; upper-level trough; density current; cyclone; evaporation cooling; desert areas; dust storms; polar jet; subtropical jet.

How to cite: Francis, D., AlShamsi, N., Cuesta, J., Gokcen Isik, A., and Dundar, C.: Cyclogenesis and density currents in the Middle East and the associated dust activity in September 2015, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12738, https://doi.org/10.5194/egusphere-egu2020-12738, 2020

D1950 |
Hans de Moel, Lucas Wouters, Maaike Boon, Demi van Putten, Bram Van 't Veen, and Elco Koks

Convective storms that produce large hail are among the most damaging natural hazards and globally losses due to these events are increasing. To evaluate and quantify the potential risk associated with these storms, hail climatologies are created from historical records. Unfortunately, a comprehensive analysis of the Netherlands does not exist.

The aim of this study is to create a hail climatology of the Netherlands and report on spatial and temporal hail risk by combining two approaches. The first approach relies on written documents containing information on historic events collected from Weerspiegel-magazine and the European Severe Weather Database (ESWD), from the time period 1974-2019. The second approach utilizes radar-data from the time period 2008-2019 and implements a radar-based Hail Detection Algorithm (HDA) to estimate hailstone sizes.

Using these sources of hail observations, return periods are estimated for hail storms with various hail sizes in the Netherlands. Moreover, spatial differences within the Netherlands are explored based on both the written documents as well as the radar-based observations. Using this climatology, probabilities of being hit by hail with a certain size are calculated, differentiated by province. Such probabilities are of direct use for developing and evaluating risk management strategies for both the public (municipalities) and private sector (such as insurance). This becomes evident when looking, for instance, at solar panels, which serve an important role in the transition towards climate-neutral urban areas, but are also vulnerable to an (increasing) hail risk.

How to cite: de Moel, H., Wouters, L., Boon, M., van Putten, D., Van 't Veen, B., and Koks, E.: Hail climatology and impacts for the Netherlands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19880, https://doi.org/10.5194/egusphere-egu2020-19880, 2020

D1951 |
Roberto Ingrosso, Piero Lionello, Mario Marcello Miglietta, and Gianfausto Salvadori

57 tornadoes with intensity Enhanced Fujita Scale 2 or larger that occurred in Italy in the period 2000–2018 are analysed in order to investigate the way two meteorological parameters, namely Wind Shear, calculated in 0-1 km and 0-6 km layers, and CAPE, affect their development. For this purpose, a statistical analysis, by means of homogeneity tests, conditional probabilities and a multivariate analysis via copulas is performed, using two different re-analysis datasets (ERA-Interim and ERA-5). The study indicates that: (a) tornadoes occur mostly in correspondence with positive anomalies of both variables; (b) probability of occurrence is correlated with WS, and (c) is maximum when either WS or CAPE are large. Also, the probability does not increase significantly with CAPE, although sufficiently large values are needed for tornado occurrence. These results are similar for both re-analyses we used and suggest that the selected parameters are reliable precursors for Italian tornadoes.

How to cite: Ingrosso, R., Lionello, P., Miglietta, M. M., and Salvadori, G.: A probability model of three potential precursors during tornado occurrences: the Italian case., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5474, https://doi.org/10.5194/egusphere-egu2020-5474, 2020

D1952 |
Gregor C. Leckebusch and Kelvin S. Ng

Understanding high impact land-affecting tropical cyclones (TCs) is of crucial importance due to its potential to cause high socioeconomic damages and losses to many coastal areas.  However, due to the rarity of extreme severe TCs and the lack of persistent long-term meteorological observations, it is difficult to construct a robust risk assessment of high impact TCs based solely on historical records.  This poses a problem from the disaster risk reduction (DDR) perspective, e.g. for the development of financial instruments, as the estimate of occurrence probabilities above damage relevant thresholds remains highly uncertain. In this study, we present an overview and first results of our current project – INtegrated threshold development for PArametric Insurance Solutions (INPAIS), which demonstrates a way forward to improve expected occurrence probabilities of those events for the Western North Pacific (WNP).

We introduce a new approach to construct a TC event set for the WNP based on multi-model ensemble global forecasts – the THORPEX Interactive Grand Global Ensemble (TIGGE) dataset in combination with an impact-based tracking algorithm for Typhoons. This event set contains physically consistent events, which were forecasted but not necessarily realised in the observed past. With respect to the physical characteristics of these forecasted, but not realised events, they are not distinguishable from real TC events. This approach will allow to analyse data equivalent to more than 10,000 years.

In addition to the TC-related wind information, the TC-related precipitation, which is physically consistent with the associated TC, can also be obtained. This provides an opportunity to analyse the compound TC risk (wind and precipitation) using physically consistent data for the WNP. We further demonstrate how this information can be used to improve existing financial instrument for DRR, e.g. parametric insurance solution which is offered by many re-insurance companies, such that resilience and post-disaster recovery speed of society can be improved.

How to cite: Leckebusch, G. C. and Ng, K. S.: Assessing Typhoon Risk Using Multi-model Ensemble Forecasts for Disaster Risk Reduction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8531, https://doi.org/10.5194/egusphere-egu2020-8531, 2020

D1953 |
Asiya Badarunnisa Sainudeen and Prasanta Sanyal

Indian subcontinent receives precipitation from the southwest monsoon, northeast monsoon, and western disturbances. Unlike southwest and northeast monsoon, precipitation by western disturbances is less studied in terms of understanding its forcing factors and future behavior. Synoptic weather phenomena that originate in temperate north-Atlantic and the Mediterranean sea are primarily responsible for the moisture convergence towards the Indian landmass through an eastward movement and cause Western Disturbance Precipitation (WDP) in Turkey, Iran, Pakistan, Afghanistan, and northwestern India during winter (December-March). Long term (116 years) WDP shows an increasing trend over most of the regions. To understand the forcing factors in WDP, a long term pressure gradient between the Indian landmass and northern Atlantic has been calculated. This pressure gradient also shows an increasing trend, thereby suggesting its direct influence on WDP. This influence is observed not only in the long term WDP but for each winter month as well. Previous studies showed the impact of Pacific ocean sea surface temperature (SST)  on the modulation of northern Atlantic ocean SST and surface pressure. However, no quantitative estimation on the relation of Pacific SST with WDP is known. Here, an attempt has been made to understand the role of Pacific SST in the long term trend of WDP.

Changes in SST and convection in the tropical Pacific region determines the interannual variability as well as seasonal climate forecasting all over the world by modulating the air-sea coupling and sea level pressure. Therefore, the potential impact of Pacific SST on WDP has been tested, and a significant correlation between them has been observed. To understand the causal factors behind such relation, statistical analysis like Pearson's correlation analysis was performed by taking the SST of the Nino 3.4 region with the surface pressure of the northern Atlantic and Indian subcontinent. This analysis gave a significant positive correlation (R=0.24) among NINO 3.4 SST and surface pressure over the northern Atlantic and negative correlation (R=-0.28) between NINO 3.4 SST and surface pressure of the Indian region. From this analysis, it is inferred that the Pacific warm pool primarily drives the lower and higher surface pressure over Indian landmass and northern Atlantic, respectively, by modulating the local meridional and zonal circulation, which further dictates WDP.


Dimri, A. P., et al. "Western disturbances: a review."Reviews of Geophysics 53.2 (2015): 225-246.    

Enfield, DAVID B., and ALBERTO M. Mestas-Nuñez. "Global modes of ENSO and non-ENSO sea surface temperature variability and their associations with climate."El-Niño and the Southern Oscillation: multiscale variability and global and regional impacts (2000): 89-112.


How to cite: Badarunnisa Sainudeen, A. and Sanyal, P.: Impact of surface warming over Equatorial Pacific ocean in western disturbances precipitation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-633, https://doi.org/10.5194/egusphere-egu2020-633, 2019

D1954 |
Alexandra Fedorova, Nataliia Nesterova, Olga Makarieva, and Andrey Shikhov

In June 2019, the extreme flash flood was formed on the rivers of the Irkutsk region originating from the East Sayan mountains. This flood became the most hazardous one in the region in 80 years history of observations.

The greatest rise in water level was recorded at the Iya River in the town of Tulun (more than 9 m in three days). The recorded water level was more than 5 m above the dangerous mark of 850 cm and more than 2.5 m above the historical maximum water level which was observed in 1984.

The flood led to the catastrophic inundation of the town of Tulun, 25 people died and 8 went missing. According to preliminary assessment, economic damage from the flood in 2019 amounted up to half a billion Euro.

Among the reasons for the extreme flood in June 2019 that are discussed are heavy rains as a result of climate change, melting of snow and glaciers in the mountains of the East Sayan, deforestation of river basins due to clearings and fires, etc.

The aim of the study was to analyze the factors that led to the formation of a catastrophic flood in June 2019, as well as estimate the maximum discharge of at the Iya River. For calculations, the deterministic distributed hydrological model Hydrograph was applied. We used the observed data of meteorological stations and the forecast values ​​of the global weather forecast model ICON. The estimated discharge has exceeded previously observed one by about 50%.

The results of the study have shown that recent flood damage was caused mainly by unprepared infrastructure. The safety dam which was built in the town of Tulun just ten years ago was 2 meters lower than maximum observed water level in 2019. This case and many other cases in Russia suggest that the flood frequency analysis of even long-term historical data may mislead design engineers to significantly underestimate the probability and magnitude of flash floods. There are the evidences of observed precipitation regime transformations which directly contribute to the formation of dangerous hydrological phenomena. The details of the study for the Irkutsk region will be presented.

How to cite: Fedorova, A., Nesterova, N., Makarieva, O., and Shikhov, A.: May long-term historical hydrological data be misleading for flood frequency analysis in current conditions of climate change?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1140, https://doi.org/10.5194/egusphere-egu2020-1140, 2019

D1955 |
Xi Lu

This study evaluates 32 climate models from CMIP5 compared with a daily gridded
observation dataset of extreme precipitation indices including total extreme precipitation (R95p),
maximum consecutive five days of precipitation (RX5day) and wet days larger than 10 mm of
precipitation (R10mm) over Northern China during the historical period (1986–2005). Results show
the majority models have good performance on spatial distribution but overestimate the amplitude of
precipitation over Northern China. Most models can also capture interannual variation of R95p and
RX5d, but with poor simulations on R10mm. Considering both spatial and temporal factors, the best
multi-model ensemble (Group 1) has been selected and improved by 42%, 34%, and 37% for R95p,
RX5d, and R10mm, respectively. Projection of extreme precipitation indicates that the fastest-rising
region is in Northwest China due to the enhanced rainfall intensity. However, the uncertainty
analysis shows the increase of extreme rainfall over Northwest China has a low confidence level.
The projection of increasing extreme rainfall over Northeast China from Group 1 due to the longer
extreme rainfall days is more credible. The weak subtropical high and southwest winds from Arabian
Sea lead to the low wet biases from Group 1 and the cyclonic anomalies over Northeast China, which
result in more extreme precipitation.

How to cite: Lu, X.: Evaluation and Projection of Extreme Precipitation over Northern China in CMIP5 Models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1458, https://doi.org/10.5194/egusphere-egu2020-1458, 2019

D1956 |
Rui Wang

    In this work, the relationship between daily extreme precipitation and temperature is investigated by using rain gauge precipitation data and corresponding the Integrated Global Radiosonde Archive over eastern China during 1998-2012. Eventually, 14 stations are selected to explore the relationship in eastern China (MEC) and southeastern China (SEC). The result shows that daily extreme precipitation intensity increases approximately 7% when near surface temperature increases 1 °C in MEC and SEC, which generally follows Clausius–Clapeyron (CC) rate (CC rate describes the increasing rate of water vapor with temperature). Moreover, the regression slopes for the logarithmic daily extreme precipitation intensity and near surface temperature range from 3% °C-1 to 9% °C-1 at the selected stations in MEC and SEC. However, extreme precipitation intensity decreases with near surface temperature when the temperature is higher than 25 °C. That is, the increase of extreme precipitation with near surface temperature performances single peak structure in MEC and SEC. The variation of extreme precipitation and near surface dew point temperature shows the similar pattern in MEC and SEC (The transition dew point temperature is also about 25 °C). Therefore, it could be deduced that extreme precipitation intensity does not always increase with climate warming in MEC and SEC. In addition, precipitable water, which corresponds to extreme precipitation event, increases with near surface temperature at CC rate. It is found that the increase rate of precipitable water with temperature is closer to CC rate than that of extreme precipitation.

How to cite: Wang, R.: Evaluation of the relationship between daily extreme precipitation and temperature over Eastern China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2297, https://doi.org/10.5194/egusphere-egu2020-2297, 2020

D1957 |
Jou Ping Hou, Li Zhen Su, and Yi Hao Liao

From May to June in Southeast Asia, the cold high pressure on the mainland gradually weakens and the Pacific high pressure gradually increases. These two cold and warm pressure systems will form confrontations near Taiwan and South China. The stable "front" system is called "Meiyu front" in Taiwan. In previous studies, when the Meiyu front passed, it had the opportunity to converge with the prevailing wind field in front of the terrain in the northwestern part of Taiwan, resulting in a fast-moving airflow and the intensity of the jet, which is usually concentrated in the lower layers. It is therefore called a low-level jet. Low-level jets under certain conditions, known as barrier jets, can cause severe rainfall in northern Taiwan when they occur. The results of this study show that in the early morning of June 2, 2017, the Meiyu front approached northern Taiwan. When the main body of the front moved toward the Snow Mountain Range in northern Taiwan, a barrier jet appeared at an altitude of about 1 km. After the emergence of the barrier jets, sever precipitation occurred in Keelung and the northern coast of Taiwan in just 12 hours. Our research found that the emergence of barrier jets resulted in the increase of temperature gradients and vertical velocities in local areas; horizontal vortex tubes were twisted in the vicinity, and the horizontal wind shear on both sides of the jets enhanced the cyclonic circulation above the jets. And through the non-adiabatic effect, the stability of the release part was caused, resulting in a severe precipitation event in northern Taiwan. In this study, the observation data and model simulation results are compared with each other to analyze the main cause and physical mechanism of the severe precipitation in the northwest region in this case, and then to infer the dynamic and thermal processes of such weather phenomena over time.

How to cite: Hou, J. P., Su, L. Z., and Liao, Y. H.: A Case Study of Severe Precipitation Caused by Meiyu Front in Northwest Taiwan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2500, https://doi.org/10.5194/egusphere-egu2020-2500, 2020

D1958 |
Zhiqi Yang and Gabriele Villarini

Heavy precipitation has increased across many areas of the world, not only in terms of amounts but also of intensity and frequency, causing billions of dollars in economic losses and numerous fatalities. Our ability to prepare for and adapt to these events is tied to our understanding of the physical processes responsible for these events, and how they may respond to changes in anthropogenic forcings. Here we focus on the temporal clustering of heavy precipitation across Europe, highlight what the major climate drivers responsible for it are, and how it may change in response to changes in the concentration of greenhouse gasses. More specifically, we use a peak over threshold approach to identify heavy precipitation events, and Cox regression to relate the occurrence of these events to four climate modes that have been connected with the occurrence of heavy precipitation across Europe: the Arctic Oscillation (AO), the North Atlantic Oscillation (NAO), the East Atlantic (EA) pattern, and the Scandinavia pattern (SCAND). We use outputs from the Coupled Model Intercomparison Project Phase 5 (CMIP5), and experiments that allow us to focus on the response to CO2 (pre-industrial, 1pctCO2, abrupt4×CO2). To further detect the effects of downscaling on model-simulated precipitation, we also considered the accuracy of the EURO-CORDEX regional climate model (RCM) on capturing the temporal clustering in heavy precipitation across Europe. We find that: 1) the CMIP5 models can capture the temporal clustering in heavy precipitation across Europe as a function of these four climate modes; 2) the increases in CO2 are expected to lead to a strengthening of the relationship between the climate modes and the occurrence of heavy precipitation events; 3) the response to an abrupt increase in CO2 is generally stronger compared to a more gradual one.

How to cite: Yang, Z. and Villarini, G.: On the role of CO2 in enhancing the temporal clustering of heavy precipitation across Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2764, https://doi.org/10.5194/egusphere-egu2020-2764, 2020

Chat time: Monday, 4 May 2020, 10:45–12:30

Chairperson: A. Loukas, M.C. Llasat, U. Ulbrich
D1959 |
Tien-Hsiang Hsieh and Wen-Cheng Liu

  In Taiwan, when the rainy season comes, the extreme rainfall and typhoon events cause floods and economic losses in the middle and lower reaches, which impacts on the safety of people's lives. In this study, we took Dianbao River in Kaohsiung City as an example and simulated the rainfall-runoff in the upstream water catchment area based on the HEC-HMS model and used its results as the flow input condition of the FLO-2D model. The two models were validated by the Kongrey typhoon event in 2013 and the Megi typhoon event in 2016. In terms of upstream watershed, the analysis results of the HEC-HMS rainfall-runoff errors for the Kongrey typhoon and the Megi typhoon were as follows: percent errors of peak discharge (EQP) were 0.6% and 4.6%, respectively; errors of time to peak (ETP) were 0 hour and 2 hours, respectively; coefficients of efficiency (CE) were 0.89 and 0.91, respectively. In the Dianbao River, the FLO-2D model error analysis results of Kongrey typhoon and Megi typhoon events were as follows: percent errors of peak water level (EWP) were 13.51% and 4.71%, respectively; errors of time to peak (ETP) were 1 hour and 0 hour, respectively; coefficients of efficiency (CE) were 0.69 and 0.79, respectively. The simulation and validation of the two typhoon-inundated areas were reasonable and then the model was applied to explore the flood potential of the Dianbao River during different flood return periods.

KeywordsHEC-HMSFLO-2Drainfall-runofferror analysisflooding potential

How to cite: Hsieh, T.-H. and Liu, W.-C.: Analysis of flooding potential with different return periods-A case study of Dianbao River in Kaohsiung City, Taiwan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2806, https://doi.org/10.5194/egusphere-egu2020-2806, 2020

D1960 |
Ying Lung Liu, Chi-Yung Tam, and Sai Ming Lee

In this study, general circulation model (GCM) products were dynamically downscaled using the Regional Climate Model system version 4 (RegCM4), in order to study changes in the hydrological cycle - including extreme events - due to a warmer climate by the end of the 21st century over Southern China. The performance of 22 GCMs participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) in simulating the climate over the East Asian- western north Pacific region was first evaluated. It was found that MPI-ESM-MR, CNRM-CM5, ACCESS1-3, and GFDL- CM3 can reasonably reproduce the seasonal mean atmospheric circulation in that region, as well as its interannual variability. Outputs from these GCMs were subsequently downscaled, using the RegCM4, to a horizontal resolution of 25 km × 25km, for the period of 1979 to 2003, and also from 2050 to 2099, with the latter based on GCM projection according to the RCP8.5 scenario. Results show that the whole domain would undergo warming at the lower troposphere by 3 – 4 °C over inland China and ~2 °C over the ocean and low-latitude locations. Compared to the 1979-2003 era, during 2050-2099 boreal summer, the mean precipitation is projected to increase by 1 – 2 mm/day over coastal Southern China. There is also significantly enhanced interannual variability for the same season. In boreal spring, a similar increase in both the seasonal mean and also its year-to-year variations is also found, over more inland locations at about 25°N. Extreme daily precipitation is projected to become more intense, based on analyses of the 95th percentile for these seasons. On the other hand, it will be significantly drier during autumn over a broad area in Southern China: the mean rainfall is projected to decrease by ~1 mm/day. In addition, changes in the annual number of consecutive dry days (CDD) throughout the whole calendar year was also examined. It was found that CDD over the more inland locations will increase by ~5 days. Thus, there will be a lengthening of the dry season in the region. Global warming’s potential impact on sub-daily rainfall is also examined. For the rainfall diurnal cycle (DC), there is no significant change in both spatial and temporal patterns. Moisture budget analyses are also carried out, in order to ascertain the importance of change in background moisture, versus that in wind circulation, on the intensification of MAM and JJA mean rainfall as well as their interannual variability. The implication of these results on water management and climate change adaptation over the Southern China region will be discussed.

How to cite: Liu, Y. L., Tam, C.-Y., and Lee, S. M.: Investigating future changes in Southern China precipitation characteristics based on dynamically downscaled CMIP5 climate projections, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2987, https://doi.org/10.5194/egusphere-egu2020-2987, 2020

D1961 |
Maria-Carmen Llasat, Tomeu Rigo, Montserrat Llasat-Botija, Maria Cortès, Joan Gilabert, Anna del Moral, Isabel Caballero, Esther Oliver, and José A. Jiménez

The Mediterranean region is a hot spot for climate and environmental changes (Cramer et al., 2018). Climate change rates currently observed and expected in future scenarios in this region, exceed the global trends for most variables. Particularly, the average annual mean temperature has risen by 1.4°C since the pre-industrial times and it is expected that it could increase more than 1°C before the end of the century. The Mediterranean coastal zone comprises 75 coastal watersheds and 224 coastal administrative regions, with a total of 46,000 km of coastline.  This coastal zone concentrates about the 50 % of the population of the Mediterranean region while also attracts millions of tourists, supports a large network of infrastructures and, also, supports a large set of coastal and marine ecosystems delivering valuable services.

Regional climatic and geographical characteristics determine the area to be frequently affected by multiple hydrometeorological hazards such as thunderstorms, floods, windstorms and marine storms. These hazards together with the existence of high values at exposure determine the Mediterranean coastal fringe to be highly vulnerable and subjected to a high risk to the impact of extreme events, which will likely be worsened due to climate change (IPCC, 2018). Due to this, long-term planning of these coastal areas requires a proper assessment of their vulnerability and risk. Usually, this has been done by considering these hazards in an independent manner, although it is clear that a more holistic and integrated approach considering their  interdependencies and feedbacks is needed.

Within this context, this work  proposes an integrated risk index to classify the Mediterranean coastal municipalities in terms of their susceptibility to be affected by multiple hydrometeorological hazards, which will be later integrated with a similar index for marine  hazards. The index will be tested for a representative Mediterranean coastal area highly affected by hydrometeorological and marine hazards, the Catalonia and Valencia coastal zone (NE Spanish Mediterranean). The indicators represent different system characteristics determining the expected risk: a) climatic, b) geomorphological and  c) impact and perception components. The selected climatic indicators used have been: return period of precipitation, number of lightning strikes and maximum wind speed. Geomorphological indicators include average slope of the catchment area and surface within the municipality. Socioeconomic indicators have been estimated from the economical compensations paid by the Consorcio de Compensación de Seguros (the National insurance company), number of flood events that have affected each municipality estimated from their impact, and population awareness and social impact measured through analysing response in social media (tweets) to the impact of these hazards. Finally, as a matter of validation, the impact of the last flood events affecting this region is compared with the spatial distribution of the developed index.

This work has been developed in the framework of the M-CostAdapt project (FEDER/MCIU-AEI/CTM2017-83655-C2-2-R) where  the adaptability to Climate Change and natural risks of the Mediterranean coast is analysed by jointly considering natural maritime and terrestrial (hydrometeorological) hazards.

How to cite: Llasat, M.-C., Rigo, T., Llasat-Botija, M., Cortès, M., Gilabert, J., del Moral, A., Caballero, I., Oliver, E., and Jiménez, J. A.: Towards an integrated index on hydrometeorological risk in coastal Mediterranean Regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5147, https://doi.org/10.5194/egusphere-egu2020-5147, 2020

D1962 |
Chao Wang

Using ERA-Interim daily reanalysis and precipitation data, the combined effects of East Asia-Pacific (EAP) and Silk Road (SR) teleconnection patterns on summer precipitation in southern China were investigated on synoptic to sub-monthly timescales. Combined EAP and SR patterns lead to more persistent and extreme precipitation in the Yangtze River Valley (YRV) and exhibit an obvious zonal advance between the South Asia High (SAH) and Western Pacific Subtropical High (WPSH) prior to its onset. During typical combined events, an overlap between the SAH and WPSH remains in a favorable position for Persistent Extreme Precipitation (PEP). Furthermore, SR-induced acceleration of the westerly jet stream and extra positive vorticity advection provide persistent upper-level divergence for YRV precipitation. An anomalous EAP-related cyclone/anticyclone pair over East Asia induces enhanced low-level southwesterlies to the northern anticyclone flank and northerlies from the mid-latitudes, advecting anomalously abundant moisture toward the YRV, resulting in clear moisture convergence. Moreover, the strong ascent of warmer/moister air along a quasi-stationary front may be crucial for PEP. During decay, the SAH and WPSH diverge from each other and retreat to their normal positions, and the strong ascent of warmer/moister air rapidly weakens to dissipation, terminating PEP in the YRV.

How to cite: Wang, C.: Combined Effects of Synoptic-Scale Teleconnection Patterns on Summer Precipitation in Southern China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12374, https://doi.org/10.5194/egusphere-egu2020-12374, 2020

D1963 |
Tsuyoshi Hoshino and Tomohito Yamada

Typhoon Hagibis (2019) caused heavy rainfall and big flood damage in many river basins in Japan. In this research, we suggested the risk assessment method for heavy rainfall due to typhoon from the view point of a typhoon track by using records of rain gauges and typhoon track data from 1951. The relationships between typhoon position and rainfall intensity were obtained from the rain gauges and the typhoon track data for each rain gauge points. The relationships make it clear that typhoon track passes through the areas in which heavy rainfall occurred. The relationship can be used for risk assessment of heavy rainfall  in terms of typhoon track. The track of Typhoon Hagibis is the heaviest rainfall track for some points located in north of the typhoon track. However, some points close to the typhoon center or in south of the typhoon track are not the heaviest rainfall track. It means that if typhoon Hagibis shifted the track, the typhoon would cause heavier rainfall in some points. The result can be used not only for estimation of potential rainfall but also for selection of dangerous typhoons from large ensemble dataset. We assessed heavy rainfall risk of typhoons similar to typhoon Hagibis under historical and future climate by using the large ensemble climate dataset (d4PDF).

How to cite: Hoshino, T. and Yamada, T.: Assessment of heavy rainfall risk of typhoon Hagibis (2019) associated with typhoon track, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13748, https://doi.org/10.5194/egusphere-egu2020-13748, 2020

D1964 |
Antonio Francipane, Gianluca Sottile, Giada Adelfio, and Leonardo V. Noto

The increasing occurrence of flood events in some areas of the Southern Mediterranean area (e.g., Sicily), over the last few years, has contributed to raising the importance of characterizing such events and identifying their causes. Since most of these events can be related to high-intensity rainfalls, which, in turn, are usually due to convective rainfall, it is very important to understand which factors could be recognized as drivers of such extreme events. Nevertheless, the way to distinguish between convective and stratiform rainfall is still an open issue and not easy to solve.
With this regard, starting from precipitation time series recorded at different rain gauge stations of Sicily, which is the greatest Mediterranean island, we propose an algorithm capable to classify precipitation distinguishing between their convective and stratiform components.
In order to do that, a dataset from the regional agency SIAS (Servizio Informativo Agrometeorologico Siciliano - Agro-meteorological Information Service of Sicily) has been used because of its high temporal resolution, quality, and availability of up-to-date data. Specifically, data from rain gauge stations spread over the entire island have been collected for the period 2003 - 2018 and with a temporal resolution of 10 minutes.
In order to classify the precipitation in convective and stratiform components, the functional PCA-based clustering approach (denoted by FPCAC) has been applied, which can be considered as a variant of a k-means algorithm based on the principal component rotation of data. In order to evaluate the validity of the proposed algorithm, finally, the results have been compared to some ERA5 reanalysis products.

How to cite: Francipane, A., Sottile, G., Adelfio, G., and Noto, L. V.: Convective and stratiform precipitation: A PCA-based clustering algorithm for their identification, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18518, https://doi.org/10.5194/egusphere-egu2020-18518, 2020

D1965 |
Damián Insua-Costa, Gonzalo Miguez-Macho, Marc Lemus-Canovas, and María Carmen Llasat

The western Mediterranean region (WMR) often suffers from the devastating effects of flooding, caused by enormous rain accumulations that sometimes resemble the values produced by tropical systems. The ensuing socio-economic impact is so high that some of these extreme precipitation events are remembered and studied for decades. The main underlying reason for the high frequency of flooding in the WMR is that its precipitation regime presents a strong seasonality, with a maximum in late autumn associated with the development of strong convective situations that give rise to relatively short but intense periods of rain.

Here, we use the MESCAN precipitation analysis to detect daily heavy precipitation events in the WMR for the period 1980-2015. We consider a particular day as extreme if the precipitation for that day exceeds a threshold, which is based on normalized daily precipitation anomalies combined with a constant value.  The selected events are ranked according to their magnitude, defined on the basis of the amount and intensity of rain as well as the total extent affected. We then associate a weather pattern to each detected event. The methodology used to classify extreme days by weather types is based on a principal component analysis (PCA) approach. Specifically, we apply a PCA to a temporal mode matrix of 500 hPa geopotential height and mean sea level pressure, both obtained from ERA-5 reanalysis data. Our results show that the atmospheric configurations leading to torrential rainfall in the WMR are very reduced and recurrent; only four weather types are present in most of the extreme days. One of the main novelties of this study is that we can distinguish between more and less intense cases, so we were able to ascertain that only two of these four weather types are responsible for the majority of the most severe cases.

How to cite: Insua-Costa, D., Miguez-Macho, G., Lemus-Canovas, M., and Llasat, M. C.: Potentially catastrophic precipitation events and associated weather types in the western Mediterranean area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20156, https://doi.org/10.5194/egusphere-egu2020-20156, 2020

D1966 |
Martin Widmann, Michael Angus, Andrew Orr, and Gregor Leckebusch

It is estimated that around 10% of India’s population (or 130 million people) are acutely exposed to flooding resulting from intense rainfall, particularly during the main monsoon season (June to September). Such severe weather and accompanying flooding can result in considerable disruption to human communities and individuals by causing loss of life, damage to property, loss of livestock, destruction of crops and agricultural land, and deterioration of health conditions owing to waterborne diseases. To provide early warning of these heavy rainfall events, reliable impact-focused forecasting from operational weather forecasting centres such as NCMRWF (National Centre for Medium Range Weather Forecasting) and IMD (Indian Meteorological Department) is crucial.

Yet, despite the advances in numerical weather predictions and the state-of-the-art models used in India, accurately forecasting extreme weather at these scales is still difficult, and the intensity and spatial structure of predicted precipitation can both exhibit large errors. These errors are mainly caused by the limited resolution of weather forecasting models, and the resulting lack of adequate representation of small-scale processes. Some of them can be substantially reduced by statistical postprocessing of the forecasts taking into account past observations. However, currently no postprocessing methods for precipitation are applied to the weather forecasts over India.

Here, we present first results of postprocessing precipitation ensemble forecasts for India with local Quantile Mapping. Given our focus on heavy precipitation and the associated problem of a low number of cases and high sampling variability for the simulated and observed empirical Probability Density Functions (PDFs), we employ both standard, non-parametric PDFs but also parametric PDFs based on the Gamma and Generalised Extreme Value distributions.

This work is part of the ‘Weather and Climate Science for Service Partnership India’ (WCSSP-India) project ‘Heavy Precipitation forecast Postprocessing over India (HEPPI)’. Quantile Mapping is a member-by-member postprocessing method that essentially retains the spatial structure of the raw simulation. Within HEPPI we will also test ensemble-based methods and methods that adjust the spatial structure. This work provides the basis for further integration of meteorological and hydrological predictions.

How to cite: Widmann, M., Angus, M., Orr, A., and Leckebusch, G.: Postprocessing heavy precipitation forecasts for India with Quantile Mapping, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19476, https://doi.org/10.5194/egusphere-egu2020-19476, 2020

D1967 |
Aditya N. Mishra, Douglas Maraun, Heimo Truhetz, Emanuele Bevacqua, Raphael Knevels, Herwig Proske, Helene Petschko, Alexander Brenning, and Leopold Philip

During 22-24 June 2009, Austria witnessed a rampant rainfall spell that spread across populated areas of the country. High-intensity rainfall caused 3000+ landslides in Feldbach, and property damages worth €10,000,000 in Styria itself. Numerous synoptic-scale studies indicated the presence of a cut-off low over the Adriatic and excessive moisture convergence behind the extreme event. In a warmer climate change scenario, such an extreme precipitation event may become more intense due to higher water holding capacity of air with increased temperatures, but this reasoning may not be so straightforward considering the complex physics of precipitation.

Precipitation, as a natural atmospheric phenomenon, is dependent upon the dynamic and thermodynamic characteristics of the atmosphere. While it is safe to say that the thermodynamic characteristics of the atmosphere are relatively easier to simulate with confidence using available global models, the same cannot be said about the dynamics. This can be blamed on the chaotic non-linear behaviour of the atmosphere and problem in resolving sub-grid scale processes that reduce the model accuracy for longer spatial scales.

CCLM regional model is used to study this extreme precipitation event. Our setup uses IFS data to calculate initial and boundary conditions for the simulations of the ‘present’ case where our attempt is to recreate the event over the same location as the original event. Further we use CMIP5 global climate models (at the RCP8.5) scenario. In particular, these will be applied in the ‘surrogate climate change’ method. Here, the climate change signals are calculated by computing the difference between the thermodynamic fields of the CMIP5 simulations for the future and the past. These climate change signals are applied to the original fields to obtain the ‘changed’ fields which are used to calculate new initial and boundary conditions resembling a climate-change future. A similar approach is to be applied for the ‘past’ case simulations.

The idea behind this experimental setup is to establish a ‘storyline’ for the event as it would have occurred in the past, present and the future. The storyline approach provides an alternative to the traditional probabilistic approach for assessing risk enhancement and can serve to study responses of different mechanisms to climate change. The storyline approach also helps in decision-making as event-oriented risk management is easy for people to perceive and respond to. An associated landslide modelling study, which uses the precipitation output of our simulations as input, looks into the probable increased risks of landslides in the region and will directly aid the lives of those living in Southeast Austria.

How to cite: Mishra, A. N., Maraun, D., Truhetz, H., Bevacqua, E., Knevels, R., Proske, H., Petschko, H., Brenning, A., and Philip, L.: Climate Change’s Influence on June 2009 Extreme Precipitation Event Over Southeast Austria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14631, https://doi.org/10.5194/egusphere-egu2020-14631, 2020

D1968 |
Stefanie Gubler, Sophie Fukutome, and Christoph Frei

Extreme high temperatures have a strong impact on human well-being. In Switzerland, for instance, mortality has been shown to increase during strong heat waves (e.g., Ragettli et al., 2017) such as those that occurred in 2003, 2015, or 2018. Knowledge on the recurrence of such heat waves is therefore important, but conventional analysis of observational series is challenged by their rare occurrence (limited sampling), long-term trends, and strong seasonality (non-stationarity). This work presents a methodology, to derive reliable recurrence estimates of extreme maximum and minimum temperature events, taking account of gradual trends and seasonality in the data.

Temperature in Switzerland undergoes pronounced seasonal fluctuations, both in mean value and variance. In addition, a significant warming occurred over the last decades. To derive robust estimates on the rarity of a given extreme temperature event, it is important that these non-stationarities are formally modelled. Our modelling assumes that observed daily temperatures at stations are a superposition of a gradual, non-linear trend and residuals from a skewed T-distribution. The parameters of that distribution are assumed to vary over the year as second order harmonic functions. The model parameters are estimated using maximum likelihood. Thanks to this modelling, the existing daily temperature data can be transformed into a standard normal distribution, and the probability of an event can thus be assessed with respect to the climate at the time of measurement (year, calendar day).

With this methodology in hand, we analyze heat waves of the past, focusing on extreme temperatures at the beginning of summer when mortality risks are higher (Ragettli et al, 2017). We show how the risk of extreme heat has changed in the past, and how very rare events have become much more frequent in the present climate.


Ragettli, M., Vicedo-Cabrero, A. M., Schindler, C., and M. Röösli (2017): Exploring the association between heat and mortality in Switzerland between 1995 and 2013, Environmental Research, 158, 703-709, https://doi.org/10.1016/j.envres.2017.07.021.

How to cite: Gubler, S., Fukutome, S., and Frei, C.: Recurrence of extreme temperatures in Switzerland from 1965 to 2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10871, https://doi.org/10.5194/egusphere-egu2020-10871, 2020

D1969 |
Carlos Calvo-Sancho and Yago Martín

Supercells are the most organized and complex type of thunderstorms. Their formation, among other factors, is greatly influenced by general synoptic weather conditions. The goal of the study is to analyze the effect of different circulation weather types (CWT) in supercell formation and their spatiotemporal patterns in Spain. We use 2014-2018 data from the Spanish Supercell Database from the weather online network Tiempo.com (Martín et al., 2019) and compute 12 different CWTs through a Principal Component Analysis (PCA) of the 6-hour average of the 500hPa atmospheric pressure variable from the National Center for Environmental Prediction (NCEP) Reanalysis database. Results indicate that supercells are more common in three CWTs related with short-wave troughs over the Iberian Peninsula, particularly in the period from May to September. In these three CWTs the spatial distribution mainly concentrates in northeastern Spain, particularly in the Middle Ebro Valley (MEV) and the easternmost part of the Iberian System.

How to cite: Calvo-Sancho, C. and Martín, Y.: The influence of synoptic weather patterns in supercell formation in Spain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-40, https://doi.org/10.5194/egusphere-egu2020-40, 2019

D1970 |
Naveen Sudharsan, Jitendra Singh, Subimal Ghosh, and Subhankar Karmakar

In the recent past, India has experienced an increase in daily maximum and minimum temperature by 0.8 to 1 °C and 0.2 to 0.3 °C, respectively, along with an increased number of heatwave days. Human fatality, morbidity and discomfort are often reported due to the frequent heatwaves in India. To understand the effect of humidity in heatwaves over India, here in this study, we have classified the heatwaves into oppressive (high temperature and high humidity) and extreme (high temperature and low humidity) using excess heat factor approach. The rate of increase in oppressive heatwave days is exceeding that of the extreme heatwave days, even though the total number of oppressive heatwave days is fewer than the extreme heatwave days in the considered period (1953 to 2013). Moreover, the oppressive heatwave days are found to be the fatal one, as it is well correlated with the heat-related deaths in India.

As per COP 21 agreement, countries pledged to maintain the global temperature well below a 2 °C above the pre-industrial levels while attempting to limit the same to 1.5 °C. Taking these two warming scenarios, we have identified the heatwave events in near-future (2035 to 2065) and far-future (2070 to 2100). The number of oppressive heatwave days is expected to show an alarming five-fold increase at 2 °C warming (comparing to the period 1976 to 2005) by the end of the century. Limiting the warming to 1.5 °C from the proposed 2 °C results in a 67% reduction in oppressive heatwave days. A substantial jump in the number of oppressive heatwave days when compared with extreme heatwave days proposes that the Indian population is expected to be severely affected by heatwaves in the future amidst inadequate adaptive measures.

How to cite: Sudharsan, N., Singh, J., Ghosh, S., and Karmakar, S.: India can't Wait to Act upon Climate Change as Heatwaves Claim Life, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1071, https://doi.org/10.5194/egusphere-egu2020-1071, 2019

D1971 |
Hejing Wang and Dehai Luo

In our study, we aim to examine what factors lead to the summer heat waves over Eurasia and their variability. The analysis reveals that the summer heat waves over Eurasia show two kinds of spatial patterns: midlatitude and high latitude types. The mid-latitude heat wave mainly occurred over west Russia in the west of 55°E and in the south of 60°N, whereas the high-latitude type mainly occurred over west Russia in the east of 55°E and in the north of 55°N. We further analyzed the relationship of the two kinds of heat waves with atmospheric circulation patterns in the Atlantic-Eurasian sector and sea surface temperature (SST) anomalies over the North Atlantic and Arctic. The results show that the cold or warm SST anomalies over Barents-Kara Seas (BKS) can significantly influence the latitude and longitude of Russian heat waves, while the heat waves are also related to the latitude of positive SST anomalies over North Atlantic.

A mid-latitude wave train propagating into Eurasia and mid-latitude Russian heat waves, which are related to the positive phase of the North Atlantic Oscillation (NAO), are seen when there are strong SST warming in the North Atlantic mid-high latitudes south of 60°N and SST cooling over BKS. In contrast, a high-latitude Russian heat wave can occur over west Russia when there are positive SST anomalies over Baffin Bay, Davis Strait and Labrador Sea north of 60°N and BKS, while this high-latitude wave train is related to the decay of Greenland blocking or the negative NAO phase via high-latitude wave train propagation.

How to cite: Wang, H. and Luo, D.: Summer Eurasian Heat Wave and its linkage to SST anomalies over North Atlantic and Barents-Kara Seas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1218, https://doi.org/10.5194/egusphere-egu2020-1218, 2019

D1972 |
Francisco Javier Acero, Javier Portero, and José Agustín García

Heat waves are meteorological events exceptionally extremes that are increasing in frequency, duration and intensity. The Iberian Peninsula is characterized in the last decades by an increase in the trend of extreme temperature events and its consequences are important not only for the effects over the population but also for agriculture and biodiversity. The main objective in this study is to analyse future trends over the 21st century for extreme temperature using two events: heat waves and warm events. These are defined as the period of at least two consecutive days with temperatures over a certain threshold, the 95th percentile for heat waves and the 75th percentile for warm events. For this purpose, 14 different regionalized dynamic climate projections dataset are used. Firstly, to choose the better climate models, the common period 1961-2000 is used to compare with observational data obtained from SPAIN02 grid dataset. Once the better climate models are selected, trends in both events are analysed for the past (1961-2000) and the future (2011-2099). To estimate trends, Mann-Kendall test and Theil-Sen estimator were applied. Mann-Kendall test returns the significance of the trends for each grid point, while Theil-Sen estimator estimates the value of that trend. Moreover, max-stables processes are used to compare spatial dependence between dynamic projections. The results for the comparison period show that maximum temperature and moderate values of the maximum temperature are increasing smoothly, while low values of maximum temperatures are increasing even faster. This means that the variability of extreme temperature is decreasing, especially in the Mediterranean area of the Iberian Peninsula. For the 21st century, results reveal a significant positive trend in low values of the maximum temperatures that increases throughout the century over the whole study area. Warm events show a significant positive trend in frequency and intensity. This trend drastically increases from 2050 onwards.

How to cite: Acero, F. J., Portero, J., and García, J. A.: Trends of extreme temperature events over the Iberian Peninsula during the 21st century, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3327, https://doi.org/10.5194/egusphere-egu2020-3327, 2020

D1973 |
Cunmin Guo and Weihua Fang

Strong winds over the sea surface induced by tropical cyclones (TCs) of Northwest Pacific (NWP) basin have been posing great threats to maritime activities, and quantitative assessment on its hazard intensity is of great importance. In the past, most studies focused on the modeling of winds over the land and areas of major island areas numerically or statistically. However, there is no systematic assessment of TC wind hazard over the NWP basin with long-term wind time series based on windfield modeling of historical TC events. In this study, the footprints of historical TC events during 1949~2019 were modeled based on the parametric models developed in previous studies, which simulate the winds of both gradient layer and planetary boundary layer. The historical TC track data were obtained from the China Meteorological Administration, and the wind records from the Global Telecommunication System (GTS) data were used for the calibration and validation of the models. The spatial resolution of the modeling output is 1km for winds over the sea surface. In order to reflect wind speed heterogeneity over the land of small islands, the wind speeds were modeled with 90-meter resolution by considering local terrain effects and roughness heights of islands, derived from 90m SRTM DEM data and 30m land-used data. Based on the simulated wind footprints of the 2384 TC events during 1949~2019, the relationships between wind intensity and frequency of each modeling pixel were analyzed and fitted with General Extreme Value (GEV) distribution. A series of wind hazard maps, including wind speeds for return periods of 5a, 10a, 20a, 50a and 100a, and the exceedance probabilities of wind scales from 10 to 17, etc were produced. These wind hazard maps are useful to the management of TC disaster risks in the NWP basin.

How to cite: Guo, C. and Fang, W.: Assessment on the wind hazard of tropical cyclones over the Northwest Pacific basin with parametric wind field model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4124, https://doi.org/10.5194/egusphere-egu2020-4124, 2020

D1974 |
Jina Park, Hyungjun Kim, Shih-Yu(Simon) Wang, Jee-Hoon Jung, Kyo-Sun Lim, and Jin-Ho Yoon

In 2018, Japan experienced successive extremes, flood and following heat wave. The East Asian summer monsoon (EASM) has lifecycle and depending on the cycle, the basic condition of rainfall and heat event is decided. Thus, to examine the variability to the basic condition which is capable to make extreme event favorable, the long-term change of the EASM lifecycle is analyzed based on observation datasets and historical simulations of the Couple Model Intercomparison Project Phase 6 (CMIP6).

 According to the observation, the active phase of EASM has intensified and the break phase becomes longer, resulting in a shorter but stronger rainy season followed by a longer dry spell. This intensification in the precipitation evolution is accompanied by increased lower tropospheric southwesterly wind and convergence of water vapor flux, suggesting a dynamical cause. The widely reported westward extension of the Western North Pacific Subtropical High associated with the warming climate is a likely driver. Some of the CMIP6 models were able to capture the climatology of the EASM lifecycle and its intensification similar to those observed, but the majority of models still did not properly simulate the EASM lifecycle.

How to cite: Park, J., Kim, H., Wang, S.-Y., Jung, J.-H., Lim, K.-S., and Yoon, J.-H.: Long-term intensification of the East Asian Summer Monsoon (EASM) lifecycle based on observation and CMIP6, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4359, https://doi.org/10.5194/egusphere-egu2020-4359, 2020

D1975 |
Xiaoli Yang

Global climate change not only affects the processes within the water cycle but also leads to the frequent occurrences of local and regional extreme drought events. In China, spatial and temporal characterizations of drought events and their future changing trends are of great importance in water resources planning and management. In this study, we employed self-calibrating Palmer drought severity index (SC-PDSI), cluster algorithm, and severity-area-duration (SAD) methods to identify drought events and analyze the spatial and temporal distributions of various drought characteristics in China using observed data and CMIP5 model outputs. Results showed that during the historical period (1961–2000), the drought event of September 1965 was the most severe, affecting 47.07% of the entire land area of China, and shorter duration drought centers (lasting less than 6 months) were distributed all over the country. In the future (2021–2060), under both RCP[CF1]  4.5 and RCP 8.5 scenarios, drought is projected to occur less frequently, but the duration of the most severe drought event is expected to be longer than that in the historical period. Furthermore, drought centers with shorter duration are expected to occur throughout China, but the long-duration drought centers (lasting more than 24 months) are expected to mostly occur in the west of the arid region and in the northeast of the semi-arid region.

How to cite: Yang, X.: Spatial and Temporal Characterization of Drought Events in China Using the Severity-Area-Duration Method , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6429, https://doi.org/10.5194/egusphere-egu2020-6429, 2020

D1976 |
Jianying Feng, Yu Zhang, and Suping Wang

In 2018, severe meteorological drought occurred in the southwest of Northeast China, the  east-central of Inner Mongolia and the east of North China. Drought shows obvious regional and stage nature .In early March, mild to moderate drought appeared in North China, followed by severe drought in parts of northern and eastern of Hebe province. After the middle of April, the drought was alleviated obviously, and the drought in the southwest of Northeast China began to show signs. In  early May, there was mild to moderate drought in the central and eastern part of Inner Mongolia, and the drought in Northeast China developed. From June to early August, severe drought and above occurred in parts of Liaoning province , Inner Mongolia and North China. In mid-August, in addition to Liaoning province and North China, there were scattered light to moderate drought, drought relief in the northern China. In early September, the drought in North China increased and the range spread northward, and there were droughts of different degrees in the whole North China.In winter, there is only mild drought in North China.

The drought in this region has affected the agricultural production in different degrees. Spring sowing is blocked in the east of Inner Mongolia and the west of Northeast China, and high temperature in summer leads to the development of drought, corn and rice and other crops are adversely affected.

From spring to autumn, the precipitation in most parts of the drought disaster  area is less than 10-40%, and the temperature is higher than 1-2 ℃. The lack of precipitation and abnormal high temperature accelerated the loss of surface water, which resulted in the occurrence of drought in this area.

In spring of 2018, the middle and high latitudes are generally controlled by flat air flow, which is not conducive to the establishment of trough ridge, making the northern dry area lack of favorable precipitation conditions; in summer and autumn, the existence of Baikal Lake high-pressure ridge, resulting in circulation patterns that are not conducive to the precipitation conditions in the northern dry area. Among them, the obvious flat air flow in spring and the obvious high pressure ridge in summer are the main reasons for the outstanding drought in spring and summer in the northern arid area.

How to cite: Feng, J., Zhang, Y., and Wang, S.: Drought Events and Causes in North China in 2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7305, https://doi.org/10.5194/egusphere-egu2020-7305, 2020

D1977 |
Uwe Ulbrich and Jens Grieger

The ClimXtreme program funded by the German Ministry of Education and Research is designed to address Physics and Processes, Statistics, and Impacts of meteorological extreme events, considering both the past period covered by instrumental measurements, and future climate scenarios. In its branch on impacts, the impact of hazards in Europe (convective events, severe precipitation, heat waves and droughts, and large scale storms) shall be considered in order to identify the underlying relevant weather situations and the antecedent meteorological factors. The specific characteristics of the extreme events shall also be explored. Aiming at a better understanding of the impacts of the extremes, investigations shall go beyond quantification of the local severity of a hazard. The assumption is that there is also an influence of weather and climate on exposure and vulnerability. These factors for the occurrence and the magnitude of damaging impacts  thus depend on local climatology, the occurrence of specific weather sequences augmenting vulnerability, or the occurrence of specific combinations of factors which individually needn’t be extreme (compound events).  One starting point are thus already existing impact models, which do not take (all of) these factors into account. Results from numerical climate models will be used to estimate the future change of risks under climate change.

How to cite: Ulbrich, U. and Grieger, J.: An approach towards addressing meteorological factors for extreme event impacts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11050, https://doi.org/10.5194/egusphere-egu2020-11050, 2020

D1978 |
Qin Su

The changes in three aspects of frequency, intensity and duration of the compound, daytime and nighttime heat waves (HWs) over China during extended summer (May–September) in a future period of the mid-21st century (FP; 2045-2055) under RCP4.5 scenario relative to present day (PD; 1994-2011) are investigated by two models, MetUM-GOML1 and MetUM-GOML2, which comprise the atmospheric components of two state-of-the-art climate models coupled to a multi-level mixed-layer ocean model. The results show that in the mid-21st century all three types of HWs in China will occur more frequently with strengthened intensity and elongated duration relative to the PD. The compound HWs will change most dramatically, with the frequency in the FP being 4–5 times that in the PD, and the intensity and duration doubling those in the PD. The changes in daytime and nighttime HWs are also remarkable, with the changes of nighttime HWs larger than those of daytime HWs. The future changes of the three types of HWs in China in two models are similar in terms of spatial patterns and area-averaged quantities, indicating these projected changes of HWs over the China under RCP4.5 scenario are robust. Further analyses suggest that projected future changes in HWs over China are determined mainly by the increase in seasonal mean surface air temperatures with change in temperature variability playing a minor role. The seasonal mean temperature increase is due to the increase in surface downward longwave radiation and surface shortwave radiation. The increase in downward longwave radiation results from the enhanced greenhouse effect and increased water vapour in the atmosphere. The increase in surface shortwave radiation is the result of the decreased aerosol emissions, via direct aerosol-radiation interaction and indirect aerosol-cloud interaction over southeastern and northeastern China, and the reduced cloud cover related to a decrease in relative humidity.

How to cite: Su, Q.: Projected near-term changes in three types of heat waves over China under RCP4.5, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12349, https://doi.org/10.5194/egusphere-egu2020-12349, 2020

D1979 |
Jieun Kim, Jaehyung Yu, Sang Kee Seo, Jin-Hee Baek, and Byung Chil Jeon

The climate change causes major problems in natural disasters such as storms and droughts and has significant impacts on agricultural activities. Especially, global warming changed crops cultivated causing changes in agricultural land-use, and droughts along with land-use change accompanied serious problems in irrigation management. Moreover, it is very problematic to detect drought impacted areas with field survey and it burdens irrigation management. In South Korea, drought in 2012 occurred in western area while 2015 drought occurred in eastern area. The drought cycle in Korea is irregular but the drought frequency has shown an increasing pattern. Remote sensing approaches has been used as a solution to detect drought areas in agricultural land-use and many approaches has been introduced for drought monitoring. This study introduces remote sensing approaches to detect agricultural drought by calculation of local threshold associated with agricultural land-use. We used Landsat-8 satellite images for drought and non-drought years, and Vegetation Health Index(VHI) was calculated using red, near-infrared, and thermal-infrared bands. The comparative analysis of VHI values for the same agricultural land-use between drought year and non-drought year derived the threshold values for each type of land-use. The results showed very effective detection of drought impacted areas showing distinctive differences in VHI value distributions between drought and non-drought years.

How to cite: Kim, J., Yu, J., Seo, S. K., Baek, J.-H., and Jeon, B. C.: Determination of Drought Threshold for Agricultural Land-use using Satellite Image Analysis Techniques, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12421, https://doi.org/10.5194/egusphere-egu2020-12421, 2020

D1980 |
Damjan Jelic, Petra Mikus Jurkovic, Barbara Malecic, Barbara Vodaric Surija, Maja Telisman Prtenjak, and Natasa Strelec Mahovic

In western and central regions of Croatia, as well as Istria peninsula, hail activity is monitored by hail pads and hail observations, the analyses of which shows that these regions have a significant frequency of high-intensity hail events. On 25 June 2017 weather conditions were favorable for development of several MSC in the region, some of which organized into a squall lines, causing severe weather effects over larger portion of Croatia. Hail pad networks reported 46 records of hail all over the region introducing one of the largest number of records in one day. Hail size varied between 1 and 2 cm with exception of 2 stations recording 2.5 and 3.1 cm diameters. Since the episode covers large area and offers high number of hail pad data it is suited for testing other indirect methods for assessment of hail. We are investigating capabilities of satellite products based on HRV and colored enhanced IR 10.8 µm channels (overshooting tops, plume, cold ring...), lightning activity and lightning jump activity to estimate hail occurrence and for the first time for Croatia, inspect radar products in assessing hail intensity.

How to cite: Jelic, D., Mikus Jurkovic, P., Malecic, B., Vodaric Surija, B., Telisman Prtenjak, M., and Strelec Mahovic, N.: Estimation of hail occurrence from satellite, lightning and radar data in Croatia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14751, https://doi.org/10.5194/egusphere-egu2020-14751, 2020

D1981 |
| Highlight
Gizaw Mengistu Tsidu

The Nile River Basin has been vital source of water to Riparian countries in both upper and lower catchments of the Basin. However, the states in the lower catchment namely Sudan and Egypt have exploited this resource without significant competition from countries in the upper catchments in the past. Recently, due to population increase in the basin and climate change, there are some initiatives by Riparian States such as Ethiopia to use this vital water resource (e.g., for energy generation). Therefore, it is important to understand recurrent drought characteristics and its potential impacts on the water resource in the basin. Drought events in the Nile Basin have been extracted using run theory based on the Standardized Precipitation Evapotranspiration Index (SPEI) accumulated on the time scale of 12 months using CRU rainfall and evapotranspiration data, which covers the period 1901–2018. The drought events are characterized by four variables: duration, severity. Intensity and Inter-arrival time. The mean duration and severity of drought during the last 118 years over the Basin are generally short and moderate over upper catchments. Conversely, the mean duration various from 4 to 8 months and up to 14 months over the middle and lower catchments of the Basin respectively while the mean drought severity increases from -2 at upper catchment to -7 at lower catchment. Gamma, Weibull, Gamma and Exponential functions are then selected to describe the marginal distribution of severity, duration, intensity and inter-arrival time, respectively. The Gumbel–Hougaard Copula was used to construct the joint distribution of duration, severity, intensity and/or inter-arrival time. The results indicate that the return period is dependent on the location within the basin, variable type and the combination of variables. For extreme droughts with severity index of -10 and duration of 14 months, return periods are longer than 40 years over south parts of the Basin and it barely exceeds 25 years over northern parts of the Basin. Generally, the short return period is mainly distributed in lower catchments of the Basin. This study on the identification of spatial distributions of drought return periods across the Basin is therefore important for drought mitigation and strategic planning on the water resource.

How to cite: Mengistu Tsidu, G.: Spatial analysis of return periods of hydrological drought of Nile River Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18896, https://doi.org/10.5194/egusphere-egu2020-18896, 2020

D1982 |
Christelle Castet

Severe convective storms (SCS) cause widespread damages over Europe each year and can be responsible for billions of euros in losses. In addition, the expected increase in their frequency and intensity over the century represents a primary concern for insurers.

Parametric insurance, which compensates customers when an index reaches a predefined threshold, is a fast and transparent insurance solution, that requires a careful analysis of the risk and a correlation of the index with potential damages. For instance, to protect customers against wind related damages from SCS, an index based on wind speed could be used. Unfortunately, the modeling of precise surface wind fields associated with SCS remains a challenge and sources of observation are often patchy or not reliable. The goal is then to define a parameter that can be used to estimate the potential wind damage from SCS.

Relying on a 10-year climatology of lightning activity over Poland, our approach consists first in determining large scale environmental variables in the ERA5 reanalysis favorable to the occurrence of SCS. Then, a combination of variable is tested in correlation with wind related damages. Preliminary results suggest that lightning density is a good proxy to the intensity of convective cells, and to a lesser extent to wind related damages.

How to cite: Castet, C.: Severe convective storms and wind damage assessment over northwestern Poland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21142, https://doi.org/10.5194/egusphere-egu2020-21142, 2020

D1983 |
Onneile Nomsa Keitumetse and Gizaw Mengistu Tsidu

Recently there has been an increased water scarcity around the world due to high water demand, which is worsened by the recurrent drought characterized by long duration and high severity. However, these characteristics are important in drought monitoring and decision-making for reliable disaster early warning system, water resources planning and management. Semi-arid environments, of which Botswana is known for, exhibit high variability in climate leading to recurring droughts. Hence there is a need to conduct a study to understand the spatio-temporal variability of droughts over Botswana. The Standardized Precipitation Index (SPI) and the Standardized Evapotranspiration Index (SPEI) were used for analysing drought based on gridded rain gauge and evapotranspiration data referred to as Climatic Research Unit (CRU) covering a period of 1901-2018 at a time scale of 12 months. Both SPI and SPEI were able to detect the spatial and temporal variation of drought events. But SPEI was able to identify more droughts in the severe to moderate categories over a wider areas in the country than SPI does. The temporal trends of droughts mostly showed a significant drying trends. The conditional return period of drought of different categories was also determined in a multivariate context by coupling duration, severity, inter-arrival time of drought based on copula distribution and cumulative density functions. Drought events with high intensities had a low probability of occurrence while lower intensities had a high chance of occurrence within 5 to 10 years. Such information on the drought conditional probabilities can be useful in evaluating the water-supply capability and the needed supplementary water resources during severe droughts for a specific water-supply system. In particular, it is generally suitable for the long term planning and management of water resources systems over the country.

How to cite: Keitumetse, O. N. and Mengistu Tsidu, G.: Characterization of drought over Botswana: Towards a multivariate approach of drought prediction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22082, https://doi.org/10.5194/egusphere-egu2020-22082, 2020

D1984 |
Mei Mei
Based on surface observation meteorological data during 1961-2017 and ERA-interim reanalysis data, an evaluation method of different meteorological conditions for heavy air pollution (MCHAP) was set up by using atmospheric self-cleaning ability index (ASI). Through analyzing the historical variation characteristics of MCHAP of Beijing-Tianjin-Hebei region in autumn and winter, the results were as follows. During 1961-2017, the frequency and extremity of MCHAP in Jincheng of Shanxi province ranked the frst. MCHAP occurred more frequently in Beijing, Langfang of Hebei province and Zhengzhou of Henan province and more extremely in Baoding, Shijiazhuang and Hengshui of Hebei province. MCHAP had occurred in “2+26” cities around Beijing-Tianjin -Hebei region in history since 1961, but which were more common in recent years and caused much more sever air pollution events. During the period of 2013-2017, MCHAP occurred the least frequently in 2017 in “2+26” cities around Beijing-Tianjin-Hebei region except Beijing. However the extremity of MCHAP in 2017 receded a lot in Beijing. Both in the 1980s and the period of 2010-2017, MCHAP in the Beijing-Tianjin-Hebei and its surrounding areas took place the most frequently, which was affected by both the cold air intensity and the change of large-scale air stagnation condition. To some extent, the development of urbanization also plays a role in the decadal change of MCHAP.

How to cite: Mei, M.: Study on meteorological conditions for heavy air pollution and its climatic characteristics in “2+26” cities around Beijing-Tianjin-Hebei region in autumn and winter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22330, https://doi.org/10.5194/egusphere-egu2020-22330, 2020

D1985 |
Beijing Fang and Mengqian Lu

Severe heatwaves in recent decades caused tremendous financial loss and even deaths. And both the occurrence and characteristics of heatwave are changing under global warming. The spatiotemporal variation and characteristics of heatwave in Northeastern Asia are investigated on both grid and event bases in this study. We find that persistent, extensive and intense heatwave has become more frequent during the last four decades. Such trend is found significantly correlated with the increase of temperature.

As most dreadful heatwaves are reported to be accompanied by blocking, we also thoroughly analyze the association between heatwave and blocking using two leading blocking indices, examining 500hpa geopotential height (TM index) and vertically averaged potential vorticity anomaly (PV index), respectively. A discrepancy between blocking climatology of TM index and PV index is exhibited, with the former displaying two high-frequency zonal bands at the south and north regions, while the latter only showing one high frequency band in the north. However, grid-based concurrence analysis using the two blocking indices agreeably suggests that blocking favors the occurrence of heatwave, especially in the north region where blocking often occurs. We further explicitly investigate their extended temporal association with time lags, which has not been done before in the literatures. It reveals that heatwave mostly occurs after or on the onset day of blocking and ends after or at the end of blocking. It indicates that blocking is more of a favorable environmental condition to trigger heatwave than maintain it. Lastly, the impact of blocking on the characteristics of heatwave events is explored on an event basis, using the 3D object model newly proposed by this study. Blocking related heatwave events are more likely to be more persistent, extensive and intense than unrelated events.

How to cite: Fang, B. and Lu, M.: Investigating Spatiotemporal Variation of Heatwave and its Association with Blocking in the Northeastern Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2368, https://doi.org/10.5194/egusphere-egu2020-2368, 2020