NH1.4

Extreme meteorological and hydrological events induced by severe weather and climate change

With global climate change affecting the frequency and severity of extreme meteorological and hydrological events, it is particularly necessary to develop models and methodologies for a better understanding and forecasting of present-day weather induced hazards. Future changes in the event characteristics as well as changes in vulnerability and exposure are among the further factors for determining risks for infrastructure and society, and for the development of suitable adaptation measures. 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 (toxic) 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 (economic losses, infrastructural damages, human fatalities, pollution), 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 on damage prevention and damage reduction. In order to understand fundamental processes, papers are also encouraged that look at complex extreme events produced by combinations or sequences 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, environmental effects, hazard management and applications like insurance issues.

Co-organized by AS4/HS13
Convener: Athanasios Loukas | Co-conveners: Maria-Carmen Llasat, Uwe Ulbrich, Catrina Brüll, Piero BellanovaECSECS
Presentations
| Thu, 26 May, 08:30–11:50 (CEST), 13:20–14:50 (CEST)
 
Room C

Session assets

Session materials

Presentations: Thu, 26 May | Room C

Chairpersons: Athanasios Loukas, Maria-Carmen Llasat, Uwe Ulbrich
08:30–08:35
Extreme weather events
08:35–08:41
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EGU22-12077
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On-site presentation
Margarida L. R. Liberato and Alexandre M. Ramos

Despite being major sources of hazards and having impacts on local and national populations, environment and economies, processes involved in extremes’ intensification and generation of disastrous impacts, such as extreme and widespread dry and wet events or flash flooding, are not fully understood yet. Therefore, the goal of WEx-Atlantic project is to perform research, to improve knowledge on weather extremes in the North Atlantic European sector and to communicate it to society. Considered extremes are strong winds and heavy hydrometeorological (HM – dry and wet) events associated with extratropical cyclones (EC), frontal systems and atmospheric rivers (AR).

WEx-Atlantic contributes to improve our understanding on the assessment of weather systems and the underlying physical mechanisms, variability and expected changes under global warming, as well as meteorological, environmental (e.g. forest) and socioeconomic (e.g. renewable wind energy and power grid) impacts on Portugal including the Macaronesia Islands.

WEx-Atlantic applies state-of-the-art techniques to detect and track weather systems, including AR, mid-latitude systems and weather types to reanalysis datasets as well as to GCMs. Here a review of WEx-Atlantic research and new contribution is presented.

 

This work was supported by project “Weather Extremes in the Euro Atlantic Region: Assessment and Impacts—WEx-Atlantic” (PTDC/CTA-MET/29233/2017) funded by Fundação para a Ciência e a Tecnologia, Portugal (FCT). Alexandre. M. Ramos was supported by the FCT Scientific Employment Stimulus 2017 (CEECIND/00027/2017).

 

Algarra I, et al. Significant increase of global anomalous moisture uptake feeding landfalling Atmospheric Rivers. Nat Commun 11, 5082 (2020). https://doi.org/10.1038/s41467-020-18876-w

Gonçalves A, et al. Wind Energy Assessment during High-Impact Winter Storms in Southwestern Europe. Atmosphere. 2021; 12(4):509. https://doi.org/10.3390/atmos12040509

Hénin R, et al. A ranking of concurrent precipitation and wind events for the Iberian Peninsula. Int J Climatol.; 41(2), 1421-1437 (2021) https://doi.org/10.1002/joc.6829

Hénin R, et al. Assigning precipitation to mid-latitudes fronts on sub-daily scales in the North Atlantic and European sector: Climatology and trends. Int J Climatol.; 39(1), 317–330, (2019) https://doi.org/10.1002/joc.5808

Liberato MLR, et al. Rankings of extreme and widespread dry and wet events in the Iberian Peninsula between 1901 and 2016. Earth Syst. Dynam., 12, 197–210 (2021) https://doi.org/10.5194/esd-12-197-2021

Nieto R, et al. Contribution of the main moisture sources to precipitation during extreme peak precipitation months, Adv. Water Res., 131, (2019), 103385 https://doi.org/10.1016/j.advwatres.2019.103385

Ramos AM, et al. Impacts of Atmospheric Rivers in Extreme Precipitation on the European Macaronesian Islands. Atmosphere 2018, 9, 325, (2018) https://doi.org/10.3390/atmos9080325

Reale M, et al. A Global Climatology of Explosive Cyclones using a Multi-Tracking Approach, Tellus A, 71:1, 1-19, (2019) https://doi.org/10.1080/16000870.2019.1611340

Ribeiro SL, et al. Development of a catalogue of damage in Portuguese forest associated with extreme extratropical cyclones. Science of The Total Environment, 151948, 2021 https://doi.org/10.1016/j.scitotenv.2021.151948

Sorí R, et al. Hydrometeorological droughts in the Miño–Limia–Sil hydrographic demarcation (northwestern Iberian Peninsula): the role of atmospheric drivers, Nat. Hazards Earth Syst. Sci., 20, 1805–1832, (2020) https://doi.org/10.5194/nhess-20-1805-2020

Stojanovic M, et al. Consecutive Extratropical Cyclones Daniel, Elsa and Fabien, and Their Impact on the Hydrological Cycle of Mainland Portugal. Water. (2021); 13(11):1476. https://doi.org/10.3390/w13111476

Vázquez M, et al. Atmospheric Moisture Sources Associated with Extreme Precipitation During the Peak Precipitation Month. Weather and Climate Extremes, 30, 100289 (2020) https://doi.org/10.1016/j.wace.2020.100289

How to cite: Liberato, M. L. R. and Ramos, A. M.: Weather Extremes in the Euro Atlantic Region: Assessment and Impacts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12077, https://doi.org/10.5194/egusphere-egu22-12077, 2022.

08:41–08:47
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EGU22-2532
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ECS
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On-site presentation
Laura Esbrí, Tomeu Rigo, M. Carmen Llasat, and Antonio Parodi

This contribution has the main goal of identifying, characterizing, tracking and nowcasting severe thunderstorms using the Density of the Vertical Integrated Liquid (DVIL). The DVIL can synthesize all the volumetric information of a column of the weather radar in a 2D plane. This is, it estimates the quantity of precipitable liquid water in the column but, besides, it reduces the dependency on the height of the column. This point becomes crucial to give an appropriate weight of potential danger to thunderstorms that occurred out of the typical convective season. . This is particularly useful to improve the decision-making and early warning in critical environments and infrastructures, like airports and air traffic management (ATM). The usage of DVIL has multiple advantages, for instance, reducing the computational time consumed on the analysis of large areas. Also, to obtain a good and simple description of the potentially dangerous thunderstorms, and to have an easily integrating into other systems for ATM decision making. The main disadvantage is a less precise characterization of the atmospheric objects than with the whole radar volumetric data. Nevertheless, the differences are scarce and do not produce any significant inconvenience in the procedure. The algorithm first identifies those areas exceeding a DVIL threshold, which is established for thunderstorms with a certain probability of producing severe weather. The characterization module turns out simpler than in other methodologies because of the data type (2D instead of 3D reflectivity fields), but it can be combined with other data types if needed. The tracking and nowcasting procedure obtain the past trajectory of the thunderstorm and then use it to weather forecast from 5 to the next 60 minutes, with 5 minutes steps. Different convective episodes that have affected the proximity of Italian and Spanish airports have been analysed to evaluate the following points: (1) the performance of the correct identification of potentially dangerous thunderstorms, (2) the capability of tracking the path and characterizing the life cycle of those storms, and (3) the ability of the nowcasting to correctly forecast the time and the most dangerous area.

This project has received funding from the SESAR Joint Undertaking under grant agreement No 892362, SINOPTICA-H2020 (Satellite-borne and IN-situ Observations to Predict the Initiation of Convection for Air traffic management) project.

How to cite: Esbrí, L., Rigo, T., Llasat, M. C., and Parodi, A.: Using Vertical Integrated Liquid Density from a Weather Radar Network to Nowcast Severe Events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2532, https://doi.org/10.5194/egusphere-egu22-2532, 2022.

08:47–08:53
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EGU22-11732
Piero Lionello, Roberto Ingrosso, M.Marcello Miglietta, and Gianfausto Salvadori

The dynamics of tornadoes include large vorticity in the lower troposphere and an intense updraft, whose combination may result in their formation. In this study we investigate the possibility of using a statistical relation for their description. In fact, the nonlinearity, complexity and fine scale of these processes presently prevents their simulation in the atmospheric circulation models currently used for weather forecasts and climate projections. Here we use a large dataset of tornadoes observed in the USA and Europe and the data of ERA5 (ECMWF ReAnalysis 5) to establish a statistical link between the occurrence of tornadoes and factors whose values can be extracted from atmospheric circulation models. The values of CAPE (convective available potential energy), WS (wind shear in the lower troposphere), SRH (storm relative helicity) and LCL (lifting condensation level) of the high resolution (about 30km) ERA5 data have been considered. The analysis shows all these variables are significantly linked to the formation of tornadoes with WS and CAPE being the most relevant ones. The analysis is an extension of a former study (Ingrosso et al., 2020, 10.3390/atmos11030301) based on a dataset of tornadoes events much larger than previously, on higher resolution atmospheric data, and more prognostic variables. The results provide a new expression for the probability of occurrence of tornadoes that can be used for forecasting their likelihood with potential applications to their predictions and future changes of their frequency.

How to cite: Lionello, P., Ingrosso, R., Miglietta, M. M., and Salvadori, G.: Factors leading to the formation of tornadoes: statistical links emerging from a large dataset, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11732, https://doi.org/10.5194/egusphere-egu22-11732, 2022.

08:53–08:59
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EGU22-12589
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Virtual presentation
Addisu Hunegnaw, Hüseyin Duman, Gunnar Elgered, Jan Dousa, and Norman Teferle

Over the last few decades, anthropogenic greenhouse gas emissions have increased the frequency of climatological anomalies such as temperature, precipitation, and evapotranspiration. It is noticed that the frequency and severity of the intense precipitation signify a greater susceptibility to flash flooding. Flash flooding continues to be a major threat to European cities, with devastating mortality and considerable damage to urban infrastructure. As a result, accurate forecasting of future extreme precipitation events is critical for natural hazard mitigation. A network of ground-based GNSS receivers enables the measurement of integrated water vapour along slant pathways providing three-dimensional water vapour distributions. This study aims to demonstrate how GNSS sensing of the troposphere can be used to monitor the rapid and extreme weather events that occurred in central Europe in June 2013 and resulted in flash floods and property damage. We recovered one-way slant wet delay (SWD) by adding GNSS post-fit phase residuals, representing the troposphere's higher-order inhomogeneity. Nonetheless, noise in the GNSS phase observable caused by site-specific multipath can significantly affect the SWD from individual satellites. To overcome the problem, we employ a suitable averaging strategy for stacking post-fit phase residuals obtained from the PPP processing strategy to generate site-specific multipath corrections maps (MPS). The spatial stacking is carried out in congruent cells with an optimal resolution in elevation and azimuth at the local horizon but with decreasing azimuth resolution as the elevation angle increases. This permits an approximately equal number of observations allocated to each cell. The spatio-temporal fluctuations in the SWD as measured by GNSS closely mirrored the moisture field associated with severe weather events in central Europe, i.e., a brief rise prior to the main rain events, followed by a rapid decline once the storms passed. Furthermore, we validated the one-way SWD between ground-based water-vapour radiometry (WVR) and GNSS-derived SWD for different elevation angles.

 

How to cite: Hunegnaw, A., Duman, H., Elgered, G., Dousa, J., and Teferle, N.: Analysis of GNSS sensed slant wet delay during the severe weather events in central Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12589, https://doi.org/10.5194/egusphere-egu22-12589, 2022.

08:59–09:05
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EGU22-12168
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ECS
Estimating tropical cyclone rainfall using the STORM dataset
(withdrawn)
Natalie Lord, Nadia Bloemendaal, Ivan Haigh, Niall Quinn, Pete Uhe, and Chris Sampson
09:05–09:11
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EGU22-1758
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Virtual presentation
Matthias Röthlisberger, Barbara Scherrer, Andries Jan de Vries, and Raphael Portmann

The synoptic dynamics leading to the longest wet spells in Europe are so far poorly investigated, despite these events’ potentially large societal impacts. In this study we examine the role of cyclones and PV cutoffs for unusually long wet spells in Europe, defined as the 20 longest uninterrupted periods with at least 5 mm daily accumulated precipitation at each ERA-Interim grid point in Europe (this set of spells is hereafter referred to as S20). The S20 occur predominantly in summer over the eastern continent, in winter over the North Atlantic, in winter or fall over the Atlantic, and in fall over the Mediterranean and European inland seas. Four case studies reveal archetypal synoptic storylines for long wet spells: (a) A seven-day wet spell near Moscow, Russia, is associated with a single slow-moving cutoff-cyclone couple; (b) a 15-day wet spell in Norway features a total of nine rapidly passing extratropical cyclones and illustrates serial cyclone clustering as a second storyline; (c) a 12-day wet spell in Tuscany, Italy, is associated with a single but very large cutoff-complex, which is replenished multiple times by a sequence of recurrent anticyclonic wave breaking events over the North Atlantic and western Europe; and (d) a 17-day wet spell in the Balkans features intermittent periods of diurnal convective precipitation in an environment of weak synoptic forcing and recurrent passages of upper-level troughs and PV cutoffs and thus also highlights the role of diurnal convection for long wet spells over land. A systematic analysis of cyclone and cutoff occurrences during the S20 reveals considerable spatial variability in their respective role for the S20. For instance, cyclones and cutoffs are present anywhere between 10% and 90%, and 20% and 70% of the S20 time steps, respectively, depending on the geographical region. However, overall both cyclones and cutoffs, appear in larger number and at a higher rate during the S20 compared to climatology. Furthermore, in the Mediterranean, the PV cutoffs and cyclones are significantly slower moving and/or longer-lived during the S20 compared to climatology. Our study thus documents for the first time the palette of synoptic storylines accompanying unusually long wet spells across Europe, which is a prerequisite for developing an understanding of how these events might change in a warming climate and for evaluating the ability of climate models to realistically simulate the synoptic processes relevant to these events.

How to cite: Röthlisberger, M., Scherrer, B., de Vries, A. J., and Portmann, R.: The role of cyclones and PV cutoffs for the occurrence of unusually long wet spells in Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1758, https://doi.org/10.5194/egusphere-egu22-1758, 2022.

09:11–09:17
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EGU22-9357
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ECS
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On-site presentation
Aikaterini Anesiadou, Sandy Chkeir, and Riccardo Biondi

Extreme weather events in Europe have increased in frequency and intensity in the last decades, especially in some areas like Alpes and Balkans, and is expected to increase even more in the upcoming years due to the climate change. Monitoring and forecasting the severe weather events locally developed and in a short time range is very challenging but also very important for aviation safety. Several studies have been made for studying the pre-convective environment, however there are still gaps in the knowledge of the dynamical processes of regional and short duration deep convective systems.

This study is implemented within the SESAR ALARM project and focuses on the analysis of the pre-convective and convective environment in support to the air traffic management and air traffic control. The work focuses in the detection, analysis and nowcasting of severe weather events in a selected hotspot: the area of Milano Malpensa airport in Italy. We have used the data from 28 weather stations, 8 GNSS stations, radar and lightning detectors, in the period 2010-2020 to train a nowcasting algorithm and to characterize the pre-convective environment.

Our first results for different locations in the area of interest, show on average that the root mean square error of the rainfall prediction lie in the range 0.1029-0.2838 mm and 0.2720-0.7815 m/s for the wind speed prediction. Our algorithm shows the best rain predictive performance in the next 10 minutes higher than 90%, and higher than 80% in the next 30 minutes. Moreover, the pre-convective environment analysis shows that all the cases with wind field divergence never show an increasing trend of GNSS Zenith Total Delay before the event.

How to cite: Anesiadou, A., Chkeir, S., and Biondi, R.: Characterization and nowcasting of severe weather events over Milano Malpensa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9357, https://doi.org/10.5194/egusphere-egu22-9357, 2022.

09:17–09:23
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EGU22-1314
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On-site presentation
Thorsten Simon, Georg J. Mayr, Deborah Morgenstern, Nikolaus Umlauf, and Achim Zeileis

Motivation: The response of lightning to a changing climate is not fully understood. Historic trends of proxies known for fostering convective environments suggest an increase of lightning over large parts of Europe. Since lightning results from the interaction of processes on many scales, as many of these processes as possible must be considered for a comprehensive answer.

Objectives: Our aim is a probabilistic reconstruction of summer lightning over the European Eastern Alps down to its seasonally varying diurnal cycle. This necessitates consideration of many processes which becomes feasible by combining a statistical learning approach with several recent scientific achievements: Decade-long seamless lightning measurements by the Austrian Lightning Detection & Information System (ALDIS) and hourly reanalyses of atmospheric conditions including cloud micro-physics within the fifth generation ECMWF atmospheric reanalysis (ERA5).

Methods: These two data sets have been linked by the statistical learning approach called generalized additive model (GAM). GAMs are capable to identify nonlinear relationships between the target variable (lightning yes/no) and explanatory variables (ERA5). The most important explanatory variables have been selected objectively using a combination of stability selection and gradient boosting. This objective selection has reduced the pool of 85 potential ERA5 variables to the 9 most important ones. This reduced set still represents a large variety of processes including favorable environments for thunderstorms, charge separation and trigger mechanisms. The performance of the resulting GAM has been tested using cross-validation over the period of 2010-2019. 

Results: With the resulting GAM lightning for the Eastern Alps and their surroundings has been reconstructed over a period of four decades (1979-2019). The most intense changes occurred over the high Alps where lightning activity doubled in the past decade compared to the 1980s. There, the lightning season reaches a higher maximum and starts one month earlier. Diurnally, the peak is up to 50% stronger with more lightning strikes in the afternoon and evening hours. Signals along the southern and northern alpine rim are similar but weaker whereas the flatlands north of the Alps have no significant trend.

How to cite: Simon, T., Mayr, G. J., Morgenstern, D., Umlauf, N., and Zeileis, A.: Amplification of annual and diurnal cycles of alpine lightning over the past four decades, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1314, https://doi.org/10.5194/egusphere-egu22-1314, 2022.

09:23–09:29
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EGU22-4102
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ECS
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On-site presentation
Riccardo Hénin, Veronica Torralba, Antonio Cantelli, Enrico Scoccimarro, Stefano Materia, and Silvio Gualdi

Hail is a meteorological phenomenon with adverse impacts affecting multiple socio-economic sectors such as agriculture, renewable energy and insurance (e.g. Púčik et al., 2019; Martius et al., 2018; Macdonald et al., 2016). The mitigation of the hail-related risk in particularly sensitive regions such as Italy has fostered hail research, aiming at a deeper understanding of the favorable environmental conditions for hail formation and the improvement of hail forecasting skills (Mohr and Kunz, 2013). Nevertheless, one of the major limitations for the study of long-term hail variability is the inherent difficulty in measuring all the hail occurrences and the consequent scarce temporal and spatial coverage of hail observations (Mohr et al., 2015). Therefore, in this study, the Probability Density Functions (PDFs) of several large-scale meteorological variables and convective indices from the ERA5 reanalysis are considered instead, with the aim of describing a conditioned hail probability, following the statistical method by Prein and Holland (2018). Then, the best set of variables to be used as predictors in the hail model are selected with a machine learning approach, based on a genetic algorithm. The model output is an estimation of the hail probability over Italy in the 1979-2020 period, on a 30x30 km grid. The model is validated over the Friuli-Venezia-Giulia region through an independent dataset based on hail pads. The estimated hail probability has been used to characterize the seasonality, long-term variability and trends of the hail frequency and to investigate the potential large-scale drivers of hailstorms over Italy. 

 

REFERENCES:

Púčik, T., Castellano, C., Groenemeijer, P., Kühne, T., Rädler, A. T., Antonescu, B., & Faust, E. (2019). Large hail incidence and its economic and societal impacts across Europe. Monthly Weather Review, 147(11), 3901-3916. doi: 10.1175/MWR-D-19-0204.1.

Martius, O., Hering, A., Kunz, M., Manzato, A., Mohr, S., Nisi, L., & Trefalt, S. (2018). Challenges and recent advances in hail research. Bulletin of the American Meteorological Society, 99(3), ES51-ES54. doi: 10.1175/BAMS-D-17-0207.1.

Macdonald, H., Infield, D., Nash, D. H., & Stack, M. M. (2016). Mapping hail meteorological observations for prediction of erosion in wind turbines. Wind Energy, 19(4), 777-784. doi: 10.1002/we.1854.

Mohr, S., Kunz, M., & Geyer, B. (2015). Hail potential in Europe based on a regional climate model hindcast. Geophysical Research Letters, 42(24), 10-904. doi:10.1002/2015GL067118.

Prein, A. F., & Holland, G. J. (2018). Global estimates of damaging hail hazard. Weather and Climate Extremes, 22, 10-23. doi: 10.1016/j.wace.2018.10.004.

 

How to cite: Hénin, R., Torralba, V., Cantelli, A., Scoccimarro, E., Materia, S., and Gualdi, S.: Modelling hail probability over Italy using a machine learning approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4102, https://doi.org/10.5194/egusphere-egu22-4102, 2022.

09:29–09:35
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EGU22-7214
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ECS
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On-site presentation
Francesco Battaglioli, Pieter Groenemeijer, and Ivan Tsonesvky

An additive logistic regression model for large hail was developed based on convective parameters from ERA5 reanalysis, severe weather reports from the European Severe Weather Database (ESWD), and lightning observations from the Met Office Arrival Time Difference network (ATDnet). This model was shown to accurately reproduce the spatial distribution and the seasonal cycle of observed hail events in Europe. A spatial map of the modelled mean distribution for hail > 2 cm will be presented.

To explore the value of this approach to medium-range forecasting, a similar statistical model was developed using four predictor parameters available from the ECMWF Ensemble Prediction System (EPS) reforecasts: Mixed Layer CAPE, Deep Layer Shear, Mixed Layer Mixing Ratio and the Wet Bulb Zero Height. Probabilistic large hail predictions were created for all available 11-member ensemble forecasts (2008 to 2019), for lead times from 12 to 228 hours.

First, we evaluated the model’s predictive skill depending on the forecast lead time using the Area Under the ROC Curve (AUC) as a validation score. For forecasts up to two to three days, the model highlights a very high predictive skill (AUC > 0.95). Furthermore, the model retains a high predictive skill even for extended forecasts (AUC = 0.85 at 180 hours lead time) showing that it can identify regions with hail potential well in advance. Second, we compared the forecast spatial probabilities at various lead times with observed hail occurrence focusing on a few recent hail outbreaks. Finally, our four-dimensional model was compared with logistic models based on composite parameters such as the Significant Hail Parameter (SHP) and the product of CAPE and Deep Layer Shear (CAPESHEAR). The four-dimensional model outperformed these composite-based ones at lead times up to four days. The high AUC scores show that this model could improve short-medium range hail forecasts. Preliminary application of this approach to other convective hazards such as convective wind gusts will be presented as well.

How to cite: Battaglioli, F., Groenemeijer, P., and Tsonesvky, I.: Forecasting Large Hail Using Logistic Models and the ECMWF Ensemble Prediction System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7214, https://doi.org/10.5194/egusphere-egu22-7214, 2022.

09:35–09:41
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EGU22-10975
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ECS
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Virtual presentation
Georgios Papavasileiou, Vasiliki Kotroni, Konstantinos Lagouvardos, and Theodore M. Giannaros

On October 4, 2019, giant hailstones of 11 cm were reported in northern parts of Attica in southern Greece. During the same day, multiple large hail reports of hailstones larger than 3 cm as well as 5 tornadoes were reported in the European Severe Weather Database along the track of a long lived supercell thunderstorm that formed over northeastern Peloponnese and moved northeastwards to Attica and Euboea. In this study, we investigate the synoptic and mesoscale weather conditions that led to this rare event by using upper-air measurements from the Athens International Airport, satellite retrievals from METEOSAT, and reanalysis data from ERA5. 

Furthermore, the predictability of this rare event is studied through high-resolution simulations performed with BOLAM, MOLOCH and WRF-ARW models, which are used operationally by the METEO unit at the National Observatory of Athens. The models were able to reproduce the mesoscale environment associated with these severe weather events, showing a highly unstable environment in Saronic gulf with more than 3000 J kg-1 MLCAPE overlapped by more than 25 m s-1 0–6 km Bulk Shear. However, the models were not able to fairly reproduce the triggering, track and timing of the supercell formation highlighting the great uncertainties associated with the initiation of deep moist convection over areas with complex terrain. Here, we attempt to constrain these uncertainties by applying a diagnostic tool for predicting hail size using an ensemble of high resolution simulations and we discuss its operational usage. 

How to cite: Papavasileiou, G., Kotroni, V., Lagouvardos, K., and Giannaros, T. M.: Observational and numerical study of a giant hailstorm in Attica, Greece, on October 4, 2019, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10975, https://doi.org/10.5194/egusphere-egu22-10975, 2022.

09:41–09:47
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EGU22-8612
A gap filled procedure for the analysis of frost days in southern Italy
(withdrawn)
Ilaria Guagliardi, Tommaso Caloiero, Giuseppe Pappagallo, and Emanuele Barca
09:47–10:00
Coffee break
Chairpersons: Uwe Ulbrich, Athanasios Loukas, Maria-Carmen Llasat
Extreme precipitation and floods
10:20–10:26
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EGU22-7030
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On-site presentation
Byung-Kwon Moon, Jieun Wie, and Jinhee Kang

In East Asia, unusually long-term and heavy rainfall in 2020 resulted in concentrated socio-economic damage and flooding. In this study, the characteristics of the Madden–Julian Oscillation (MJO) related to the prediction of heavy rainfall in East Asia were analyzed using the sub-seasonal to seasonal (S2S) prediction model. In 2020, unusually high precipitation fell in East Asia, compared to an average year, for an extended time. Precipitation was concentrated from the end of June to the middle of August; therefore, the analysis was carried out with an initial model date of July 2, 2020, while the lead-time was selected 1–31 day (July 3 to August 1). The model underestimated cumulative precipitation compared to observations, with KMA and UKMO having the lowest errors and ECMWF and CMA having the largest errors. The 850-hPa position altitude and wind field anomaly was analyzed and averaged over the prediction period. The results revealed that models with large errors showed different locations for the western and northern boundaries of the high pressure in the western North Pacific region, relative to observations, or else underestimated the size of the high-pressure zone. Based on the MJO prediction phases for July in the S2S models, models with good precipitation prediction performance in East Asia mainly showed phases 1–3 that were similar to observations and their amplitudes were also large. In contrast, models with poor prediction performance exhibited fewer instances of phases 1–3 on strong days or their amplitudes were small. This suggests that if an S2S model predicts the characteristics of the MJO accurately, similar to observations, it could improve predictions of summer precipitation in East Asia.

This work was funded by the Korea Meteorological Administration Research and Development Program under Grant KMI2020-01212.

How to cite: Moon, B.-K., Wie, J., and Kang, J.: Madden–Julian Oscillation related to the prolonged heavy rainfall in East Asia in 2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7030, https://doi.org/10.5194/egusphere-egu22-7030, 2022.

10:26–10:32
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EGU22-11944
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ECS
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On-site presentation
Wazita Scott, Marco Gaetani, and Giorgia Fosser

In the last years, many countries in Europe have been experiencing an increased frequency of extreme precipitation leading to natural disasters like floods and landslides. In Italy, the majority of the country’s natural disasters have been related to extreme precipitation. Floods and landslides have led to the country experiencing great loss in its social and economic structure. Early warning systems are important to stakeholders such as Disaster Risk Managers to make informed decisions in relation to a forecasted disaster.

Extreme precipitation is often associated with specific circulation patterns. Precursor information about atmospheric circulation patterns can therefore act as an indicator of an oncoming extreme precipitation event. The objective of this work is to identify the weather circulation patterns associated with extreme precipitation events over Italy.

E-OBS precipitation datasets were used to identify the most intense extreme precipitation events for each season for the period 1990-2020 across Italy. Mean sea level pressure and 500 hPa geopotential height from the ERA5 dataset were used to identify circulation anomalies associated with the extreme events. The analysis is performed by clustering extreme precipitation events into three homogeneous climatic zones in Italy defined following the Köppen-Geiger classification.

Results show that extreme precipitation events are always associated with an intense low pressure system located within the Euro-Mediterranean region. Depending on the location of precipitation extremes across different climatic zones, low pressure location changes, also modifying the atmospheric circulation and the associated moisture transport. Namely, for precipitation extremes occurring in the Italian peninsula, the low pressure is located in central-western Europe, while for extremes in Sardinia and Sicily, low pressure is in the Mediterranean. 

How to cite: Scott, W., Gaetani, M., and Fosser, G.: Weather circulation patterns associated with extreme precipitation events in Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11944, https://doi.org/10.5194/egusphere-egu22-11944, 2022.

10:32–10:38
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EGU22-8193
Sensitivity of WRF microphysics schemes to Convective Permitting Simulation of January 2017 Heavy Rainfall Events in Southern Thailand
(withdrawn)
Yi Wang, Netsanet Alamirew, Jimy Dudhia, Changhai Liu, Cherith Moses, and Kanchana Nakhapakorn
10:38–10:44
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EGU22-7209
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ECS
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Virtual presentation
Nicole Ritzhaupt and Douglas Maraun

Heavy precipitation is a major natural hazard that can have severe impacts.  In response to global warming, the character of heavy precipitation is expected to change. Projections of the future hydrologic cycle, especially of heavy precipitation, are uncertain. Especially at the regional scale, different data sources, such as different ensembles of global and regional climate models (GCMs and RCMs), provide sometimes conflicting conclusions. Therefore, it is even more important to investigate where differences between ensembles lie and to which processes they can be attributed.

A precipitation scaling (introduced by Paul O’Gorman) is used to disentangle thermodynamic and dynamic contributions in extreme precipitation. In this work, we compare the results of CMIP5 and CMIP6 and focus on climate change signals between the periods 1971-2000 and 2071-2100 over Europe. The thermodynamic component provides homogeneous signals across Europe with a rise in extreme precipitation of about 7 %/K. In contrast, the dynamic component shows no spatial homogeneous results where the dynamic contribution can even modify the thermodynamic signal. The spread between the models within one ensemble is much larger. However, based on initial analyses, the spread in the CMIP6 models appears to have become smaller compared to CMIP5. This means, understanding the dynamic changes is the key to understanding the differences between the ensembles.

As a next step, to analyze the discrepancy between CMIP5 and CMIP6 in terms of atmospheric circulation changes, we look into three atmospheric drivers: tropical and polar amplification of global warming and changes in stratospheric vortex strength.  

How to cite: Ritzhaupt, N. and Maraun, D.: Differences in the regional pattern of projected future changes in extreme precipitation over Europe are driven by the dynamic contribution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7209, https://doi.org/10.5194/egusphere-egu22-7209, 2022.

10:44–10:50
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EGU22-4588
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On-site presentation
Kelvin S. Ng, Gregor C. Leckebusch, and Kevin Hodges

Over the past few decades, while several advancements in improving the performance of global climate models (GCMs), such as predicting mean climate,  have been made, predicting extreme rainfall events related to Mei-yu fronts (MYFs) and tropical cyclones (TCs) remains an open challenge. This is partially due the coarse spatial resolution of the GCMs that restricts their ability to represent extreme events and the associated processes on relevant spatial scales. This poses a problem for stakeholders as a failure to take appropriate precautionary action before the occurrence of extreme events can have disastrous consequences. Although the spatial resolutions of typical GCMs are too coarse to simulate extreme precipitation accurately, they are more likely to be able to simulate large-scale climate modes (LSCMs) better. Given that the activities of MYFs and TCs are linked to LSCMs, we can make use of these causal connections between LSCMs and extreme rainfall associated with MYFs/TCs to construct useful prediction models. This can then be applied to the outputs of climate GCM simulations to increase our capability in predicting extreme rainfall in the future.

In this presentation, we demonstrate a novel technique based on causality-guided statistical models (CGSMs) to assess the projected future changes of extreme rainfall associated with MYFs and TCs over China using the CMIP6 historical and SSP585 scenario simulations for four selected models. First, we show that CGSMs, which are constructed using historical observations and reanalysis, have good performance in modelling historical observations. Then we compare extreme rainfall related to MYFs/TCs from the CMIP6 historical direct output of the selected models with the CGSMs predictions. Our results show that the climatological patterns of CMIP6 direct historical outputs are different to the observed climatological patterns. Yet, CGSMs driven by CMIP6 LSCMs can produce similar patterns as the observed climatology. For the projected change under the SSP585 scenario, projections based on CGSMs provide a more coherent picture than CMIP6 direct model outputs. This shows the potential of causality-guided approach in coarse resolution climate model outputs. The implication and potential use of this approach is also discussed.

How to cite: Ng, K. S., Leckebusch, G. C., and Hodges, K.: A Causality-guided Approach for Predicting Future Changes in Extreme Rainfall over China Using Known Large-scale Modes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4588, https://doi.org/10.5194/egusphere-egu22-4588, 2022.

10:50–10:56
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EGU22-8566
Jennifer Catto, Phil Sansom, and David Stephenson

Sub-daily precipitation extremes are expected to increase in intensity in a warming climate, at a rate higher than that expected from the Clausius Clapeyron scaling. Depending on the region, these precipitation extremes can be caused by different weather system types, such as extratropical or tropical cyclones, fronts, and thunderstorms. In this study we use a storm typology, based on the objective identification of cyclone, fronts and thunderstorms, to add insight to the scaling relationship between temperature and extreme precipitation.

We use 6-hourly information on the type of weather system present at each grid box over the North Atlantic and European region from ERA5 (1981-2000) during boreal winter (DJF). The mean hourly 2-m dew-point temperature over the 6 hours closest to the weather system type, and the maximum of the hourly precipitation over the same period are then used to estimate the scaling of the precipitation extremes with temperature for each storm type. Preliminary results using quantile regression we find significantly larger scaling for weather systems including thunderstorms (greater than CC scaling) than for those that do not. We also find that for the most common weather systems over Northern Europe (front only and cyclone and front together), the scaling of extreme precipitation with temperature is below CC scaling. The future impacts of the extreme precipitation events will depend on the future changes in the frequency of different weather system types as well as the temperature scaling.

How to cite: Catto, J., Sansom, P., and Stephenson, D.: Storm-type specific scaling of sub-daily precipitation with temperature over the North Atlantic and Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8566, https://doi.org/10.5194/egusphere-egu22-8566, 2022.

10:56–11:02
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EGU22-4205
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ECS
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On-site presentation
Florian Ruff and Stephan Pfahl

Extreme, large-scale precipitation events can lead to extreme river floodings which are one of the most dangerous weather events for society when occurring in highly populated areas. However, the largest impacts are caused by very rare events with return periods on the order of 100 years. To do a quantitative and robust analysis of daily 100-year precipitation events, observational time series are typically too short. Therefore, an approach is applied here in which operational ensemble prediction data from the ECMWF are used to generate a large pool of simulated, but realistic daily precipitation events (corresponding to 1200 years of data) from which several 100-year events can be analysed. For five different major Central European river catchments, composite analyses show that 100-year precipitation events in all catchments are typically associated with an upper-level trough moving into Central Europe 24h to 48h before the occurrence of the events. During the 24h before the events, details in the progression of the trough and the location of the associated surface cyclone determine in which catchment extreme precipitation occurs. A comparison to composite analyses of less extreme precipitation events shows that dynamical mechanisms such as an amplified mid-tropospheric trough/cut off are more important for an intensification of precipitation events in the Danube and Oder catchments while in the Elbe, Rhine and Weser/Ems catchments thermodynamical mechanisms such as a larger moisture flux are more important. The question how a warmer climate will affect the dynamical processes of such extreme precipitation events will be investigated in a follow-up study.

How to cite: Ruff, F. and Pfahl, S.: Dynamical analysis of large-scale 100-year precipitation events over Central European river catchments and their differences to less extreme events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4205, https://doi.org/10.5194/egusphere-egu22-4205, 2022.

11:02–11:08
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EGU22-13038
Hadush Meresa and Conor Murphy

Climate change has a significant role in increasing extreme precipitation, including the intensity, frequency, and magnitude of events due to increases in atmospheric moisture and climate variability. This means that future increases in floods due to climate change must be considered in the construction of flood defenses, as well as the planning of new infrastructure and hydraulic structures. Previous approaches for stress testing the design of flood defenses have relied on the scenario neutral approach and the use of harmonic functions to represent changes in the seasonality and mean of precipitation. Such approaches may inadequately account for changes in extreme precipitation, especially in runoff dominated catchments. Here, we adapt the scenario neutral approach by integrating a discrete wavelet transform (DWT) to develop the flood response surface. Such an approach allows evaluation of flood sensitivity to high and low frequency components of precipitation. Using 39 catchments in Ireland, we examine the sensitivity of flooding (QT20) to changes in low and high frequency precipitation and air temperature. A sensitivity domain of 525 extreme precipitation scenarios is applied by combining 21 low frequency and 25 high frequency sets of precipitation and air temperature changes, with short duration frequency incorporated in each harmonic wavelet function. Clustering and discriminant analysis are used to create a typology of catchment sensitivity based on generated response surfaces, the mean of annual maximum precipitation, and the mean of annual maximum flows. Results allow characterization of catchment sensitivity in gauged and ungauged locations and the integration of a wider spectrum of precipitation changes when assessing sensitivity allowances for climate change.  

 

How to cite: Meresa, H. and Murphy, C.: Evaluating flood sensitivity to changes in high and low frequency precipitation using a discrete wavelet transform , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13038, https://doi.org/10.5194/egusphere-egu22-13038, 2022.

11:08–11:14
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EGU22-3090
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ECS
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On-site presentation
Faizal Immaddudin Wira Rohmat, Ioanna Stamataki, Zulfaqar Sa'adi, and Djelia Fitriani

Flooding is a natural disaster with extremely wide-reaching impacts and is a recurring problem in Indonesia. Whilst possible impacts of climate change are expected to aggravate flood risk in already flood-vulnerable areas, many countries struggle to achieve the United Nations’ (UN) 2030 Sustainable Development Goals (SDGs) to achieve a better and more sustainable future for all. Using the case study of Majalaya, Indonesia, the authors investigated the impact of climate change and climate variability on urban flood risk through science-based spatio-temporal flood simulations. Based on the ensemble of 17 General Circulation Models (GCMs) CMIP6, the near-future (2021 to 2050) flood projection under Shared Socioeconomic Pathways (SSPs) 2.6 (low forcing), 4.5 (medium forcing) and 8.5 (high end forcing) common to historical (1981 to 2014) was simulated. The area’s future risk of flooding was then investigated and adaptation measures were suggested for reducing and mitigating worsening flood conditions. A numerical model was developed in HEC-RAS that represented the city of Majalaya and the results were combined with the ensemble of climate projections to enable the assessment of the effects of flooding due to the combined effect of climate change and urbanisation. The model was calibrated using historical stream gauge records and past extreme flood inundation boundaries. Using the model’s output metrics (e.g. flood depth, velocity) and local demographic data, the project aims then to use a vulnerability assessment framework to quantify the impact of climate change on flood risk. The modelling results will allow for spatio-temporal mapping of the flood-prone areas in Majalaya, which will help reduce risk and vulnerability for disadvantaged populations. The development of flood vulnerability maps and future flood risk projections will assist the government in developing land-use and flood prevention management policies. This research area, drawing from the combination of flood modelling and the use of climate projections, allows for an assessment of future flood risk scenarios of the city of Majalaya and paves new avenues towards future research.

How to cite: Rohmat, F. I. W., Stamataki, I., Sa'adi, Z., and Fitriani, D.: Flood analysis using HEC-RAS: The case study of Majalaya, Indonesia under the CMIP6 projection, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3090, https://doi.org/10.5194/egusphere-egu22-3090, 2022.

11:14–11:20
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EGU22-5815
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ECS
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On-site presentation
Pablo López, Liz Holcombe, Katerina Michaelides, and Jeremy Phillips

Extreme rainfall events are increasing the frequency of hydrological hazards such as landslides, debris flow, and erosion processes. Understanding the coupling of these hazards is still a challenging task, current methodologies often take a single hazard approach without integrating the mechanisms that describe the influence of one hazard on another under the same rainfall event. Physically-based distributed models have overcome these limitations incorporating the coupling of hillslope-hydrological processes that influence the interactions of hydrological hazards at the catchment scale. Nonetheless, within these models, the physical characteristics of the catchment domain are subject to a large spatial variability increasing the uncertainty in the parameters that influence the interaction of these hazards, hindering their representation in data-scarce catchments. The aim of this study is to elaborate an experimental design to parameterize a physically-distributed model to identify the parameters that have an acceptable influence in representing and describing hydrological hazard interactions under a data-scarce environment.

The study area is set in the Soufriere catchment in Saint Lucia, which recorded multiple landslides and debris flows with impacts on catchment erosion triggered by Hurricane Tomas in October 2010. The OpenLISEM model was used to estimate the parameters that influenced the triggering of hydrological hazards that occurred during Hurricane Tomas. The parameter estimation was performed through a Global Sensitivity Analysis (GSA) All-At-a-Time (ATT) to assess simultaneously under 144 simulations the estimation of hydrological and geotechnical parameters. The parameters subject to Sensitivity Analysis were saturated moisture content, saturated hydraulic conductivity, soil cohesion, and internal friction angle. The results were verified through the Sorensen-Dice coefficient. The coefficient was calculated through a spatial overlapping method between landslide simulated areas and landslide inventory areas corresponding to the Hurricane Tomas triggered landslides obtained from the British Geological Survey (2014). The results indicated that the representation of landslides, debris flows, and erosion processes on the OpenLISEM model highly depend on the quality of the input data. The latter was confirmed by the Sorensen-Dice coefficient indicated low spatial overlap values between the simulations performed. Nevertheless, the response of the OpenLISEM model to an acceptable landslide representation similar to the landslides triggered by Hurricane Tomas was influenced in the first place by the soil cohesion and internal friction angle and in the second place by the saturated moisture content and saturated hydraulic conductivity. The identification of these parameters introduces an improvement to provide an acceptable representation of hydrological hazards interactions given the data available in a data-scarce environment.

How to cite: López, P., Holcombe, L., Michaelides, K., and Phillips, J.: Parameter exploration for hydrological hazard interactions in a data-scarce catchment., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5815, https://doi.org/10.5194/egusphere-egu22-5815, 2022.

11:20–11:26
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EGU22-6503
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On-site presentation
Elena Toth, Mattia Neri, Alfredo Reder, and Guido Rianna

The evaluation of the resilience of flood protection systems requires the assessment of the impact of climate change scenarios on future flood regimes. Due to the high computational effort and to the scarcity of hourly climate modelling chains, expected changes in future floods are often simulated by hydrological models on a daily basis, even for basins with short response times, where hourly simulations would be needed.

In this work, the expected occurrence and magnitude of future flood events is modelled through the coupling of bias-corrected local climate scenarios at hourly time scale and continuous rainfall-runoff modelling, in reference to the Panaro river (one of the OpenAir Laboratories in the OPERANDUM H2020 project), a tributary of the Po River in the Apennines.

The investigation exploits hourly precipitation and daily max/min temperature (used for interpolation at hourly scale) timeseries for a subset of climate modelling chains included in the EURO-CORDEX initiative through the dynamical downscaling of Global Climate Models under the RCP 8.5 concentration scenario. The comparison with observed spatial fields obtained from weather stations and from gridded E-OBS products allows to assess the biases affecting the climate raw data.

The Scaled Distribution Mapping (SDM) bias correction procedure (Switanek et al. 2017), that preserves raw climate model projected changes in the bias-corrected series, is then applied to adjust the raw model output towards observations.

A semi-distributed, continuously simulating rainfall-runoff model is parameterised on the basis of the observed meteorological and streamflow time-series, especially focusing on the reproduction of past flood events. The model is then run to reproduce the continuous hourly streamflow time-series in the Panaro river over past and future decades, providing in input i) observed meteorological forcing based on ground stations, ii) raw and bias-corrected climate scenarios over the control period, iii) bias-corrected climate scenarios for the future decades. Finally, the flood events are extracted from the continuous streamflow simulations and the changes in the flood signals expected over the future decades are analysed, in terms of both peaks and volumes.

 

References

Switanek, M. B., Troch, P. A., Castro, C. L., Leuprecht, A., Chang, H.-I., Mukherjee, R., and Demaria, E. M. C.: Scaled distribution mapping: a bias correction method that preserves raw climate model projected changes, Hydrol. Earth Syst. Sci., 21, 2649–2666, https://doi.org/10.5194/hess-21-2649-2017, 2017.

How to cite: Toth, E., Neri, M., Reder, A., and Rianna, G.: Future occurrence and magnitude of flood events in the Panaro River (Northern Italy): coupling bias-corrected hourly climate scenarios and semi-distributed rainfall-runoff modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6503, https://doi.org/10.5194/egusphere-egu22-6503, 2022.

11:26–11:32
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EGU22-9985
Pedro Costa and the RV Meteor M-152 scientific team

In the present climate change scenario, the perception regarding the frequency and magnitude of flood events is changing. Nevertheless, to establish return periods and flooding patterns it is important to expand the time-window of observation beyond the historical period. To achieve this purpose, it is crucial to use the sedimentological record of alluvial plains and river banks. However, anthropogenic activities have disrupted the sedimentary dynamics thus interfering with the geomorphological settings and their stratigraphy’s. An alternative setting is the shallow nearshore, below storm wave base, where potentially stratigraphy is better preserved.

After a campaign on board RV Meteor, a group of sediment cores were collected offshore the south Portuguese coast. These cores cover the Holocene Epoch and consist essentially on alternations of silty bioclastic layers with some sandy units rich in quartz and bioclasts. The vertical variation of several sedimentological proxies allowed the differentiation of disruptive events, mostly related with extreme marine inundations or possibly linked with abrupt fluvial discharges.

Here we present some preliminary results based on grain-size and compositional analysis (XRD) and attempt to establish a chronology of those events. The preliminary data interpretation seems to suggest an increase in the flood record over the last 1000 years. However, this observation needs further support from other locations in the area and also requires a better understanding of post-depositional processes that affect the record of thin muddy layers on the nearshore stratigraphy.

 

This work was supported by projects OnOff - PTDC/CTAGEO/28941/2017 – financed by FCT. and FCT/UIDB/50019/2020 - IDL, also funded by FCT.

How to cite: Costa, P. and the RV Meteor M-152 scientific team: Flood sedimentological records off the south Portuguese coasts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9985, https://doi.org/10.5194/egusphere-egu22-9985, 2022.

11:32–11:50
Lunch break
Chairpersons: Piero Bellanova, Catrina Brüll, Maria-Carmen Llasat
Droughts-Impacts of extreme events-Τhe July 2021 flood event
13:20–13:26
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EGU22-1843
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Virtual presentation
Renata Libonati, João L Geirinhas, Patrícia S Silva, Ana Russo, Julia A Rodrigues, Liz B C Belem, Joana Nogueira, Fabio O Roque, Carlos C DaCamara, Ana M B Nunes, Jose A Marengo, and Ricardo M Trigo

The year of 2020 was characterised by an unprecedented fire season in Pantanal, the largest continuous tropical wetland, located in south-western Brazil. This event was the largest ever recorded over, at least, the last two decades, reaching an amount of 3.9 million ha and affecting 17 million vertebrates1,2. Recent evidence points out that this event resulted from a complex interplay between human, landscape, and meteorological factors3,4. Indeed, much of the Pantanal has been affected by severe dry conditions since 2019, with 2020’s drought being the most extreme and widespread ever recorded in the last 70 years5,6. The drought condition was maintained at record levels during most of the year of 2021, following the climate change scenarios expected for this region7. Prior to this comprehensive assessment, the 2020’s fire season has been analyzed at the univariate level of a single climate event, not considering the co-occurrence of extreme and persistent temperatures with soil dryness conditions. Here, we show that the influence of land–atmosphere feedbacks contributed decisively to the simultaneous occurrence of dry and hot spells, exacerbating fire risk. These hot spells, with maximum temperatures 6 ºC above-average were associated with the prevalence of the ideal synoptic conditions for strong atmospheric heating, large evaporation rates and precipitation deficits4. We stress that more than half of the burned area during the fire season occurred during compound drought-heatwave conditions. The synergistic effect between fuel availability and weather-hydrological conditions was particularly acute in the vulnerable northern forested areas. These findings are relevant for integrated fire management in the Pantanal as well as within a broader context, as the driving mechanisms apply across other ecosystems, implying further efforts for monitoring and predicting such extreme events.

 

References

[1] Garcia, L.C, et al.. Record-breaking wildfires in the world’s largest continuous tropical wetland: Integrative fire management is urgently needed for both biodiversity and humans. J. Environ. Manage. 2021, 293, 112870.

[2] Tomas, W. M., et al. Counting the dead: 17 million vertebrates directly killed by the 2020’s wildfires in the Pantanal wetland, Brazil. Sci. Rep. accepted.

[3] Libonati, R.; et al. Rescue Brazil’s burning Pantanal wetlands. Nature. 2020, 588, 217–219.

[4] Libonati, R., et al. Assessing the role of compound drought and heatwave events on unprecedented 2020 wildfires in the Pantanal. Environmental Research Letters. 2022, 17, 1.

[5] Thielen, D., et al. The Pantanal under Siege—On the Origin, Dynamics and Forecast of the Megadrought Severely Affecting the Largest Wetland in the World. Water. 2021, 13(21), 3034.

[6] Marengo, J.A., et al. Extreme Drought in the Brazilian Pantanal in 2019–2020: Characterization, Causes, and Impacts. Front. Water. 2021, 0, 13.

[7] Gomes, G.D.; et al.. Projections of subcontinental changes in seasonal precipitation over the two major river basins in South America under an extreme climate scenario. Clim. Dyn. 2021, 1-23.

 

This work was supported by Project Rede Pantanal from the Ministry of Science, Technology and Innovations of Brazil (FINEP grant 01.20.0201.00). R.L. was supported by CNPq [grant 305159/2018–6] and FAPERJ [grant E26/202.714/2019]

How to cite: Libonati, R., Geirinhas, J. L., Silva, P. S., Russo, A., Rodrigues, J. A., Belem, L. B. C., Nogueira, J., Roque, F. O., DaCamara, C. C., Nunes, A. M. B., Marengo, J. A., and Trigo, R. M.: The impact of compound drought and heatwave events on the unprecedented 2020 fire season in the Pantanal, Brazil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1843, https://doi.org/10.5194/egusphere-egu22-1843, 2022.

13:26–13:32
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EGU22-4353
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ECS
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On-site presentation
Iván Noguera, Fernando Domínguez-Castro, and Sergio M. Vicente-Serrano

Flash droughts are distinguished by a rapid development and intensification, which increase the potential drought impacts on natural and socio-economic systems. In recent years, a great effort has been made to identify and quantify this type of events in different regions of the world using different metrics. We developed a methodology to analyze the flash droughts based on SPEI at short-time scale (1-month) and high-frequency data (weekly). Thus, we characterized the occurrence of flash drought in Spain over the period 1961-2018 and showed that flash drought is a frequent phenomenon (40% of all droughts were characterized by rapid development), which exhibit a great spatiotemporal variability. The northern regions, where a higher frequency of flash droughts was found, showed negative trends in the frequency of flash droughts, while the central and southern regions subject to fewer flash drought events showed generally positive trends. Usually, the flash drought is associated with severe precipitation deficits and/or anomalous increases in atmospheric evaporative demand (AED), but while the role of precipitation seems obvious and essential, the role played by AED in triggering or reinforcing flash drought episodes is much more complex and exhibits important spatial and temporal contrasts. In Spain, the effect of AED is mainly restricted to water-limited regions and the warm season, but its role is minimal in energy-limited regions and in cold periods in which precipitation deficits are the main cause of flash drought development. However, the contribution of the AED on the development of flash droughts has increased notably over the last six decades, thus becoming a decisive driver in explaining the occurrence of the latest flash droughts in some regions of Spain. These findings have strong implications for proper understanding of the recent spatiotemporal behavior of flash droughts in Spain and illustrate how this type of event can be related to global warming processes.

How to cite: Noguera, I., Domínguez-Castro, F., and Vicente-Serrano, S. M.: How does the rise of atmospheric water demand affect flash drought development in Spain?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4353, https://doi.org/10.5194/egusphere-egu22-4353, 2022.

13:32–13:38
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EGU22-9831
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On-site presentation
Efi Rousi, Andreas Fink, and Laura Suarez-Gutierrez and the ClimXtreme project

The summer of 2018 was an extraordinary extreme season in Europe bringing simultaneous, widespread and coherent extremes of heat and drought in large parts of the continent with extensive impacts on agriculture, forests, water supply, and large financial losses. Joining different areas of expertise available within the German ClimXtreme project (https://www.climxtreme.net/index.php/en/), we present a comprehensive analysis of the 2018 extreme European summer in terms of heat and drought.

First, we define the events using different traditional, as well as, novel metrics. Then, we present a comprehensive dynamical analysis of the background atmospheric state, in order to better understand the events by bringing together different approaches. First results indicate that the summer of 2018 was characterized by persistent NAO+ conditions, which favored the occurrence and persistence of a Eurasian double jet stream structure. Both of those features contribute to the occurrence of heat extremes in western and central Europe. Additionally, positive blocking frequency anomalies were present over Scandinavia, which favored the intense heatwave in the region. An analysis of Rossby wave activity during the 2018 summer shows an eastward propagation of Rossby wave packets from the Pacific towards the Atlantic and the European continent already at the end of June and before the initiation of the heatwave over Scandinavia. When the peak over the Iberia occurs, there is no pronounced Rossby wave activity, which highlights the different mechanisms involved, i.e., subtropical ridges and Saharan air intrusions.

Low-frequency precursors, such as SSTs and soil moisture in spring, and their role in shaping those extreme events are also analyzed. A conspicuous tripolar SST anomaly pattern over the N. Atlantic, consisting of a cold blob south of Greenland and Iceland, was prominent starting in early spring. At the same time, a severe soil moisture depletion over Germany between April and July reflects the persistently warm and dry conditions in spring 2018 that caused anomalously dry soils in summer.

Last but not least, a tailored attribution study is presented, comparing the 2018 central European heatwave with similar events in the MPI Grande Ensemble and in CMIP6 models. To provide tailored information for this study, the event was defined as the maximum daily temperature in Germany averaged over different lengths of periods of consecutive days to account for the prolonged heat that characterized the summer of 2018. According to the MPI-GE almost every summer will be more extreme than 2018 under a 2˚C warmer world.

As heat and drought conditions are likely to become more frequent and intense under anthropogenic climate change, we argue that the scientific community can benefit from such comprehensive and transdisciplinary studies.

How to cite: Rousi, E., Fink, A., and Suarez-Gutierrez, L. and the ClimXtreme project: A comprehensive study of the extreme heat and drought of the 2018 European summer , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9831, https://doi.org/10.5194/egusphere-egu22-9831, 2022.

13:38–13:44
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EGU22-359
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ECS
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Virtual presentation
Dipesh Chapagain, Luna Bharati, and Christian Borgemeister

Human mortality and economic losses due to climatic disasters have been rising globally. Several studies argue that this upward trend is due to rapid growth in the population and wealth exposed to disasters. Others argue that rising extreme weather events due to anthropogenic climate change are responsible for the increase. Hence, the causes of the increase in disaster impacts remain elusive. Disaster impacts are higher in low-income countries, but existing studies are mostly from developed countries or at the cross-country level. This study will assess the attribution of rising climatic disaster mortality to indicators of climatic hazards, exposure, and vulnerability at the subnational scale in a low-income country, using Nepal as a case study. 
This empirical study at the scale of 753 local administrative units of Nepal will follow a regression-based approach that will overcome the limitations of the commonly used loss normalization approach in studying the attribution of disaster-induced loss and damage.

In Nepal, landslides and floods account for more than two-thirds of the total climatic disaster mortality. Hence, we will use the past 30 years (1991-2020) landslides and floods mortality data from DesInventar and Nepal's Disaster Risk Reduction portal as the dependent variable. As explanatory variables to represent climatic hazards, we will estimate and use mean and extreme precipitation indices from observational data by the Department of Hydrology and Meteorology Nepal. We will use the local unit’s population as a proxy of disaster exposure. Socio-economic and environmental indicators such as annual per capita income, percentage of people with access to mobile phones and internet, land cover distribution, and slope will be used as indicators of vulnerability. Exposure and vulnerability indicators data will be accessed from Nepal’s Central Bureau of Statistics and other sources. This study is expected to identify indicators of climatic hazards, exposure, and vulnerability that could explain the spatial and temporal variability of climatic disaster mortality in Nepal. Similarly, it will provide new insights on the role of climate change on rising climatic disaster mortality from the low-income countries’ context.

How to cite: Chapagain, D., Bharati, L., and Borgemeister, C.: Is climate change to blame for rising climatic disasters mortality in Nepal?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-359, https://doi.org/10.5194/egusphere-egu22-359, 2022.

13:44–13:50
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EGU22-11093
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ECS
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On-site presentation
Shaini Naha, Miguel Angel Rico Ramirez, and Rafael Rosolem

The serious hydrological consequences of climate change faced by developing countries like India show regional variability. Understanding these regional hydrologic impacts has a crucial role in the management of water resources. Mahanadi river basin (MRB) is a major large-scale river basin in India that is predicted to face severe floods under future climate change scenarios. Commonly, climate change impacts are simulated for a specific decade, specific scenario, or specific climate model in the future. We, however, employed an arguably more objective, approach that would identify the impacts of all possible combinations of specific change within the possible mean annual temperature and precipitation 2-dimensional scenario space (derived from thirteen CMIP6 models) on the hydrological responses. CMIP6 is the recent generation of climate models, released to overcome the drawbacks of the previous generation CMIP5 models such as under/overestimating the monsoon characteristics over the Indian subcontinent. Our methodological approach also involves using an ensemble of VIC models, representing the overall model uncertainty due to parameter value choices, in conjunction with these climate projections, instead of using a single calibrated model to predict the hydrological responses. The climate projections show an overall change in mean annual precipitation and mean annual average temperature that ranges from -5 to +105% and 0-7◦C respectively. This has resulted in significant changes in both mean annual flows and peak flows of up to 2849 and 29,776 m3s-1 respectively. Uncertainties associated with the model parameters, of up to 1211 m3s-1 are observed in the predicted peak flow magnitudes, which is considerably higher than in predicted annual flow magnitudes. Our findings indicate that precipitation mainly controls the future predicted flows in the basin. This study has provided a set of results on the likely future behavior of the MRB mean annual and peak flows under the CMIP6 climate projections. Future projections of hydrologic variables, along with the associated model parameter uncertainties can help with better hydrologic impact assessment and developing adaptation strategies for MRB in India.

Keywords: Climate change, CMIP6, VIC, Mahanadi river basin, flows

How to cite: Naha, S., Rico Ramirez, M. A., and Rosolem, R.: Quantifying the hydrological responses of future climate changes on a large scale river basin in India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11093, https://doi.org/10.5194/egusphere-egu22-11093, 2022.

13:50–13:56
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EGU22-7449
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ECS
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Virtual presentation
Paolo Tamagnone, Enrica Caporali, and Alessandro Sidoti

Humankind is currently living in an era governed by continuous climate warm-up and unstoppable urbanization, in which the ongoing climate change is leading to an exacerbation of hydrometeorological events. With an intensification of magnitude and frequency of extreme rainfall events, engineers and scientists are striving to develop methodologies and strategies to effectively defend people and assets from pluvial flooding. Pluvial floods produced by local, intense, and fast rainstorms cause the surcharge of urban drainage systems inducing the inundation of streets and buildings before the runoff reaches the receptor watercourse. Pluvial flood damage has been defined as an ‘invisible hazard’ but it increasingly weighs on the budget of direct flood losses, raising the costs incurred by flood damages. Besides the tangible losses, the costs may be even higher when the intangible share is considered, such as the potential loss of heritage held in ancient towns. For this reason, the inestimable cultural and artistic heritage preserved in historical buildings require a high-level of protection against hazards induced by natural calamities. The present study investigates extreme rainfall-related impacts and hazards threatening the cultural heritage situated in the most vulnerable areas of the Santa Croce district (Florence, Italy). The district hosts some of the most important buildings of the city: the National Central Library of Florence and the Opera di Santa Croce. The geographical location of this monumental complex makes the cultural heritage guarded inside of it dangerously exposed to multiple sources of flood hazard. Firstly, river flooding due to the proximity to the Arno River (this area has been already harshly damaged by the catastrophic flood in 1966). Secondly, flooding by sewage since that the internal drainage network is linked with one of the main sewer conduits of the city. Then, surface runoff flowing down from the headwater. Considering this framework, the pluvial flood hazard assessment is performed using a 1D/2D dual drainage model specifically implemented to simulate all hydraulic phenomena occurring both on the surface and through the sewer network. The analysis comprehends a series of scenarios designed to simulate the impact of hydrometeorological extremes on the study area and each possible concatenation of consequences or failures. The hydraulic model incorporates different layers of information: the high-resolution digital surface model of the area and buildings, the public sewer network, and the internal rainfall collection system of the district. Geometrical features and technical specifications of the sewer network have been retrieved from detailed field surveys and research in historical archives. Model’s outcomes allow identifying the critical nodes within the drainage network, delineating the most vulnerable areas, and prioritizing the rescue efforts in case of severe cloudbursts. Results may help site managers to improve the efficiency of their hazard management and emergency plans. Furthermore, the study intends to propose suitable technical solutions for safeguarding the cultural heritage where designing intrusive engineering works hardly fits within the historical urban context.

How to cite: Tamagnone, P., Caporali, E., and Sidoti, A.: Safeguarding heritage sites from hydrometeorological extremes: the Santa Croce district in Florence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7449, https://doi.org/10.5194/egusphere-egu22-7449, 2022.

13:56–14:02
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EGU22-12481
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ECS
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Virtual presentation
Luisa Bellanova, Piero Bellanova, Jan Schwarzbauer, Frank Lehmkuhl, Philipp Schulte, and Klaus Reicherter

With a projected increase in frequency and magnitude of extreme weather events, the fast-growing coastal population centers of the Asian Global South experience a higher susceptibility to flood-related pollution. This is fueled by rapid land-use changes, urbanization, a multitude of emission sources, as well as anthropogenic- and flood-induced remobilization and relocation of pollutants. To yield a more comprehensive understanding of riverine and coastal floods in conjunction with these rapid urban and land-use changes, their impact on the environment and the health risks posed to local communities, sedimentary archives need to be studied.

Meandering through densely populated urban areas, Chennai’s rivers (Cooum and Adyar) and coastal systems have been affected by monsoon-induced floods (e.g., 2015 South Indian floods) and the 2004 Indian Ocean tsunami. Simultaneously, Chennai experienced an explosive population growth over the past 30 years, with the coinciding changes in land-use, urbanization, anthropogenic alterations to aquatic systems (e.g., damming, dredging), and (unregulated) environmental pollution. Especially the missing regulations, as well as growing volumes of sewage and physical waste have an enormous toll on the aquatic systems, but also pose threats by remobilization during floods.

To investigate potential flood-induced strata and chemostratigraphic changes over time, a total of nine sediment profiles along the Adyar and Cooum rivers are subject to GC-MS analyses of organic pollutants in correlation to stratigraphic changes in the obtained sediment profiles.

First results indicate that organic pollutants, such as petrogenic compounds (hopanes, PAHs), urban wastewater compounds (LABs, DEHA, methyl-triclosane), technical compounds (Mesamoll®, DPE, NBFA) and pesticides (e.g., DDX) allow for the identification of past flooding events and their characterization in terms of release and distribution of pollution. These proxies are used to assess (chemo-)stratigraphical alterations preserved in these sedimentary archives. However, sedimentary archives in fast-growing, urbanized environments are influenced by physical anthropogenic alterations leading to superimpositions or a hiatus in the sedimentary archives, thus hampering with the (chemo-)stratigraphic reconstruction of past flooding events and environmental changes.

How to cite: Bellanova, L., Bellanova, P., Schwarzbauer, J., Lehmkuhl, F., Schulte, P., and Reicherter, K.: Chennai’s urban river systems – environmental changes, anthropogenic pollution and flood-induced remobilization, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12481, https://doi.org/10.5194/egusphere-egu22-12481, 2022.

14:02–14:08
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EGU22-11221
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ECS
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On-site presentation
Imme Benedict, Florian Polak, Thomas Vermeulen, and Chris Weijenborg

From the 12th to the 15th of July 2021, Western Europe was confronted with an abnormal amount of precipitation leading to extreme floods and enormous damage in western Germany, Belgium, Luxembourg and the Netherlands. Locally, almost thrice as much as the monthly precipitation amount was observed, up to 175 mm in two days. The large-scale weather pattern in Western Europe was characterised by an intense and stationary upper-level cut-off low.

In this study the atmospheric conditions resulting in this extreme precipitation are investigated, with a focus on understanding the enhanced moisture supply leading to the extreme precipitation amounts. Previous to the event, the Baltic area experienced a significant heatwave, and it was hypothesized that due to high evaporation rates more humid air over this region would be transported towards western Europe to result in these enormous amounts of rain.

We analysed the moisture origin of the extreme precipitation with the Lagrangian trajectory diagnostic LAGRANTO applied to both re-analysis data (ERA5) and simulations with the non-hydrostatic weather research and forecasting model (WRF). Both models represent the case rather well. In addition, the impact on precipitation by adapting the sea surface temperature (SST) of both the Baltic and the Mediterranean Sea was studied using WRF. This analysis showed that SST changes in the Mediterranean had the largest impact on precipitation in western Europe. Furthermore, first results indicate that the Mediterranean Sea, which had a positive SST anomaly of 2˚C, was the main moisture source preceding the precipitation event, contrasting our initial hypothesis.

How to cite: Benedict, I., Polak, F., Vermeulen, T., and Weijenborg, C.: Moisture origin of the extreme precipitation event in Western Europe in July 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11221, https://doi.org/10.5194/egusphere-egu22-11221, 2022.

14:08–14:14
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EGU22-9520
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On-site presentation
Michael Dietze, Rainer Bell, Thomas Hoffmann, and Lothar Schrott

Valley confined floods are a major hazard. In contrast to large river floods with day long warning time, they can evolve within minutes to hours, exhibit higher flow velocities and drive large amounts of debris into populated places. While many Alpine communities have developed mitigation, early warning and rapid response schemes for this natural hazard type, these measures are virtually unknown in Central European upland regions. Beyond flood protection, lacking measurement infrastructure also prevents retrospective collection of event anatomy data, which would be key to understand the evolution of an event and, hence to improve our response to future hazards.

The 14–15 July 2021 flood that hit the Ahr valley in the Eifel mountains, west Germany, was a drastic example of the potential of such valley confined floods. A wall of water flushed through the deeply incised valley, flooding more than 15 towns and affecting 42,000 people, resulting in the highest number of casualties in Germany since 1962. All gauges along the main channel were destroyed while the flood hydrograph was still on the rising limb and grid power loss interrupted collection and transmission of data from other potential sensors.

Here, we use data from a single seismic station near the town of Ahrweiler, originally deployed for earthquake seismology. Despite grid power cutoff around 23:19 CEST, the station recorded the arrival of the fast rising limb of the flood. We show how even an incomplete record of a single station not set up for flood early warning can be used to infer crucial and timely information about the flood: propagation velocity, water level and debris transport rate. We argue that installing a network of a few distributed low cost seismic sensors could have improved flood early warning and near real time provision of kinetic flood data. More importantly, such a network would be the key for improved response actions for future floods, deemed more likely in Central Europe under the currently changing climate conditions.

How to cite: Dietze, M., Bell, R., Hoffmann, T., and Schrott, L.: The seismic footprint of the devastating July 2021 Ahr Valley flood, Germany, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9520, https://doi.org/10.5194/egusphere-egu22-9520, 2022.

14:14–14:20
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EGU22-2312
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ECS
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On-site presentation
Joel Mohren, Matthias Ritter, Steven A. Binnie, and Tibor J. Dunai

Although fluvial erosion is predominantly governed by surface driven fluvial incision, more exotic erosional processes can significantly contribute to the fluvial shaping of landscapes. To this group belongs sapping caused by concentrated groundwater discharge, which can form a very distinct type of topography (characterised e.g. by the development of theatre-shaped channel heads). Fluvial erosion through sapping occurs where groundwater encounters a rapid change in elevation (i.e. across scarps, cliffs), and it is highly modulated by the physical properties of the solid. Groundwater sapping is, for example, promoted by inhomogeneities of permeability and/or lithological composition of the subsurface, which is often prevalent in sedimentary deposits and along contact boundaries between different lithological units. Consequently, topography shaped by groundwater sapping can be found in many places on Earth and even on Mars, and the formation of these landscapes can integrate over thousands to millions of years. However, in some regions, such as coastal areas, groundwater sapping has been reported to be associated with severe soil loss and high erosion rates on the order of tens of metres per day.

A similar magnitude of soil loss could be observed close to the village of Erftstadt-Blessem, Germany, as caused by severe flooding, peaking the 15th of July 2021. Here, intense rain events caused the formation of local drainage networks towards a gravel pit located to the north of the village. As a consequence, adjacent arable land was subject to intense backward incision, thereby eroding the underlying Quaternary sediments. The erosion formed drainage networks that appear to resemble characteristic groundwater sapping. This fluvial topography was largely preserved after the flooding, thus providing the opportunity to decipher the processes involved in the formation of these features. We use Structure-from-Motion Multi-View Stereo (SfM-MVS) photogrammetry to reconstruct the drainage geometry based on drone imagery (provided by the Kreisverbindungskommando Köln, M. Wiese; additional SfM-MVS photogrammetry data provided by ESRI Deutschland GmbH, T. Gersthofer) and photographs taken in the field using a handheld camera. The data is subsequently used to characterise the drainage networks and to compare the topography to other groundwater sapping landscapes on Earth and on Mars. Additionally, we intend to perform grain size analyses of the different sediment layers and to quantify fallout 239+240Pu in selected samples to asses the physical properties of the substratum and to trace the fate of the radionuclides during the flood event. Our aim is that our data will contribute to a better understanding of how groundwater sapping processes operate over time and to assess the importance of individual factors (e.g. substrate properties, vegetation cover and -type) on the severity of erosion. The outcome could thus not only be important for modelling terrestrial and extra-terrestrial processes but has also practical applications to the loss of arable land and the effects of outburst flooding.

How to cite: Mohren, J., Ritter, M., Binnie, S. A., and Dunai, T. J.: Erosion of arable land during the July 2021 flood event in Erftstadt-Blessem, Germany: understanding groundwater sapping, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2312, https://doi.org/10.5194/egusphere-egu22-2312, 2022.

14:20–14:26
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EGU22-5114
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Highlight
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Virtual presentation
Frank Lehmkuhl, Verena Esser, Philipp Schulte, Alexandra Weber, Stefanie Wolf, and Holger Schüttrumpf

Extreme precipitation and discharge between July 13th and 16th 2021 caused serious flooding with bank erosion, including damages to infrastructure and buildings nearby the Eifel mountain region. Especially the small town of Stolberg and Eschweiler in the Inde River catchment were heavily affected. On-site investigation along the Inde River and its tributary, the Vichtbach creek, after the flood event show that mainly coarse sediments were remobilized and accumulated in the upper and middle reaches. The water masses mobilized not only sediments including gravel but also large objects like broken down trees and cars. In contrast, silty sediments were deposited in the lower reaches.

The Stolberg region is a former mining area with related industries resulting in contaminated soils and tailings close to the floodplains (Esser et al. 2020). Therefore, our investigations also focus on pollution by sediment-bound heavy metals and their distribution in the floodplains before and after this event. Flood sediment samples were taken immediately after the extreme flood event. Based on the results of flood-related pollution monitoring, conducted between 2016 and 2019 (Esser, 2020), the impact of the extreme event in July can be evaluated. During the July flood event, an exceptional amount of pollutants was remobilized. In addition to an increase in pollutants on the modern floodplain, wider areas of older and higher floodplains (Altauen) were also affected.

Esser, V. (2020): Untersuchungen zur fluvialen Morphodynamik und zur rezenten Schadstoffausbreitung in Flusssystemen - Beispiele aus der Grenzregion Belgien, Niederlande und Deutschland. PhD-Thesis, RWTH Aachen University.

Esser, V., Buchty-Lemke, M., Schulte, P., Podzun, L.S., Lehmkuhl, F. (2020): Signatures of recent pollution profiles in comparable Central European rivers - Examples from the International River Basin District Meuse. Catena 193: 104646. https://doi.org/10.1016/j.catena.2020.104646

How to cite: Lehmkuhl, F., Esser, V., Schulte, P., Weber, A., Wolf, S., and Schüttrumpf, H.: Sediment pollution and morphodynamics of an extreme event: Examples from the July 2021 flood event from the Inde River catchment in North Rhine-Westphalia , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5114, https://doi.org/10.5194/egusphere-egu22-5114, 2022.

14:26–14:32
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EGU22-12558
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ECS
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Virtual presentation
Christina Schwanen, Piero Bellanova, and Jan Schwarzbauer

Due to extreme precipitation and runoff, severe flooding occurred in Germany in the summer of 2021 (July 13th–16th). In the catchment area of the Rur river, especially along its tributaries Inde and Wurm, but also along the Rur itself, this flood caused severe destruction and impacts on modern and older floodplains and anthropogenic utilized areas. This led to the acute and unusual input of harmful organic pollutants, as well as the remobilization and relocation of old burdens.

Particularly floodplains are of central importance during such flood events as their natural functions include water, sediment, and nutrient retention, as well as the self-purification of water bodies. The focus of this investigation was therefore on the importance and relevance of natural floodplains during and after the 2021 summer flood. For this purpose, 16 different floodplains distributed throughout the Rur’s course were sampled immediately after the flood. The objectives were to determine pollutant concentrations, distribution, and accumulation, as well as the identification of potential pollution sources. In this context, the results of previous floodplain sampling and regular monitoring of the river’s sediments are also considered.

Preliminary results indicate elevated concentrations of several organic pollutant groups, including PAHs (polycyclic aromatic hydrocarbons), PCBs (polychlorinated biphenyls), and LABs (linear alkylbenzenes). These substances are indicators of petrogenic pollution, historical (old burdens) and current heavy industry in the catchment area, and, of wastewater and urban pollution, respectively.

By considering these indicators and identifying emission sources (e.g., wastewater treatment plants, destructed infrastructure and industry along the main river and its tributaries) and accumulation areas that are relevant for remobilization, statements can be obtained about the high dynamics of the flood event. Furthermore, the importance of natural floodplains for the accumulation and remobilization of organic pollutants, but also the self-purification of water bodies is thus investigated and emphasized. This is of great importance for the holistic assessment of the fate and behaviour of organic pollutants as well as for the estimation of short- and long-term environmental risks and hazards related to (extreme) flood events.

How to cite: Schwanen, C., Bellanova, P., and Schwarzbauer, J.: The 2021 Flood Disaster in Germany – Distribution, remobilization and accumulation of organic pollutants along the natural floodplains of the Rur river, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12558, https://doi.org/10.5194/egusphere-egu22-12558, 2022.

14:32–14:38
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EGU22-8550
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ECS
Piero Bellanova, Jan Schwarzbauer, and Klaus Reicherter

The 2021 European floods (July 13th–16th, 2021) marked Germany’s deadliest (>180 fatalities) and most costly (>€ 30 billion) natural disaster of the 21st century. In North Rhine-Westphalia (Germany) the floods have caused drastic scenes of destruction along small mountainous river systems, such as the Vicht and Inde rivers. Alongside this destruction stands the release of organic pollutants and the remobilization of sediment-associated old burdens in the former mining area of Stolberg. In a preliminary study 10 samples along the floodplains and urban areas of Vicht and the successive Inde rivers have been collected directly after the flood to determine the pollution concentration, dispersion and potential sources. With this information an assessment of the short-term and long-term environmental risks can be evaluated.

First results show acute enrichment of organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs – petrogenic pollutants), polychlorinated biphenlys (PCBs – old burdens/plasticizers) and linear alkylbenzenes (LABs – sewage). The sewage indicators show their highest release and accumulation in samples taken in the urban areas, and subsequently dilute along the natural floodplain segments. This repeats for at least for Stolberg and Eschweiler, which were flooded by the Vicht and Inde, respectively. Old burdens, such as represented by PCBs, related to historical and present heavy industry in the vicinity to the rivers. The flood caused the remobilization of respective old burdens from contaminated plains and urban sources. Petrogenic markers, especially those of PAHs, have been measured in concentrations of mg/kg, vastly exceeding all environmental guidelines and restrictions. These can also be linked to the flooding of industrial and urban sites (e.g., household oil heating tanks, vehicles).

The wide range of observed pollution and fast dispersion of sediment-associated pollutants can be linked to the highly dynamic nature of this flood. In addition, the multitude of historical (mining, heavy industry) and present sources (e.g., fuels, oil, factory effluents, wastewater), sediment-associated pollutants have been remobilized or acutely released with the flood. This unprecedented 2021 European floods may allow insights into the relationships and interactions between hydrodynamics, sedimentology and pollution during such events.

How to cite: Bellanova, P., Schwarzbauer, J., and Reicherter, K.: Toxic European Summer Flood – Dispersion of organic pollutants along the Vicht and Inde rivers, Germany, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8550, https://doi.org/10.5194/egusphere-egu22-8550, 2022.

14:38–14:44
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EGU22-6925
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ECS
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On-site presentation
Clarissa Glaser, Michelle Engelhardt, Beate Escher, Andrea Gärtner, Martin Krauss, Maria König, Rita Schlichting, Christiane Zarfl, and Stephanie Spahr

Storm events lead to a mobilization of dissolved and particle-associated organic pollutants that pose a risk to river ecosystems. Target screening can hardly capture the broad range of compounds present in stormwater and receiving streams. Thus, an additional monitoring proxy that describes the overall chemical load in stormwater is needed. Each chemical in a mixture contributes, albeit with different potency, to cytotoxicity measured by reduction of cell viability after 24h in four human cell lines. Thus, the aim of this study was to investigate the applicability of cytotoxicity as a proxy for the organic contaminant load of rivers during storm events. Field investigations took place in the Ammer River (annual average discharge 0.87 m³ s-1) close to Tübingen, Germany, during intense precipitation events in June 2021. The sampling site was located at the outlet of the gauged catchment (134 km²), thus, integrating inflowing water from all upstream tributaries and sewer overflows. During storm events, high-resolution temporal monitoring of discharge, suspended particles, particle characteristics, as well as dissolved and particle-associated organic contaminants was conducted using both chemical analyses and cell-based in vitro bioassays. The cytotoxicity in the water phase (expressed as toxic units, TU), was similar among the cell lines. The TU flux followed the course of the hydrograph with highest values at the maximum or slightly after the discharge peak. This finding suggests that the chemical load is controlled by the transported volume of water despite the fact that different contaminant sources are likely to contribute to the water flux and pollutant load in the river at different time points of the hydrograph. For the particle-associated cytotoxicity, the TU flux also followed the course of the events suggesting that the particle-associated cytotoxicity in the river is, similar to the water cytotoxicity, controlled by the particle load in the river. This highlights that the cytotoxicity is a suitable proxy to detect mixtures of organic compounds and, thus, assess the chemical load in rivers during storm events.

How to cite: Glaser, C., Engelhardt, M., Escher, B., Gärtner, A., Krauss, M., König, M., Schlichting, R., Zarfl, C., and Spahr, S.: Cytotoxicity as a proxy for particle-associated and dissolved organic contaminant loads in rivers during floods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6925, https://doi.org/10.5194/egusphere-egu22-6925, 2022.

14:44–14:50