UP3.1

This study investigates whether the recent extremely hot and dry summers (2003, 2015, 2018 and 2019) in Germany will be normal summers under future climate change conditions from climate projections. Abnormally persistent high-pressure systems during these recent German summers maintained clear skies and dry conditions on the ground, resulting in record-breaking heat and drought conditions which had major socio-economic impacts, e.g. reduced crop yields or impacts on human health and increased mortality. Heat and drought indices are calculated from the German Meteorological Service's (DWD) climate model reference-ensembles for periods 2031-2060 and 2071-2100 under greenhouse gas emission scenarios RCP 2.6 (11 ensemble members) and RCP 8.5 (21 ensemble members). These results are compared with the same indicators calculated from three observational datasets (station data and gridded datasets: HYRAS and DWD Climate Monitoring Grids). The order of recent extreme summers in Germany from hottest and driest is: 2018, 2003, 2019, 2015. The climate projections show increasing summer heat conditions for Germany throughout this century, especially for the RCP 8.5 scenario, but no clear future summer precipitation anomaly trend. These recent extreme summers would be considered extremely hot summers for RCP 2.6 in 2031-2060, 2071-2100 and the RCP 8.5 2031-2060 scenarios, but would be considered normal or even below normal hot summers under the RCP 8.5 scenario in 2071-2100. Due to the combination of extreme heat and strong precipitation deficits, the climatic water balance and derived meteorological drought indicator values of these summers often exceeds the considered likely ranges projected for all future summer scenarios and are only matched by the most anomalous hot and dry summers in the model ensembles, even for the high-emission RCP 8.5 scenario in 2071-2100.

How to cite: Stanley, K., Leps, N., and Walter, A.: Recent hot and dry summers in Germany in comparison to climate projections, EMS Annual Meeting 2022, Bonn, Germany, 5–9 Sep 2022, EMS2022-24, https://doi.org/10.5194/ems2022-24, 2022.

Observed changes in the seasonal and annual air temperature and precipitation amounts, and the corresponding indices of extremes in Croatia are analysed. Daily data from the 1961-2020 period are employed at 37 climatological stations (mean and extreme air temperatures) and 164 rain gauge stations (precipitation amounts) operated by the Croatian Meteorological and Hydrological Service. The trends are estimated using linear regression and the statistical significance of trends is tested by the Mann-Kendall test. The results revealed a consistent warming trend in the whole country. The highest increase in the mean annual air temperature (up to 0.5 °C/10years) is detected in central continental Croatia mostly due to summer and winter positive trends. Observed warming is also evident in positive trends of warm temperature indices (warm days, warm nights and warm spells) and negative trends in cold temperature indices (cold days, cold nights and cold spells). A significant decrease in the summer precipitation amounts is found along the Adriatic coast and in the highlands (5-15 %/10years), in the latter region also in spring. The most prominent feature of precipitation changes is a consistent positive trend in autumn rainfall amounts across the whole country, with the largest increase detected in central parts. The observed trends are associated with an annual increase in dry spell (DS) lengths in the central parts and along the Adriatic coast, and with a significant decrease in DSs in easternmost Croatia. Moreover, in the central, mountainous and northern Adriatic region, a significant increase in precipitation fraction due to very wet days (R95T) and in daily intensity index (SDII) is found. The summer drying is associated with a decrease in the number of moderately wet days along the Adriatic and the highlands but also with an increased number of dry days and DS lengths, and a decrease in the SDII and highest 1-day (Rx1d) and 5- day (Rx5d) precipitation amounts. On the other hand, autumn wetter conditions are mainly associated with an increase in R95T and with shorter DS lengths but also with an increase in SDII and Rx1d and Rx5d. The spring trend pattern is characterised by longer DS lengths in the northern Adriatic and longer wet spells in eastern Croatia.

How to cite: Cindric Kalin, K., Patalen, L., Marinovic, I., and Pasaric, Z.: Trends in temperature and precipitation indices in Croatia, 1961-2020, EMS Annual Meeting 2022, Bonn, Germany, 5–9 Sep 2022, EMS2022-212, https://doi.org/10.5194/ems2022-212, 2022.

National hail climatology of Croatia

Lucija Blašković, Damjan Jelić, Barbara Malečić, Branimir Omazić, Maja Telišman Prtenjak (1)

(1) University of Zagreb, Faculty of Science, Department of Geophysics, Zagreb, Croatia

The step every country should take towards a better understanding of hail is national climatology. It is crucial to explore the temporal and spatial characteristics of this small-scale phenomenon in hope that it will contribute to better defense and preparation for such extreme weather. Even though Croatia is a small country, it has a relatively inhomogeneous climate due to its proximity to the Adriatic sea, a mountain range that in a way separates Croatia, etc. This research will analyze the diversity of the Croatian climate and its impact on the occurrence of hail. The results are based on hail data from 186 stations. This digitized data vary from station to station, so different time periods were observed. The results showed significant interannual and spatial variability, due to which it was necessary to divide into subdomains based on the season in which hail predominates - on the entire coast, the highest hail activity is present in the colder part of the year while the continental part of Croatia shows increased summer hail activity. There is also a transitional area that records most hail in spring and fall. The trend analysis was made for two time periods: 1.) from 1964. to 2019., 2) from 1984. to 2019. and both periods have shown signs of a negative trend in a number of hail events. Daily patterns show a shift in the daily maximum from morning to afternoon hours as we approach the continent from the coast, and the highest frequencies are recorded in Šibenik and Zavižan of as much as 3.8 and 4.8 days with hail per year. Finally, instability indices were studied, which could explain the atmospheric conditions in which hail occurs.

How to cite: Blašković, L., Jelić, D., Malečić, B., Omazić, B., and Telišman Prtenjak, M.: National hail climatology of Croatia, EMS Annual Meeting 2022, Bonn, Germany, 5–9 Sep 2022, EMS2022-349, https://doi.org/10.5194/ems2022-349, 2022.

The Clausius-Clapeyron (CC) equation describes the change in saturated water vapor pressure with temperature (7% per degree C within the normal temperature range). The possible effects of deviations from CC scaling, especially the so-called "super CC" scaling (increase above 7%), on the occurrence and intensity of precipitation extremes are connected to many different factors. The most important of them are the availability of moisture and more intense convection. The resulting CC scaling is influenced also by the type of precipitation and the super CC scaling may be the result/artifact coming from combination of precipitation of different types. Here, we present a study of the variability in the rates of increase in precipitation intensity with dew point temperature using the Multi Source Weighted Ensemble Precipitation (MSWEP) 3h data with the resolution of 0.1 deg. for 2006–2016 over Central Europe. The scaling is assessed for daily dew point temperature (taken from ERA5-Land dataset) and the 95th percentile of 3h precipitation using the quantile regression method. As the resulting scaling may be influenced by the type of precipitation (convective versus non-convective), we apply the method of threshold precipitation rate (THR) to categorize the precipitation in two subsets. The average scaling slopes are 8.7 %/°C for all precipitation events, 6.8 %/°C for precipitation events above THR and 3.0 %/°C for events bellow THR. The mixing of events bellow/above THR amplifies the scaling. To evaluate the scaling of convective precipitation with dew point temperature independently, we use the data of lightning occurrence from the EUCLID dataset (3h, resolution 0.1 deg.), as the lightning occurrence is assumed to be a robust proxy for convective precipitation. The average scaling slopes are 13.4 %/°C for precipitation events with lightning and 6.3 %/°C for precipitation events without lightning. The scaling of the events with lightning corresponds with the double CC scaling for convective events reported by previous studies.

How to cite: Martinkova, M. and Kysely, J.: Precipitation-Temperature Scaling of 3h Convective Precipitation over Europe, EMS Annual Meeting 2022, Bonn, Germany, 5–9 Sep 2022, EMS2022-88, https://doi.org/10.5194/ems2022-88, 2022.

The study aims to estimate the future climate change of extreme precipitation over the topographically complex coastal-mountainous region of the eastern Adriatic and Dinaric Alps, which is particularly vulnerable to climate change. A number of studies classify this region as an area with a "zero-change" line between the wetter north and drier south, which shifts northward towards the end of the century. However, the research on future extreme precipitation changes over this region is still limited. We use an unprecedented ensemble of ~140 regional climate model (RCM) simulations of future climate from the EURO-CORDEX ensemble at 0.11° resolution, to cover as many future conditions and sources of uncertainty as possible. The ensemble is comprised of 15 RCMs driven by 11 CMIP5 global climate models. The climate change signal is estimated for three different greenhouse gases concentration scenarios (RCP2.6, RCP4.5 and RCP8.5) and several future periods (2041-2070, 2071-2100) with respect to the historical period (1971-2000). We focused on heavy precipitation measures: the 99th percentile of all-day precipitation, number of heavy and very heavy precipitation days, maximum one-day and five-day aggregated precipitation sum. Additionally, we have applied the extreme value analysis, specifically the generalized extreme value theory, to assess extreme precipitation return levels associated with return periods between 10 and 100 years. The results are highly dependent on period, scenario, season and location. Overall, results show an intensification of both heavy and extreme precipitation events, especially during cold seasons over the north-eastern areas for the far future period. For this projected change, models show high agreement as opposed to that in summer, when most of the examined indices display the aforementioned south-north gradient. A more detailed analysis is planned to quantify the climate change signal for several subdomains of interest.

How to cite: Ivušić, S., Güttler, I., and Horvath, K.: Projected extreme precipitation changes over the coastal-mountainous region of the eastern Adriatic and Dinaric Alps, EMS Annual Meeting 2022, Bonn, Germany, 5–9 Sep 2022, EMS2022-446, https://doi.org/10.5194/ems2022-446, 2022.

While anthropogenic global warming is well-accepted and thoroughly described in the climate community, the vast majority of the general public is still not always fully-certain whether to associate specific local weather or climate event with this global phenomenon. It is of utmost importance to raise public awareness by providing easily understood but scientifically sound information, and to explain how the anthropogenic activity contributes to specific weather or climate events. Although it is getting to be widely assessed now in Western Europe, only a few case studies for past high-impact local weather events were assessed in Hungary, and the systematic analyses of long-term trends of such indicators with their linkage to anthropogenic activity are missing in this region. Our local attribution project (started in September 2021) aims to fill this gap in Hungary: the results of the analyses of seasonally relevant indices are published in each season at around a time of an event occurrence or absence. Dissemination is executed via an already established, online Hungarian platform (https://masfelfok.hu/, meaning “1.5 degrees”), since it is reaching the general public with its readily understood climate change information through its broad media coverage and a growing social media network.

The analysis uses several freely-available data sets: (1) an ensemble selection of CMIP6 global climate model simulations with both natural-only forcings and historical runs, (2) a fit-for-purpose ensemble of regional climate model simulations from the Euro-CORDEX on 0.11° resolution, including the RCP2.6, RCP4.5 and RCP8.5 future scenarios, (3) a fine-resolution, homogenized observation-based gridded data for Hungary, compiled by the Hungarian Meteorological Service, (4) the newest E-OBS database for the area outside of Hungary. Within the project, we selected seasonally relevant extreme, less extreme but well-known events, and these pre-selected indices are attributed to anthropogenic activity through their detected intensity, duration, or frequency changes. For instance, third-level heatwave days, hot days, tropical nights, annual temperature maxima and return values, meteorological droughts, and heavy precipitation days are evaluated for summer, as they have the largest public interest and impacts in our target region.

How to cite: Szabó, P., Bartholy, J., and Pongrácz, R.: Attribution of pre-selected climate indicators in summer over the Carpathian basin, EMS Annual Meeting 2022, Bonn, Germany, 5–9 Sep 2022, EMS2022-450, https://doi.org/10.5194/ems2022-450, 2022.

Every year, extreme wind events cause a great deal of financial losses across Europe. As such, the accurate projection of the changes in extreme winds will be invaluable for many industries, including insurance, construction, energy, and afforestation. Adaptation planning requires the estimation of how the magnitude and frequency of extreme events, such as extreme winds, will vary in the future.

Extreme winds are examined in a selection of Euro-CORDEX downscalings. Since these include multiple downscalings of the same global climate models by different regional climate models, it is possible to intercompare how different models represent extreme winds. The peaks-over-threshold approach is used identify the extreme events based on the fitted Generalized Pareto Distributions (GPD), and maps of 30-year return winds for all locations over Europe are presented. Future changes in the frequency of extreme winds are assessed for Northern, Central, and Sothern Europe for three future periods, being the near, mid, and end of this century. The results show that the frequency of extreme wind events will increase from one period to the next over the 21^st century in all three regions of Europe.

The results of the recently published study will be presented in detail along with a brief overview of the statistical methods employed. Our ongoing work to create a comprehensive dataset of assessed extreme winds and precipitation will also be addressed. Time permitting, we will present evidence of the benefits of downscaling, an assessment of how the base period length affects the uncertainties, and a brief comparison of the different methods commonly employed to assess uncertainties.

How to cite: Outten, S. and Sobolowski, S.: Assessment of extreme winds over Europe in Regional Climate Models, EMS Annual Meeting 2022, Bonn, Germany, 5–9 Sep 2022, EMS2022-365, https://doi.org/10.5194/ems2022-365, 2022.

The regional impacts of anthropogenic climate change over Europe are still very unclear, in large part due to uncertainties in the dynamical response of the large-scale circulation. Particularly in Boreal winter, the structure of the Euro-Atlantic circulation is strongly nonlinear, and is dominated by Rossby wave breaking, persistent atmospheric blocks and latitudinal meandering of the eddy driven jet stream. In the face of this complexity, adopting a regime approach – where the large scale circulation is decomposed into a small number of representative flow state – can shed much needed light on the internal variability and forced response of Euro-Atlantic dynamics.

One major open question is how exactly nonlinear regimes respond to a warming climate. While it has been hypothesised that climate forcing should primarily result in a shift in the probability of historically observed regimes, rather than inducing new flow configurations, this has never been tested in complex earth system models. In this work we fill this gap, by analysing regime statistics in 20 CMIP6 models under the SSP5-8.5 scenario. We decompose the forced response into two components: one representing the degree to which the prevailing regime patterns alter, and another representing their changing probability of occurrence and persistence. We show that while robust changes in regime patterns can be detected, these are minor in comparison to changes in the regime life-cycles. The overall picture tends towards a less regime dominated future: we find that anticyclonic regimes associated with persistent blocking are projected to become less persistent in the future and that central jet positions, associated with zonal flows, become more common. However considerable intermodel variability, even in the sign of the prevailing regime trends, shows the need for further investigation, and an improved representation of Euro-Atlantic regimes in state-of-the-art models.

How to cite: Dorrington, J., Strommen, K., Fabiano, F., and Palmer, T.: How do Euro-Atlantic regimes respond to climate change?, EMS Annual Meeting 2022, Bonn, Germany, 5–9 Sep 2022, EMS2022-266, https://doi.org/10.5194/ems2022-266, 2022.

The Nordic-Baltic region has experienced numerous flooding episodes resulting from heavy rainfall. Such events are costly and may potentially threaten the safety of the population. As part of the cooperation in the Nordic Framework for Climate Services (NFCS), we here present results from two separate analyses of heavy precipitation in a large region covering Fennoscandia and the Baltics (Dyrrdal et al., 2021; Olsson et al., 2022).

In Dyrrdal et al. (2021), long-term (1901–2020) changes of annual maximum daily precipitation from 138 stations and short-term (1969–2020) changes from 724 stations were analyzed, along with their date of occurrence. Results show a majority of positive trends in daily annual maxima and the 5-year return level, with hotspots in southeast Norway, southern Sweden and southwest of Finland. Almost all stations with a statistically significant trend showed an increase in the intensity of annual maximum 1-day precipitation during the last 50 years. In the region as a whole, annual maximum precipitation events occur somewhat later in the year now compared to the beginning the last century

For urban flooding, the occurrence of short-duration rainfall is of special importance. In Olsson et al. (2022), sub-daily rainfall observations from 543 meteorological stations in the Nordic-Baltic region were collected, quality controlled and consistently analyzed in terms of records, return levels, geographical and climatic dependencies, time of occurrence of maxima and trends. The results reflect the highly heterogeneous rainfall climate in the region, with longitudinal and latitudinal gradients as well as local variability, and overall agree with previous national investigations. Trend analyses for Norway and Denmark indicated predominantly positive trends in the period 1980-2018. 

References:

Dyrrdal, A.V., Olsson, J., Médus, E., Arnbjerg-Nielsen, K., Post, P., Aņiskeviča, S., Thorndahl, S., Førland, E., Wern, L, Mačiulytė, V. and Mäkelä, A., 2021: Observed changes in heavy daily precipitation over the Nordic-Baltic region, Journal of Hydrology: Regional Studies, 38, 100965, ISSN 2214-5818, https://doi.org/10.1016/j.ejrh.2021.100965.

Olsson, J., Dyrrdal, A.V., Médus, E., Södling, J., Aniskeviča, S., Arnbjerg-Nielsen, K., Førland, E., Mačiulytė, V., Mäkelä, A., Post, P., Thorndahl, S.L., and L. Wern (2022) Sub-daily rainfall extremes in the Nordic-Baltic region, Hydrol. Res., in press.

How to cite: Dyrrdal, A. V., Olsson, J., Médus, E., Arnbjerg-Nielsen, K., Post, P., Aņiskeviča, S., Thorndahl, S., Førland, E., Wern, L., Mačiulytė, V., Mäkelä, A., and Södling, J.: Observed changes in heavy precipitation over the Nordic-Baltic region, EMS Annual Meeting 2022, Bonn, Germany, 5–9 Sep 2022, EMS2022-368, https://doi.org/10.5194/ems2022-368, 2022.

The Atacama Desert should be a region prone to wind erosion and dust events given the barren landscape and lack of moisture but it rarely sees strong dust events. Despite this perception, there is no literature quantifying the frequency of dust events in the Atacama and analysing the underlying meteorological mechanisms responsible for dust storms in the region. To this end, we analysed surface observations spanning 37 years (1984-2021) to compile wind climatology and systematically assess the dust events in the Atacama Desert. We used the Met Office Integrated Data Archive System (MIDAS) Land and Marine Surface Stations Data. Based on the present weather codes for nine Chilean stations present in the data, frequency of dust events was computed. The Atacama Desert has a very low annual mean dust event frequency of 0.6% despite its hyper-aridity. The station at Chañaral records the highest number of dust events, accounting for 68% of all recorded dust observations. There is no perceptible seasonal pattern but there is a strong diurnal cycle in the dust activity in the Atacama as most dust events occur between 1500 and 1800 local time. Threshold wind speeds, defined as the minimum wind speed required for 5, 25 and 50% of dust event frequency, are estimated for all stations except at Vallenar. The thresholds allow us to determine the lowest winds capable of emitting dust from the surface and also the highest wind speeds required, and the differences between the thresholds is indicative of the changes in soil conditions such as soil moisture or land use. For 5% of dust event frequency, the lowest threshold wind speed of 6-8 ms^-1is estimated at Chañaral and for 50% of dust event frequency, 10-12 ms^-1at Desierto de Atacama. Higher threshold wind speeds are observed for stations north of 26°S than the stations south of 26°S. It implies that dust particles can be mobilized by weaker near-surface wind speeds in the South than in the North of the Atacama. Seasonal variations in the threshold wind speed are not strongly pronounced in stations where sufficiently many observations are available. Ongoing work includes incorporating additional datasets for filling in identified data gaps in MIDAS and for allowing a spatially broader analysis of dust-emitting winds across the Atacama Desert.

How to cite: Pinto, R. and Fiedler, S.: Dust Event Assessment for the Atacama Desert using Surface Synoptic Observations: 1984 - 2021, EMS Annual Meeting 2022, Bonn, Germany, 5–9 Sep 2022, EMS2022-90, https://doi.org/10.5194/ems2022-90, 2022.

With increasing air temperature in a warming climate the soil temperature also increases. Such changes impact flora, fauna and natural hazards. Thus, it is important to monitor soil temperature. In Iceland, the highland station Hveravellir has the longest reliable time series of soil temperature. The station is located in a barren landscape at 641 m a.s.l., but the site itself is grass covered. Soil temperature has been measured there since 1965 at 10, 20, 50 and 100 cm depth but the data is not fully digitized. Here, the time series used span 42 years, from 1977 to 2019. Annual and seasonal trends are calculated as well as the annual number of thawing degree days (TDD) and freezing degree days (FDD). During this period, there has been a considerable warming in Iceland, not only because of global warming but also because of its start coinciding with the end of a local cold period. In the soil, warming is detected in all seasons except May to June, which is the melting season, the end of which varies greatly from year to year. The most warming is found during the autumn and winter months. These results contrast with those from continental cool sites where the largest warming has been seen in the spring months. The autumn cooling starts 2–3 weeks later now than at the start of the time series, resulting in a longer summer in the soil. The number of TDD has increased and the number of FDD has decreased, both in air and in soil. At 100 cm depth TDD has increased by 80°C day dec ⁻¹ and FDD decreased by 38°C day dec ⁻¹. There is a correlation between the increase in air temperature and soil temperature, for every 1°C increase in 2 m temperature the soil temperature at 100 cm has increased by 0.6°C. The implication of this warming is firstly seen in terms of flora, fauna and agriculture, by the lengthening of the growing season, and secondly in terms of natural hazard, by increased risk of landslides due to thawing of permafrost in montainous regions.

How to cite: Petersen, G. N.: The soil warming in the Icelandic highlands, EMS Annual Meeting 2022, Bonn, Germany, 5–9 Sep 2022, EMS2022-588, https://doi.org/10.5194/ems2022-588, 2022.