Orals: Fri, 2 May | Room 0.14
In mid-latitude regions, the development of a heatwave is closely linked to a quasi-stationary anticyclonic flow anomaly. For many cases over Europe, these anomalies are associated with atmospheric blocking events, which in summer usually manifest themselves in form of a so-called Omega blocking. However, not all heatwaves necessitate atmospheric blocking. Indeed, some heatwaves are enabled by poleward extensions of the subtropical high pressure belt, forming an atmospheric ridge pattern. We hypothesize that both the origin of the involved air masses as well as the processes modulating the air mass along its path to Central Europe may differ fundamentally between heatwaves forming under an Omega blocking and those that are initiated by a subtropical ridge.
In this work, we therefore select the respective 20 most textbook-like cases of Omega and ridge-type Central European heatwaves in the period of 1950 to 2023. Based on high-resolution ERA5 data, we conduct a Lagrangian analysis into the properties of air masses and the relative importance of the three processes warming the involved air masses, namely advection, adiabatic warming by subsidence and diabatic warming through sensible heat fluxes. By computing a large number of backward trajectories using Lagranto and the subsequent application of a Lagrangian temperature decomposition algorithm, we quantify the relative importance of each of the three mentioned processes. This analysis is done separately for the onset day and the subsequent three days of the heatwave.
Omega- and ridge-type heatwaves feature some significant differences in both air mass origin and the relative importance of the processes leading to anomalously high near-surface temperatures, which tend to become more apparent in the more mature stage of the respective type of heatwave. Overall, ridge-type heatwaves tend to be characterized by a higher advective contribution to the overall temperature anomaly. This is directly related to the fact, that the involved air masses tend to originate from slightly more southern and climatologically warmer regions. Particularly two or three days after heatwave onset, anomalous subsidence and associated adiabatic heating contributes significantly more to warming in ridge-type than in omega-type heatwaves. In turn, omega-type heatwaves are characterized by a significantly stronger contribution of diabatic heating. This is mostly due to air masses spending more time in the planetary boundary layer and stronger short-wave radiation along the air masses' path.
How to cite: Lemburg, A., Fink, A. H., and Pinto, J. G.: Lagrangian analysis of two flavours of Central European heatwaves: development under Omega blocking vs. initiation by subtropical ridges, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11816, https://doi.org/10.5194/egusphere-egu25-11816, 2025.
Heatwaves (HWs) are extremely harmful weather phenomena that cause significant damage to the environment and society. Numerous studies have shown a substantial increase in the frequency and intensity of HWs in various parts of the world. Therefore, investigating the meteorological factors contributing to HW formation is an important task. In this study, we investigated the main air transport patterns associated with the most severe HWs observed during 1940-2023 in Spain and Ukraine.
Firstly, based on ERA5 (2 m) air temperature data, we identified all HW events for each grid point in both countries with the heatwaveR package. Following the approach used in many studies, a HW was defined as an extreme weather phenomenon when daily maximum air temperature exceeds 90-th percentile at least for three consecutive days. Additionally, each detected HW episode was categorized as moderate, strong, severe, or extreme based on its maximum observed intensity. A final list of HWs for further analysis in each country was compiled by selecting events with a spatial extent covering more than 20% of the country’s territory and with severe or extreme category identified in at least one grid point. Using this methodology, we selected 80 HW episodes in Spain and 18 in Ukraine.
Backward trajectories for the selected HW episodes were calculated using the HYSPLIT model, with ERA5 3D-data serving as input meteorology. For each HW event, only first three days were considered, regardless of the event's total duration. A starting location for backward trajectories for each HW was defined as a midpoint of its spatial extent. Additionally, to assess the influence of vertical wind shear on trajectory calculations, three altitudes (10, 1500, and 5000 m AGL) were defined as the starting heights. Backward trajectories were initiated hourly over the 3-day period and calculated for the seven days preceding each release hour. In total, 216 backward trajectories were calculated for each HW episode (72 trajectories per release height). The calculated trajectories were then grouped into three clusters based on the HYSPLIT clustering approach and a mean trajectory was determined for each cluster. Along with the cluster analysis, we also identified the dominant circulation types and their evolution during the selected HW episodes. This analysis was performed using the synoptReg package based on ERA5 mean sea level pressure data.
The mean cluster trajectories, calculated for all selected HWs, were used to build trajectory frequency maps, showing the most preferential routes of air masses associated with the severe and extreme HWs. Analysis of these maps revealed that a westerly trajectory flow is the most likely route for air masses responsible for the most intense HWs in Spain and Ukraine. In Spain, air masses are typically transported from the Atlantic, whereas in Ukraine, they traverse across Western Europe. Other directions of air mass transport, including from the south, occur relatively rarely. Our findings align with other similar studies for other regions in Europe, which suggest that heat advection is not dominant mechanism for HW formation.
This work has received funding through the MSCA4Ukraine project, funded by the European Union
How to cite: Skrynyk, O., Aguilar, E., Skrynyk, O., and Cimolai, C.: Cluster analysis of HYSPLIT backward trajectories for major heatwaves in Spain and Ukraine (1940–2023), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8195, https://doi.org/10.5194/egusphere-egu25-8195, 2025.
Pronounced spatial disparities in heatwave trends are bound up with a diversity of atmospheric signals with complex variations, including different phases and wavenumbers. However, assessing their relationships quantitatively remains a challenging problem. Here, we use a network-searching approach to identify the strengths of heatwave-related atmospheric teleconnections (AT) with ERA5 reanalysis data. This way, we quantify the close links between heatwave intensity and AT in the Northern Hemisphere. Approximately half of the interannual variability of heatwaves is explained and nearly 80% of the zonally asymmetric trend signs are estimated correctly by the AT changes in the mid-latitudes. We also uncover that the likelihood of extremely hot summers has increased sharply by a factor of 4.5 after 2000 over areas with enhanced AT, but remained almost unchanged over the areas with attenuated AT. Furthermore, reproducing eastern European heatwave trends among various models of the Coupled Model Intercomparison Project Phase 6 largely depends on the simulated Eurasian AT changes, highlighting the potentially significant impact of AT shifts on the simulation and projection of heatwaves.
How to cite: Cai, F., Liu, C., Gerten, D., Yang, S., Zhang, T., Li, K., and Kurths, J.: Sketching the spatial disparities in heatwave trends by changing atmospheric teleconnections in the Northern Hemisphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7402, https://doi.org/10.5194/egusphere-egu25-7402, 2025.
Due to global warming, climate extremes like heatwave events will rise further in the 21st century. Earlier, heatwave characteristics like duration, intensity, and frequency have been studied independently, ignoring interdependence among them, leading to biases in the heatwave impact assessment. The heatwave intensity duration frequency(HIDF) model provides a feasible framework incorporating interdependencies among heatwave characteristics, helping quantify heatwave hazards more accurately. HIDF curves are produced for six metropolitan cities, namely, Ahmedabad, Bhopal, and Gwalior over the western part and Patna, Varanasi, and Deoghar over the eastern part of northern India using the Indian Meteorological Department daily maximum temperature from 1961-2023 for March-June months. Heatwave events of durations ranging from one to ten and their respective intensities are modeled using the nonparametric kernel distribution method. HIDF curves reveal that the intensity and frequency of heatwave events for each duration increased(decreased) in the western(eastern) cities. In Ahmedabad city, the likelihood of a six-day heatwave event increased by 59 %, whereas it decreased by 66 % over Patna, reflecting east-west asymmetry. We found that a positive anomaly pattern over the southern Atlantic Ocean, i.e., Atlantic Nino, influences heatwaves occurring over northern India, causing east-west asymmetry. Due to the Atlantic Nino, the cross-equatorial flow reversed its direction as the moisture from the northern Indian Ocean, instead of traveling towards north China, entered the eastern part of India. This resulted in entry of moisture laden winds from the Bay of Bengal and it contributed to more convection activity in northeast India causing temperature drop in the region. The strength of moisture-laden winds is reduced when they reach the western part; the chance of convection decreases, contributing to a rise in temperature. Our results provide significant inputs in understanding heatwave dynamics over northern India, which will be helpful in predicting the heatwaves more accurately in the future.
How to cite: Dalal, G., Hari, V., and Chaudhary, S.: Asymmetric response of Atlantic Nino on heatwaves over Northern India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-592, https://doi.org/10.5194/egusphere-egu25-592, 2025.
Rising temperatures driven by climate change pose significant challenges worldwide. In Brazil, these challenges include extreme weather events such as heatwaves, which can have severe health impacts. This study investigates the influence of atmospheric blocking events and episodes of the South Atlantic Convergence Zone (SACZ) on Brazil's occurrence and intensity of extreme heatwaves. Atmospheric blocking and SACZ episodes were characterized using indices developed at LAMMOC/UFF, which effectively capture the behavior of these systems across different regions of the country. Atmospheric blocking events are typically associated with prolonged droughts, while SACZ episodes are linked to intense, spatially well-distributed precipitation. The newly developed Extreme Heatwave (XHW) index was applied in this study due to its global applicability, covering all 26 state capitals and the Federal District of Brazil. The SACZ index was calculated using NCEP Reanalysis data (I and II) while blocking and XHW indices were calculated using ERA5 reanalysis data, generating a time series from 1960 to 2024. To facilitate statistical analyses, all data were normalized. Methods such as Pearson’s correlation coefficient, Principal Component Analysis (PCA), K-means clustering, trend analysis, and the Mann-Kendall test were applied to identify and quantify trends in the series. The results showed an increase in extreme heat events in most cities, except for Florianópolis (in the South) and Fortaleza (in the Northeast), which displayed no significant trend. Atmospheric blockings also showed a clearer upward trend across all evaluated regions compared to SACZ episodes. The correlation between the SACZ and heatwaves is statistically insignificant across most of Brazil, with values close to zero, as the SACZ is not associated with significant temperature gradients, causing little to no impact on the occurrence of heatwaves. In contrast, atmospheric blockings show statistically significant positive correlations with heatwaves, particularly in geographically specific regions. For example, in the North region, Palmas (TO) stands out with a correlation of 0.44, while Manaus (AM) approaches a value of 0.38. These cities are more responsive to northern-located blockings. Rio de Janeiro (RJ), in the Southeast, and Cuiabá (MT), in the Central-West, exhibit a correlation of 0.37 due to southern and northern-located blockings, respectively. In the South, Porto Alegre (RS) is the most responsive to southern-located blockings with a correlation of 0.18. In the Northeast, values are generally low, with Recife (PE) showing the highest correlation (0.16) for northern-located blockings. This study emphasizes the importance of spatial analysis in understanding the influence of atmospheric blockings on extreme heatwaves events, revealing a direct relationship between the position of blockings and their impact, as evidenced by the varying responses of different cities. As atmospheric blockings increase in frequency due to climate change, heatwaves are also expected to become more frequent and intense. This trend poses a growing risk to public health and mortality, as well as significant challenges to the healthcare system.
How to cite: da Fonseca Aguiar, L., Galves, V. L., Esposte Coutinho, P., Sancho, L., and Cataldi, M.: Influence of Atmospheric Blocking and SACZ Episodes on Extreme Heatwaves in Brazil: A Long-Term Analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11431, https://doi.org/10.5194/egusphere-egu25-11431, 2025.
In July 2023, a series of heat extremes hit the North Hemisphere, which posed threats to the high-risk population and societal infrastructure in Eastern Canada, the Mediterranean, and Central Asia. Here we identify a dynamical linkage behind the spatiotemporal compounding nature of heatwaves over the three regions. However, it remains unclear whether these record-shattering extremes were amplified by specific recurrent atmospheric teleconnection patterns. By investigating the 2023 case and conducting historical analysis, we show that the Northern Hemispheric concurrent heatwaves in July 2023 were attributed to a recurrent wave-6 pattern. In particular, pre-existing warmth and drought over Eastern Canada in early-July intensified the wave-6 teleconnection; which then led to extreme heatwaves over the Mediterranean and Central Asia in mid-July 2023. Furthermore, we reveal that the wave train was generated by early-July convection over the northern subtropical Pacific together with the lowest May snow cover over North America in the past 40 years helped to warm Eastern Canada. Multiple models from the Coupled Model Intercomparison Project 6 can also simulate those compound extremes connected by the wave-6 pattern with a high inter-model agreement. Our research offers insights into record-breaking compounding heatwaves in disparate parts of world during the mid-summer of 2023, with implications for disaster decision-making and risk management.
How to cite: Liu, C., Galfi, V. M., Cai, F., Robinson, W. A., and Coumou, D.: The role of Rossby wave dynamics in spatially compounding heatwaves in mid-summer 2023, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6883, https://doi.org/10.5194/egusphere-egu25-6883, 2025.
We examine near-simultaneous occurrences of cold extremes in North America and wind extremes in Europe, referred to as pan-Atlantic compound extremes. Previous studies have established a robust spatial and temporal relationship between the location of cold extremes and the footprint of wind extremes. Individually, cold and wind extremes are highly impactful, but their coincident occurrence amplifies effects and exposes international actors to correlated losses. This study analyzes the large-scale circulations responsible for pan-Atlantic compound extremes through the lens of weather regimes and Fourier decomposition.
Five distinct dynamical pathways are identified, which non-uniformly govern the occurrence of cold extremes across three regions of North America. Three of these pathways also engender European wind extremes, providing a mechanistic explanation for the observed spatial and temporal relationships of pan-Atlantic extremes. The pathways are as follows:
(i) A persistent Atlantic low producing cold spells in eastern Canada and wind extremes in the British Isles.
(ii) A wave train generating cold spells in the eastern United States, culminating in an Atlantic low and wind extremes in Iberia and the British Isles.
(iii) A wave train producing cold spells in eastern Canada, culminating in Scandinavian blocking.
(iv) A quasi-stationary wave-2 pattern driving cold spells in central Canada and Scandinavian blocking.
(v) An Arctic high generating cold spells in the eastern United States and wind extremes in Iberia.
How to cite: Leeding, R. and Messori, G.: Pathways to concurrent North American cold and European wind extremes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10994, https://doi.org/10.5194/egusphere-egu25-10994, 2025.
We show that the wintertime (December-January-February) North Pacific jet in ERA5 has shifted northwards over the satellite-era (1979-2023) at a faster rate than any of the state-of-the-art CMIP6 coupled climate models used in this study. Differences in tropical sea surface temperature (SST) trends can only partially explain the discrepancy in jet trends between models and observations and a small minority of simulations forced with observed SSTs match the magnitude of the observed jet trend. However, analysis of longer-term jet variability in reanalysis suggests that the jet trend has not clearly emerged from multi-decadal internal climate variability. Consequently, it is unclear whether the difference in observed and modelled jet trends arises due to differing responses to anthropogenic forcing or overly weak long-term internal variability in models. These results have important implications for future climate projections for North America and motivate further research into the underlying causes of long-term jet trends.
How to cite: Patterson, M. and O'Reilly, C.: Climate models struggle to simulate observed North Pacific jet trends, even accounting for tropical Pacific sea surface temperature trends, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19419, https://doi.org/10.5194/egusphere-egu25-19419, 2025.
It is known that some extreme weather events are associated with the appearance of large-scale blocking patterns (e.g. heatwaves and droughts), while others are linked to cut-off low systems that often occur on the southern flanks of the blocking patterns (e.g. extreme precipitation, intense snow storms). These quasi-stationary high-pressure systems disrupt the atmospheric flow, producing significant extreme weather and influencing surface impacts. However, identifying and tracking atmospheric blocks is challenging due to their diverse dynamics.
BLOCS (Blocking Location and Obstruction Cataloguing System) is an open-source, Python-based framework designed to systematically identify, classify, and track atmospheric blocking events. It is based on the state-of-the-art geopotential height gradient methodology (e.g., Sousa et al., 2021) and provides a robust tool applicable to different regular-grid datasets, such as NCEP-NCAR and ERA5. The method captures blocking subtypes (e.g., ridge, omega, Rex) and their life cycles, enabling detailed analyses of their spatial and temporal variability. By integrating customizable parameters, BLOCS can be adapted for studying atmospheric blocking and subtropical ridges under changing climate conditions across diverse datasets (e.g. Coupled Model Intercomparison Project, CMIP; Paleoclimate Modelling Intercomparison Project, PMIP).
Outputs from BLOCS include daily- and event-based catalogues, facilitating the study of blocking dynamics and their influence on extreme weather conditions, such as temperature anomalies and precipitation extremes. BLOCS has been used to analyze historic events like the 2003 European heatwave and the 2010 Russian mega-heatwave, demonstrating its ability to connect blocking patterns to surface impacts. Its applications extend to regional and global studies, enabling users to systematically explore blocking-driven socio-economic and environmental impacts.
By offering a user-friendly community-driven tool, BLOCS can be used to bridge traditional meteorological approaches with data-driven methods, provide a benchmark for assessing the prediction of extreme weather events, address critical gaps in atmospheric blocking research, and ultimately advance our understanding of these phenomena and their role in shaping extreme events.
Acknowledgements: This work is supported by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC): UIDB/50019/2025 and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020). M. M. Lima was supported through the PhD MIT Portugal MPP2030-FCT programme grant PRT/BD/154680/2023. Additional support comes from the EU-funded H2020 project CLINT (Grant Agreement No. 101003876), and MALONE (PID2021-122252OB-I00), funded by MICIU/AEI/10.13039/501100011033 and ERDF, EU.
How to cite: M. Lima, M., M. Sousa, P., Fuentes-Alvarez, T., Ordóñez, C., García-Herrera, R., Barriopedro, D., M. M. Soares, P., and M. Trigo, R.: Systematic approach for global identification of extreme weather events associated with atmospheric blockings and subtropical ridges, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6112, https://doi.org/10.5194/egusphere-egu25-6112, 2025.
Multi-year droughts pose a significant threat to the security of water resources, putting stress on the resilience of hydrological, ecological, and socioeconomic systems. Motivated by the recent multi-year drought that affected Southwestern Europe and Italy from 2021 to 2023, here we utilize two indices - the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI) - to quantify the temporal evolution of the percentage of Italian territory experiencing drought conditions in the period 1901-2023 and to identify Widespread Multi-Year Drought (WMYD) events, defined as multi-year droughts affecting at least 30% of Italy. Seven WMYD events are identified using two different different precipitation datasets: 1921-22, 1942-43, 1945-46, 2006-08, 2011-13, 2015-19 and 2021- 23. Correlation analysis between the time series of Italian drought areas and atmospheric circulation indicates that the onset and spread of droughts in Italy are related to specific phases of the winter North Atlantic Oscillation (NAO), the Scandinavian Pattern (SCAND), East Atlantic/Western Russia (EAWR) pattern and of the summer East Atlantic (EA) and East Atlantic/Western Russia (EAWR) patterns. Event-based analysis of these drought episodes reveals a variety of atmospheric patterns and combinations of the four teleconnection modes that contribute to persistently dry conditions in Italy during both winter and summer. This study offers new insights into the identification and understanding of Italian WMYD events and serves as a first step toward a better understanding of the impacts of anthropogenic climate change on them.
How to cite: Pascale, S. and Ragone, F.: Widespread multi-year droughts in Italy: identification and causes of development, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6372, https://doi.org/10.5194/egusphere-egu25-6372, 2025.
Multi-year droughts (MYDs) are severe natural hazards that have become more common due to climate change. Given their significant societal impact compared to normal droughts (ND) of shorter duration, it is crucial to better understand the drivers of MYDs. In this work we used a combination of a large-ensemble of climate models and reanalysis data to study the difference between MYDs and NDs. For six different climatic regions, chosen to be of similar size to the dominating regional atmospheric circulation patterns, we used reanalysis data of precipitation and potential evapotranspiration to show the regional characteristics and drivers of MYDs and contrast these with characteristics of NDs. Our findings reveal that MYD occurrence and duration varies significantly between the regions, where relatively larger differences in duration between MYD and NDs can indicate different drivers resulting in the different drought durations. Regions with distinctive seasonality in their precipitation climatology tend to experience faster drought onsets compared to regions with climatologically steady precipitation. Furthermore, our analysis shows that MYDs and NDs often start with similar conditions but diverge over time, and that longer-term memory is present in some regions, which might provide avenues for the predictability of MYDs. However, since MYDs are rare events (2 to 6 MYDs per region between 1950-2023 in this study), we supplement reanalyis data with that of CMIP6 climate models with a large number of ensembles to assess the drivers of MYDs with more statistical rigour. This creates the opportunity to study the contributions of oceans, soil moisture, snow, and other climate variables on the persistent circulation patterns leading to MYDs, and to find the influence of climate variability on the occurrence of MYDs.
DOI: http://dx.doi.org/10.2139/ssrn.4974995
How to cite: van Mourik, J., Ruijsch, D., van der Wiel, K., Hazeleger, W., and Wanders, N.: Drivers of multi-year droughts in large ensemble simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8108, https://doi.org/10.5194/egusphere-egu25-8108, 2025.
Droughts are extreme events with major economic, social and environmental impacts, and it is crucial to be able to anticipate them. To improve their prediction on a seasonal timescale, it is essential to better understand the underlying conditions that precede them. In Europe, intra-seasonal to seasonal climatic variations are linked to atmospheric circulation and are weakly constrained by tropical teleconnections.
This study employs year-round weather regimes to demonstrate that the North Atlantic atmospheric circulation plays a fundamental role in precipitation deficits across Europe. Precipitation deficits are quantified using the reanalysed 3-month standardised precipitation index (SPI3). We use the SPI3 to define drought events and propose a new regionalisation of Europe, divided into regions with the same drought-related characteristics. We demonstrate that each weather regime is associated with a distinct precipitation pattern across regions, that remains relatively stable throughout the year. The representation of the regime-drought relationship in CMIP6 model simulations is then discussed.
How to cite: Savary, O., Ardilouze, C., and Cattiaux, J.: Linking European droughts to year-round weather regimes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1557, https://doi.org/10.5194/egusphere-egu25-1557, 2025.
Severe droughts in the Cape Town region (CTR) are projected to become more frequent in the coming decades, posing significant societal challenges. However, while climate models consistently predict a precipitation decline for the CTR until the end of this century, these projections carry substantial uncertainties, with decreases ranging from almost zero to as much as -50%.
In this study, we employ causal networks to evaluate climate models based on their ability to accurately represent the large-scale dynamical processes that drive precipitation in the CTR. While previous research has identified links between precipitation in the CTR and various large-scale drivers, such as the eddy-driven jet and sea surface temperatures in the South Atlantic, the interactions between these drivers remain poorly understood and the relative contributions of individual drivers to precipitation in the CTR remain unexplored.
Following causal inference theory, the causal relationships among the large-scale drivers of precipitation in the CTR are quantified in reanalysis data, pinpointing the main precipitation drivers, their interactions and relative contributions to precipitation and drought events. The resulting causal network is then applied to constrain precipitation projection. The study’s insights into the links between planetary-scale circulation patterns and regional processes could enhance our understanding of extreme and compound events, with potential implications for drought management.
How to cite: Friedel, M., Kretschmer, M., and Hewitson, B.: Using causal networks to constrain regional drought projections, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10214, https://doi.org/10.5194/egusphere-egu25-10214, 2025.
Since 2010 Easter Island (Rapa Nui) has experienced an exceptional decadal-scale megadrought. Observations show a significant and unusual decrease in precipitation on Rapa Nui: every year from 2010-2023 has had lower precipitation than the average from 1979-2009, resulting in an average precipitation that is 67% of normal. This reduction in precipitation coincides with decadal-scale climate shifts: an intensification of the South Pacific Anticyclone and its shift closer to the island along with a poleward shift of the Southern Hemisphere storm track. Each of these phenomena are trending near or beyond their most extreme values since 1979 and each of them are directly linked to reduced precipitation on Rapa Nui. These trends are shown to continue into mid-century under an intermediate greenhouse gas emissions scenario. We therefore argue that the current megadrought is best explained by anthropogenic climate change and that Rapa Nui may be entering a fundamentally drier climate state.
How to cite: Steiger, N. and Markovitz, E.: Contemporary Megadrought on Easter Island (Rapa Nui) since 2010 , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16474, https://doi.org/10.5194/egusphere-egu25-16474, 2025.
Droughts in Western Central Europe (WCE) have recently attracted attention due to their detrimental impact on crops, ecosystems, and society, as evidenced by events in 2018 and 2022. In this region, however, their variability and underlying causes remain unclear. This study aims to associate droughts with the atmospheric circulation to gain insight into their drivers. We employed reanalysis datasets (ERA5, 20CRv3, and ModE-RA) to identify meteorological drought events using the Standardized Precipitation Evapotranspiration Index at a 3-month scale and consistently connect them to atmospheric circulation patterns through k-means clustering. The three datasets are evaluated over the WCE regions, showing that they are highly reliable over periods ranging from 70 to 180 years, providing a long perspective on the recent events. Firstly, we demonstrate that droughts in WCE display a strong multidecadal variability with no significant long-term trend. Although precipitation has increased over time, this has been offset by the rising atmospheric evaporative demand due to warming. Secondly, we identify three distinct atmospheric circulation patterns associated with drought events in WCE: a high-anomaly geopotential height centred over Western Central Europe (WCE+); a dipole of high-anomaly geopotential height over the British Isles and low-anomaly geopotential height over the Maghreb (BIM+); and the negative phase of the North Atlantic Oscillation (NAO-), predominantly in winter. Our analysis shows that droughts have become increasingly associated with WCE+ over the last century, while their association with NAO- has decreased over the past 180 years. This research provides a regional historical analysis of meteorological drought and its drivers, offering better insight into long-term regional climate change.
How to cite: Neimry, E., Goosse, H., and Jonard, M.: Connecting Drought Events with Atmospheric Circulation Patterns in Western Central Europe: A Historical Perspective, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-478, https://doi.org/10.5194/egusphere-egu25-478, 2025.
With the significant warming, Central Asia (CA) has suffered from frequent drought events and vegetation degradation. However, whether it is the large-scale circulation dynamics or the surface local thermal mechanism that plays the dominant role in the drought remains unknown. Here we used 3-month Standardized Precipitation Evaporation Index in August to identify the summer drought events for 1980-2022 and conducted a composite analysis. Results indicate that the drought related wave train, originating from mid-high latitude North Atlantic (NA), has a barotropic vertical structure and propagates eastward, featuring a positive geopotential height center in CA. The pronounced warm sea surface temperature (SST) over the middle-latitude NA and cold SST over the high-latitude NA contribute to the Rossby wave formation, which is verified by an analysis of the apparent vorticity anomaly and linear baroclinic model experiments. The anticyclone anomaly over CA, corresponding to strong vertical subsidence, enhances downward shortwave radiation and surface sensible heat flux, while significantly reducing surface latent heat flux. The maintenance of drought is usually associated with persistent precipitation deficits. By using the backward moisture tracking model, we further found that the recycled precipitation, induced by the local evapotranspiration, contributes to the 88.39% reduction of total precipitation during drought periods, whereas the inflow of external advected moisture shows no significant decrease. The above results highlight the dominated role of local land-atmosphere interactions responsible for the drought through reduced local evapotranspiration, with large-scale circulation anomalies providing a conducive background for the drought.
How to cite: Ren, Y. and Yu, H.: Impact of Mid-high Latitude Circulation and Surface Thermal Forcing on Drought Events in Central Asia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2533, https://doi.org/10.5194/egusphere-egu25-2533, 2025.
Rainfall intensification due to planetary warming is increasingly impacting nearly all regions of the globe. South America is no exception with unprecedented landslides (São Sebastião, February 2023) and river catchment-scale flooding (Rio Grande do Sul, September 2023 and May 2024) being observed more frequently. Over South America, tropical-extratropical cloud bands in the South Atlantic Convergence Zone (SACZ) produce most of the rainy season precipitation. Droughts can occur in years with fewer SACZ events while intensely raining clusters within the cloud bands can trigger flash floods and landslides. Here, we diagnose the impacts of future precipitation intensification on the frequency and intensity of SACZ tropical-extratropical cloud bands using the first-of-its-kind continental-scale convection-permitting climate simulation. While cloud bands will see a future 20-30\% decrease in their frequency, intense events with a likelihood of 1-in-5 in the present day will become more frequent in the future, with 3-in-5 likelihood, increasing the risk of heavily raining clusters. This tripling in intense cloud band frequency results from intensified mesoscale rainfall structures within the continental-scale cloud bands, a risk better captured by convection-permitting models. Geographically, the intensification of mesoscale rainfall structures is most prevalent in the highly populated coastal regions of Southeastern and Southern Brazil, areas already highly exposed to extreme weather events, floods, and landslides. This increased risk significantly exceeds the projections from traditional climate models with convection parametrizations and highlights the growing risk of intense cloud-band rainfall over South America under warming.
How to cite: Zilli, M., Hart, N., Halladay, K., and Kahana, R.: Increased frequency of intense South Atlantic Convergence Zone-related cloud band events by 2100 in convection-permitting simulation , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17349, https://doi.org/10.5194/egusphere-egu25-17349, 2025.
Cut-off lows (COLs), which are warm season high altitude cold depressions originating from the pole, have lead to the most extreme precipitation events in Belgium in the past decades, notably in July 2021. Their frequency is expected to rise with Global warming due to slowing dynamics during the warm season. On top of this, extreme precipitation events are becoming more frequent, and more extreme due to the increase of atmospheric moisture content resulting from its warming (Brajkovic et al., 2025 in prep.). To understand the cause of this increased frequency, we want to assess the evolution of the frequency of COLs which lead to extreme precipitation events in Belgium.
First, over 1940-2023, using our bias-adjusted high-resolution (5-km) Regional Climate model MAR (Modèle Atmosphérique Régional) precipitation data over Belgium and ERA5 reanalysis 500hPa geopotential data over Europe, we identify COLs which lead to extreme precipitation over the country. We find COLs leading to extreme precipitation all over the period. Their occurence has increased over the last decades reaching a frequency of 1 COL per year. However, we find periods with less COLs like in the 1970s.
Second, MAR is forced 6 CMIP6 Earth System Models over 2015-2100. Four Shared Socioeconomic Pathways baseline scenarios (SSP) are used ranging from low-end (SSP1-2.6) to high-end emissions (SSP5-8.5). Again, using ESM 500hPa geopotential and bias-ajusted MAR precipitation data, we proceed to the same detection over the future. We find that the occurrence of COLs is stochastic and without clearly identified trends. Intense precipitation events occur irrespective of the scenario at timings which are challenging to predict. However, the frequency of COLs reaches 1 COL per year irrespective of the model or of the scenario. This analysis shows that a large amount of the uncertainty over future computed extreme precipitation statistics lies in the occurrence of COLs.
How to cite: Brajkovic, J., Fettweis, X., Ghilain, N., and Doutreloup, S.: Past and future evolution of synoptic weather patterns leading to extreme precipitation events in Belgium. Linking synoptic scale events to their local impacts. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9805, https://doi.org/10.5194/egusphere-egu25-9805, 2025.
The El Niño-Southern Oscillation (ENSO) influences the global temperature and precipitation patterns. Generally, the ENSO influence has been related to its amplitude. We use information-theoretic generalization of Granger causality to observe the causal influence of phases of ENSO oscillatory components on scales of precipitation variability in Yangtze and Yellow River basins, with a focus on its quasi-oscillatory dynamics spanning various timeframes. We find that the ENSO quasi-biennial component has a causal effect on precipitation variability on and around the annual scale, while the amplitude of the precipitation quasi-biennial component is controlled by low-frequency ENSO components with periods of around 6 years. This cross-scale causal information flow is particularly noticeable in the Yellow River basin, whereas in the Yangtze River basin, the ENSO amplitude has the greatest causative effect. The provided results indicate that different components of ENSO dynamics should be used to predict precipitation in different regions.
This study is supported by the Czech Academy of Sciences, Praemium Academiae awarded to M. Paluš.
Latif, Y., Fan, K., Wang, G., & Paluš, M. (2024). Cross-scale causal information flow from the El Niño–Southern Oscillation to precipitation in eastern China. Earth System Dynamics, 15(6), 1509-1526
How to cite: Latif, Y., Fan, K., Wang, G., and Paluš, M.: A cross-scale causal information flow from the El Niño–Southern Oscillation to precipitation in the Yangtze and Yellow River basins, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17086, https://doi.org/10.5194/egusphere-egu25-17086, 2025.
Extreme precipitation occurs under specific atmospheric circulation patterns. In this talk, we show the connection of extreme precipitation in central eastern China to the East Asian jet stream changes during June, the month with frequent occurrence of extreme precipitation. Two types of distinct East Asian jet stream configurations are detected for the occurrence of extreme precipitation. One is a latitudinal shift of the East Asian jet stream and the other is an intensification of the East Asian jet stream. The former corresponds to extreme precipitation to south of the Yangtze River and the latter corresponds to extreme precipitation along the Yangtze River. The changes in the location and intensity of the East Asian jet stream are associated with meridional wave patterns along East Asia and zonal wave patterns over mid-latitude Eurasia. The role of the western North Pacific subtropical high is robust but relatively larger for extreme precipitation south of the Yangtze River. The South Asian high plays an important role for extreme precipitation south of the Yangtze River, but its role is weak for extreme precipitation along the Yangtze River. Wind-induced temperature anomalies modulate the vertical change of the meridional height gradient over eastern China and thus contributes to the latitudinal shift and intensity change of the East Asian jet stream.
How to cite: Wu, R., Zhu, P., He, P., and Zhang, W.-J.: Linking extreme precipitation during June in central eastern China to the East Asian jet stream changes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2403, https://doi.org/10.5194/egusphere-egu25-2403, 2025.
Abstract. Western Ukraine has encountered significant challenges due to three extensive summer rainfall events and major floods in July 2008, July 2010, and June 2020, resulting in numerous fatalities and substantial economic damage. This study investigates the hydrometeorological factors, as well as the atmospheric processes, that led to these three devastating flood events in the basins of the Tisza, Prut, Siret, and Dniester rivers in western Ukraine. The 2008 flood was the most severe, with river levels surpassing historical records. The flood in 2020 was notable for its hydrological complexity and was evolving more rapidly than the 2008 flood. The 2010 flood was more localized.
A series of intense precipitation events extending over about 5 days were one of the key factors resulting in floods in all three cases. The prolonged heavy precipitation that caused these floods mainly occurred during the transition of the large-scale flow from a Scandinavian blocking pattern to a western Russian blocking regime and typically formed beneath an upper-level trough located over southeastern Europe. An essential synoptic feature for initializing the heavy rain events was a quasi-stationary upper-level cutoff low that existed for about 5 days. This persistence of the synoptic flow pattern allowed for the advection of warm, moist air from the Black Sea at low to mid-tropospheric levels toward the eastern slopes of the Carpathians, leading to orographic lifting that strongly contributed to precipitation in the region. While each flood event shared common mechanisms, such as Rossby wave breaking with subsequent formation of cutoff lows, atmospheric blocking and orographic lifting, the arrangement, interaction, and intensity of these processes varied. The 2010 event was marked by a combination of two consecutive Rossby wave breaking events and an intense atmospheric block in western Russia. In contrast, the 2008 and 2020 floods were characterized by a merging of the Scandinavian blocking regime with a blocking system over western Russia, resulting in the formation of a cutoff cyclone over Romania. Thus, through the characterization of hydrometeorological conditions during western Ukraine floods, we aim to provide knowledge for better preparedness for future floods both in the region and throughout Eastern Europe.
How to cite: Agayar, E., Armon, M., and Wernli, H.: The catastrophic floods in 2008, 2010 and 2020 in western Ukraine: Hydrometeorological processes and the role of upper-level dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5086, https://doi.org/10.5194/egusphere-egu25-5086, 2025.
Accurately estimating the risks of weather-related impacts requires comprehensively simulating weather conditions that could occur but have not occurred in the historical record. This is the aim of weather generators. Analog-based weather generators exploit the fact that the large-scale atmospheric circulation constrains regional weather and generate multivariate spatiotemporal meteorological fields by resampling historical data. During the resampling, constraints are employed to ensure that successive samples have consistent circulation patterns. Compared to other types of weather generators, resampling-based methods have the advantage that dependencies between variables and between locations are automatically correctly captured. However, the generated time series are limited to observed ranges, and even “close” analogs in the historical record are relatively far away from each other.
We overcome these limitations by constructing a (daily) analog weather generator using ECMWF extended ensemble forecast hindcast (re-forecast) data, which provides a much larger sample size and the ability to sample values larger than the observed records. We choose this dataset because it has high spatial resolution and provides a large set of states from a relatively constant climate, while model biases remain limited because the forecasts are initialized from reanalysis data. With the ensemble hindcasts, we can also assess how “close” analogs are compared to typical ensemble spreads. We test our methodology by applying it to simulate weather over a European domain. Analogs are defined in terms of geopotential height at 500hPa and computed over an extended region including parts of the North Atlantic. With our approach, we can find better analogs compared to a baseline using only ERA5 data. We evaluate key properties of the simulated time series, such as their annual cycle, extremes, and lengths of wet and dry spells. The weather generator can be widely applied to estimate potential climate impacts, for instance with impact models. It is especially useful in cases where an accurate representation of dependencies between variables or across space is important for the impacts, which is the case for a number of different types of compound events.
How to cite: Wider, J., Klotz, D., and Zscheischler, J.: An analog-based weather generator using re-forecast data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11855, https://doi.org/10.5194/egusphere-egu25-11855, 2025.
The tropical cyclones are one of the biggest hazards to life and socio-economic activities even in the formative stages of their development. Some of their main features, especially in the shape evolution and in the dynamics, are common with events that in recent years are increasingly affecting the Mediterranean basin, defined as Mediterranean Tropical-Like Cyclones (MTLCs), or Medicanes.
In this study, we investigate the spatial and temporal properties of two Medicanes through high spatial resolution (1 km) reanalysis-based numerical simulations, generated using the Weather Research and Forecasting (WRF) model. The events examined are Qendresa (occurred in November 2014) and Ianos (occurred in September 2020), both developing over the Mediterranean Sea.
The WRF reanalyses were also used to conduct sensitivity studies on the parameterizations of atmospheric physics, focusing on PBL, radiation and microphysics schemes.
In order to address the problem in the classical fluid turbulence picture, the results were also analyzed using the Proper Orthogonal Decomposition (POD) method. With the aim of providing a first approach to understand how different contributions, operating on distinct spatio-temporal scales, can influence the local dynamics and the evolution of the medicanes. In addition the analysis will uncover the formation of coherent structures in the extreme event maturation.
How to cite: Gencarelli, C. N., Primavera, L., Ciardullo, G., Settino, J., and Carbone, F.: Numerical investigations of turbulence in Mediterranean cyclone events: insights from the Turbimecs project, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4406, https://doi.org/10.5194/egusphere-egu25-4406, 2025.
This study examines how the Madden-Julian Oscillation (MJO) phases affect afternoon diurnal convection (ADC) patterns in Sri Lanka during 2001-2020. Sri Lanka experiences the highest frequency of ADC events in the Indian subcontinent region while located in a pivotal position within the propagation pathway of the MJO. To address the research gap regarding the MJO’s impact on seasonal diurnal rainfall in Sri Lanka, we analyze both the spring and autumn seasons, which are the two seasons with greater diurnal rainfall variability, focusing on strong MJO phases (P1-P8). Our findings show that daily rainfall increases during the P2-to-P3 phases and decreases during the P6-to-P7 phases in both seasons. The diurnal rainfall patterns, however, show seasonal differences. In spring, the diurnal rainfall amplitude peaks during P2-to-P3 phases, while in autumn, it peaks during P8-to-P1 phases. ADC events are more frequent and intense during these respective phases. The MJO's effect on both diurnal rainfall amplitude and ADC events is stronger in autumn compared to spring. During active MJO phases, we observe enhanced westward propagation of diurnal rainfall linked to ADC events, driven by moisture convergence and increased upward motion. The combination of mid-to-upper level easterly winds and deep convection over Sri Lanka leads to more distinct westward propagation during P2-to-P3 phases in spring and P8-to-P1 phases in autumn. These findings enhance our understanding of how the MJO influences local rainfall patterns and can aid in improving regional weather forecasting.
How to cite: Huang, W.-R., Koralegedara, S. B., Chiang, T.-Y., Lee, C.-A., Tung, P.-H., Chien, Y.-T., and Deng, L.: The Impact of the Madden-Julian Oscillation on Spring and Autumn Afternoon Diurnal Convection in Sri Lanka, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2668, https://doi.org/10.5194/egusphere-egu25-2668, 2025.
Increasing temperatures due to climate change pose challenges to countries worldwide, including Brazil, where extreme weather may result in biodiversity loss, water resource availability changes, and significant economic and health impacts. This study evaluates the influence of various teleconnection indices on the variability patterns of atmospheric blocking events occurring in central Brazil and episodes of the South Atlantic Convergence Zone (SACZ). Nearly all teleconnection indices made available in the NOAA’s website were analysed, including those related to the Pacific, Atlantic, Indian Oceans and global-scale indices. Additionally, four new indices were explicitly developed for this study, focusing on NOAA’s OISST Sea Surface Temperature anomalies in the North Atlantic Ocean near the Moroccan coast. The characterization of atmospheric blocking events and SACZ episodes was carried out using indices developed at LAMMOC/UFF, which effectively capture the behaviour of these atmospheric systems across different regions of Brazil. The SACZ index was calculated using NCEP Reanalysis data, while the atmospheric blocking index used ERA5 reanalysis data, resulting in a time series spanning from 1981 to 2023. All data were normalized for statistical analyses, and methods including Pearson’s correlation coefficient, Principal Component Analysis, K-means clustering techniques, trend analysis, and the Mann-Kendall test were applied to identify and quantify trends in the data. Atmospheric blocking and SACZ episodes have contrasting yet significant influences on the rainfall in central Brazil. Atmospheric blocking events are typically associated with prolonged droughts, whereas SACZ episodes are linked to intense and spatially well-distributed precipitation. This region is vital for the country’s agriculture, industry, and energy production. The analysis revealed that a significant portion of oceanic indices from the Atlantic and the Pacific Oceans, along with atmospheric blocking events, exhibit strong increasing trends. These trends are accompanied by positive correlations, observed in the trend-inclusive and detrended series. For instance, correlations reach 0.7 values with the Global Mean Land/Ocean Temperature, 0.45 with ENSO indices, 0.55 with North Atlantic indices near the Moroccan coast, and 0.67 with the Pacific Warmpool Area Average. In contrast, the SACZ index showed no clear trend in the Mann-Kendall tests. Correlations between SACZ and the same oceanic indices often exhibited an inverse relationship compared to those with blocking indices and were also generally weaker, ranging between -0.15 and -0.30. One exception was a positive correlation of around 0.34 with the East Pacific/North Pacific Oscillation index. Overall, the study highlights that atmospheric blocking events are becoming increasingly frequent and intense in central Brazil, closely following the warming trend of the oceans. This poses a warning for the region’s hydrometeorological regime. While the absence of an evident decline in SACZ episodes provides some relief, the escalating deforestation in the Amazon, one of the primary sources of moisture driving precipitation during SACZ episodes, may become the decisive factor in altering the region’s precipitation patterns, potentially exacerbating the ongoing water crisis in central Brazil.
How to cite: Sancho, L., Aguiar, L., Victalino Galves, V. L., Esposte Coutinho, P., and Cataldi, M.: The Role of Teleconnection Indices in Modulating Rainfall and Drought in Central Brazil, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11026, https://doi.org/10.5194/egusphere-egu25-11026, 2025.
The western North Pacific anomalous anticyclone (WNPAC) often exists during the mature and decaying phases of El Niño, significantly affecting the East Asian summer monsoon. Previous studies have revealed the importance of the Indian, Pacific, and Atlantic Oceans in generating and maintaining the WNPAC. However, a quantitative comparison of the contributions from these three oceans is still lacking. This study uses pacemaker experiments with a state-of-the-art model to quantify the relative contributions of the three tropical oceans to the interannual WNPAC variability. We find that the Pacific accounts for over 50% of the interannual variance in boreal winter and the following spring, while the roles of the Atlantic and Indian Oceans become more pronounced in spring. In summer, all three oceans contribute significantly and equally. The Indian Ocean SST is influenced by remote forcing from the Pacific Ocean, while the Atlantic Ocean operates more independently, with no evident effect from other oceans.
How to cite: Lu, Z., Dong, L., Song, F., Wu, B., Wu, S., and Wang, C.: Quantifying Relative Contributions of Three Tropical Oceans to the Western North Pacific Anomalous Anticyclone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3062, https://doi.org/10.5194/egusphere-egu25-3062, 2025.
Renewable energy sources are inherently influenced by environmental variability. In Brazil, hydropower constitutes approximately 65% of the country’s electricity matrix, relying directly on river flow, which is strongly governed by precipitation on an operational timescale. This study investigates the influence of atmospheric blocking events and episodes of the South Atlantic Convergence Zone (SACZ) on the occurrence and magnitude of natural flow in several hydropower plants in river basins across Brazil. Atmospheric blocking and SACZ episodes were characterized using indices developed at LAMMOC/UFF, which effectively capture the behavior of these systems in different regions of the country. The SACZ index was calculated using NCEP reanalysis data, while the blocking index was derived from ERA5 reanalysis data. Natural flow data for the power plant areas were provided by the National Electric System Operator (ONS). To maximize the availability of records for this study, the time series was defined from 1960 to 2023. All data were normalized for statistical analyses, and methods such as Pearson’s correlation coefficient, Principal Component Analysis (PCA), K-means clustering, trend analysis, and the Mann-Kendall test were employed to identify and quantify trends. Results indicate that blocking events have shown a rising trend across all evaluated regions, whereas SACZ episodes do not display an increasing trend uniformly throughout the country. Regarding river flow trends, increases were observed in Southern Brazil, while decreases predominate in the Southeast, Central-West, Northeast, and North regions. SACZ episodes positively influence flow in hydropower plants in the Central-West, North, and Northeast regions, while inhibiting precipitation in the South as their effects shift northward, away from the basins. For instance, the Paranaíba River basin in the Northeast shows a correlation of 0.55 with SACZ episodes, and the Paraopeba River basin located between the Southeast and Central-West Regions, presents a correlation of 0.57. Notable SACZ-related correlations are also observed in the Grande, Paranaíba, and Baixo Paraná basins, with values exceeding 0.3 and increasing towards the South, reaching over 0.5 for Baixo Paraná and 0.6 for Grande and Paranaíba basins. Conversely, the Araguaia-Tocantins basin in the North exhibits one of the highest correlations, at 0.69. Atmospheric blocking events, in turn, are positively correlated with river flow in the South, particularly in the Uruguai and Jacuí basins, which exhibit the highest correlation values. However, they produce a negative correlation in basins of other regions, as their associated high-pressure systems inhibit atmospheric dynamics, reduce precipitation, and prevent the advance of cold fronts, concentrating precipitation in Southern areas. The results reveal a decline in river flow across most hydropower plant areas, posing risks to Brazil’s electricity production, with potential impacts on the country’s Gross Domestic Product (GPD). SACZ and atmospheric blocking events significantly influence river flow, especially in the power plants of the Central-West, North, and Northeast regions. Developing indices for these atmospheric phenomena offers valuable insights into regional water availability, supporting strategies to mitigate risks from shifting precipitation regimes across Brazil’s diverse climates and biomes.
How to cite: Esposte Coutinho, P., Sancho, L., da Fonseca Aguiar, L., Victalino Galves, V. L., Zanandrea, F., and Cataldi, M.: Impacts of Atmospheric Phenomena on River Flow and Hydropower Stability in Brazil, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12052, https://doi.org/10.5194/egusphere-egu25-12052, 2025.
Thermal season variations contribute to shaping natural hydrological processes in Nordic regions. Although changes in seasonal hydro-climatological factors due to global warming at both global and regional scales have been widely studied, there remains a limited understanding of the timing characteristics of these seasonal shifts. Given the critical role of the annual temperature transition from the cold to the warm phase in controlling hydrological events in Nordic regions, this research focuses on the temporal variation of the thermal spring season across Finland. We investigate how the timing of the thermal spring has changed over the past six decades across Finland and how the changes vary spatially. We also identify temporal turning points in these transitions.
This research utilizes high-resolution (1x1 km) daily mean temperature data over Finland, spanning past six decades, publicly provided by the Finnish Meteorological Institute. Several indices were calculated based on a fixed thermal threshold to track both spatial and temporal variations in the thermal spring season, and to identify possible trends and correlations using various statistical methods. Temporal changes in the indices were analyzed using Mann-Kendall test, while the Theil-Sen estimator was applied to determine the slope of the observed trends. To mitigate the influences of potential autocorrelation in the dataset, the Trend-Free Pre-Whitening (TFPW) method was employed. For spatial analysis, Empirical Orthogonal Function (EOF) decomposition was used to identify dominant spatial pattens. To separate significant physical signals from noise in the estimated spatial patterns, the North significance test was used. Furthermore, the Pettitt test was applied to assess the turning points in spatial behavior of timing indices. By analyzing an extensive dataset covering Finland, coupled with a long data period, this research provides valuable insights into temporal shifts in the thermal spring season and their potential connections to other hydro-climatological factors.
How to cite: Kaboli, S., Kankare, V., Torabi Haghighi, A., Bertacchi Uvo, C., and Kasvi, E.: Changes in the Timing of the Thermal Spring Season Across Finland and Its Turning Point Over the Past Six Decades., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17361, https://doi.org/10.5194/egusphere-egu25-17361, 2025.
In this study, the interdecadal variation of extreme precipitation in May over southwestern Xinjiang (SWX) and related mechanisms were investigated. The extreme precipitation in May over SWX exhibited a decadal shift in the 1990s (negative phase during 1970–86 and positive phase during 2003–2018). The decadal shift corresponded to strengthened moist airflow from the Indian Ocean and an anomalous cyclone over SWX during 2003–2018. It is found that the interdecadal change of the wave trains in Eurasia might account for the differences in atmospheric circulation between the above two periods. Further analyses reveal that spring snow cover over Eurasia is closely linked to extreme precipitation over SWX during 2003–2018. Increased snow cover in western Europe (WE) from February to March is accompanied by more snowmelt. This resulted in less local snow cover and lower albedo which lead to warm temperature over WE in May. The changes in temperatures increase the local 1000–500-hPa thickness over WE. These factors provide favorable conditions for the enhancement of the Eurasian wave trains which significantly influence extreme precipitation over SWX. On the other hand, corresponding to decreased albedo caused by the reduction of northern Eurasia (NE) snow cover in May, anomalous surface warming occurs over NE. The anomalous warming result in positive geopotential height anomalies which intensifies the meridional geopotential height gradient over Eurasia and causes an acceleration of the westerly jet in May. Anomalous upper-level divergence in SWX induced by the enhanced westerly jet provides a favorable dynamical condition for increased extreme precipitation.
How to cite: Chen, P. and Li, W.: Increased extreme precipitation in May over southwestern Xinjiang in relation to Eurasian snow cover in recent years, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-58, https://doi.org/10.5194/egusphere-egu25-58, 2025.
Under global warming, the occurrence of compound extreme weather and climate events has increased, resulting in profound ecological and societal damages. Understanding the forming mechanisms of these events is imperative for formulating effective mitigation and adaptation strategies. This research focuses on causality of the compound extreme heat and precipitation events (CEHPEs) in northeastern China. From 1961 to 2018, a total of 55 heatwave events occurred in this region, with 18 identified as the CEHPEs.
The formation of CEHPEs in northeastern China is closely related to the southeastward propagating quasi-barotropic anomalous anticyclone. As the center of the anomalous anticyclone approaches northeastern China, the associated descent reduces the cloud cover and increases downward shortwave radiation. The thus-heated ground increases the upward longwave radiation and sensible heat, predominantly warming the surface air and causing the heatwave. During the development of the heatwave, the increased lower-level moisture due to the enhanced surface evaporation and the increased column moist static energy due to the warming air temperature destabilize the atmosphere. When the anomalous anticyclone moves out of northeastern China after the heatwave, intense convection rapidly develops, resulting in extreme precipitation and completing the CEHPEs.
Comparison between the CEHPEs and the mere heatwave events is also conducted. The major difference resides in the zonal scale of the anomalous anticyclone. In the CEHPEs, the anomalous anticyclone has a small zonal scale and decays locally due to the advection by the climatological westerly acting on the zonal gradient of anomalous vorticity. In contrast, the zonal scale of the anomalous anticyclone in the mere heatwave events is much larger, which slowers the decaying due to the weaker zonal advection and thus impedes the convection development and extreme precipitation.
How to cite: Yang, Y.: Causality of Compound Extreme Heat-Precipitation Events in Northeastern China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1872, https://doi.org/10.5194/egusphere-egu25-1872, 2025.
In this study, we clarify the role of a distinguished weather pattern over Siberia that has contributed to intense summer precipitation across East Asia, particularly in recent decades. This weather pattern, termed the Siberian Summer Cold Wave (SSCW), is defined through rigorous criteria and retrospective case selection. SSCW is characterized by the rapid influx of cold air from the Siberian region into East Asia during summer, which is associated with an increase in the potential temperature gradient, leading to the development of precipitation. Since the early 2000s, the frequency of SSCW events has increased, coinciding with a rise in severe precipitation events, underscoring its significance. Although SSCW has played a crucial role in influencing precipitation in East Asia, previous studies have predominantly focused on mechanisms related to heavy rainfall occurring in southern regions of East Asia. Consequently, there has been a relative lack of research investigating systems contributing to heavy precipitation from the north. This study provides a comprehensive analysis of SSCW events and elucidates their precipitation characteristics, positioning SSCW as a pivotal precipitation pattern within the East Asian summer climate. Our findings highlight the need for continued research to better understand SSCW dynamics and effectively mitigate associated risks.
How to cite: Han, K., Kim, B.-M., Ku, H.-Y., Noh, H., Jeong, J.-H., and Woo, S.-H.: Role of the Siberian Summer Cold Wave in Intensifying East Asian Summer Precipitation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15158, https://doi.org/10.5194/egusphere-egu25-15158, 2025.
Precipitation in Central Europe can be classified as stratiform or convective based on its origin. Heavy convective precipitation is associated with intense storms, develops rapidly in localized areas, and can cause flash floods. In contrast, heavy stratiform precipitation is linked to longer-lasting, less intense rainfall events that may lead to large-scale flooding. These two types of precipitation also differ in their causal conditions, such as atmospheric circulation patterns and thermodynamic properties.
This study analyses heavy precipitation using time series from 19 observation stations across the Czech Republic for the period 1982–2021. An algorithm based on SYNOP reports was applied to classify precipitation totals as either convective or stratiform. Days with heavy precipitation (totals exceeding the 90th percentile) were assigned a circulation type using the Jenkinson & Collins (1977) method. This approach identifies 27 circulation types based on three indices: flow direction, strength, and vorticity.
The circulation types associated with heavy precipitation vary by season, precipitation type, and station location. Across all seasons, heavy precipitation is predominantly linked to cyclonic circulation and directional types with westerly and northerly flow components. In summer, heavy convective precipitation is additionally associated with anticyclonic conditions and unclassified patterns.
As climate change may significantly alter the atmospheric conditions driving heavy precipitation, understanding these phenomena and projecting their future behaviour is essential. To achieve this, the regional climate model ALADIN-CLIMATE/CZ operated by the Czech Hydrometeorological Institute will be used to evaluate the future relationship between heavy convective and stratiform precipitation and atmospheric circulation.
How to cite: Beranova, R. and Rulfová, Z.: Heavy convective and stratiform precipitation and their links to atmospheric circulation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6295, https://doi.org/10.5194/egusphere-egu25-6295, 2025.
This study presents a revised Tropical Cyclone Genesis Potential Index (χMqGPI) for projecting tropical cyclone genesis in the Western North Pacific (WNP) and evaluates its performance against the traditional χGPI index. Using simulations from 22 CMIP6 models, both indices were calculated and assessed for their accuracy in historical and future warming scenarios. The results indicate that in historical simulations, both χGPI and χMqGPI exhibit strong correlations with observed tropical cyclone data, with correlation coefficients exceeding 0.9. Both indices also effectively capture the primary genesis regions of tropical cyclones in the WNP in terms of spatial distribution.
Under future warming scenarios, however, the two indices project contrasting trends in tropical cyclone genesis frequency (TCGF). χGPI consistently predicts an increase in TCGF, while χMqGPI projects a declining trend that aligns more closely with recent findings from high-resolution models. This declining trend underscores the robustness and reliability of χMqGPI in climate projections.
Decomposition analysis of χMqGPI revealed that large-scale dynamic parameters, particularly absolute vorticity and vertical wind shear, are critical in explaining discrepancies between model simulations. These differences become increasingly pronounced with the severity of warming, highlighting the importance of accurately representing large-scale environmental dynamics in models to improve tropical cyclone projections under climate change.
These findings offer valuable insights into the potential future behavior of tropical cyclones and emphasize the significance of adopting refined indices, such as χMqGPI, for reliable climate predictions. This work underscores the critical role of advanced metrics in understanding the impact of global warming on tropical cyclone activity in the WNP and beyond
How to cite: Hsiao, L.-P. and Hsu, H.-H.: Evaluating the Impact of Global Warming on Tropical Cyclone Genesis in the Western North Pacific: A Comparative Study of Tropical Cyclone Genesis Indices Using CMIP6 Models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7700, https://doi.org/10.5194/egusphere-egu25-7700, 2025.
Observations show that anticyclonic circulation anomalies over the subtropics associated with North Pacific Oscillation (NPO) in December are responsible for surface warming in East Asia of the following January, a 1-month lag. We demonstrate that the lagged impacts of December NPO anomalies on the East Asian surface warming in January are attributable to two possible pathways by way of the tropics-extratropics teleconnections and local air-sea interactions. The northeasterly anomalies along the southern edge of the December NPO-related anticyclonic circulation anomalies efficiently advect dry air towards the western North Pacific (WNP), leading the intensified negative precipitation anomalies from December to January. This results in a Rossby wave propagation forced by upper-tropospheric divergence in the WNP, and thus affects the persistence of anticyclonic anomalies over East Asia into January. Over the Kuroshio region the easterly anomalies along the southern edge of the December NPO anticyclonic circulation anomalies oppose the prevailing westerly winds. The significant weakening of wind speeds, which in turn give rise to sea surface temperature (SST) warming along the Kuroshio region as a result of wind-evaporation-SST feedback, lead to favorable conditions for the East Asian warming in January. Additionally, the Coupled Model Intercomparison Project Phase 6 (CMIP6) models reasonably simulate the delayed impacts of December NPO anomalies on the East Asian climate in January supporting observations.
How to cite: Kim, S. and Yoo, J. H.: Delayed impacts of NPO on wintertime surface air temperature in East Asia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7615, https://doi.org/10.5194/egusphere-egu25-7615, 2025.
Climate change is expected to amplify extreme-rainfall intensity and frequency over Europe due to the increase in atmospheric moisture with warming, ensuing severe socio-economic impacts. The influence of future dynamic changes i.e. changes to atmospheric circulation patterns, on extreme-rainfall over Europe, on the other hand, remains unclear. Additionally, recent works point out that inadequate representation of regional circulation patterns by climate models may strongly impact their climate-change results over Europe (Vautard et al., 2023).
This study presents a methodology for assessing the dynamical and thermodynamical contributions to the changes in extreme daily rainfall based on the Lamb weather type classification and with an application over Belgium. Thereby, GCMs from CMIP6 are first sub-selected based on their ability to accurately represent the overall atmospheric circulation (Serras et al., 2024) and the atmospheric circulation during days of extreme rainfall. We find that models with a good circulation probability distribution do not necessarily feature a good circulation-probability representation when restricting to days with extreme rainfall events, and vice versa. This means that, for our purpose, additional to the model selection based on all days, a selection based on the circulation probability distribution during days of extreme rainfall is implemented. Additionally, the increase in extreme-rainfall intensity and likelihood at the end of century under the SSP3-7.0 scenario for Belgium, are driven by thermodynamic factors rather than dynamic changes. While the probability of extreme rainfall rises predominantly in fall and winter, the most significant intensity increases are projected for spring and summer.
- Vautard, R., Cattiaux, J., Happé, T., Singh, J., Bonnet, R., Cassou, C., ... & Yiou, P. (2023). Heat extremes in Western Europe increasing faster than simulated due to atmospheric circulation trends. Nature Communications, 14(1), 6803.
- Serras, F., Vandelanotte, K., Borgers, R., Van Schaeybroeck, B., Termonia, P., Demuzere, M., & van Lipzig, N. P. (2024). Optimizing climate model selection in regional studies using an adaptive weather type based framework: a case study for extreme heat in Belgium. Climate Dynamics, 1-23.
How to cite: Van Schaeybroeck, B., Schoofs, J., Vandelanotte, K., Van de Vyver, H., Van Der Sichel, L., Vandersteene, M., Serras, F., and van Lipzig, N. P. M.: The intensification of future extreme-rainfall events over Belgium and their dynamic and thermodynamic contributions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7953, https://doi.org/10.5194/egusphere-egu25-7953, 2025.
Summer heat waves are among the most severe natural hazards in the mid-latitudes and known to be strongly associated with anticyclonic activity. Despite their frequent occurrence, gaps remain in the understanding of the processes that drive persistent heat outbreaks during the lifetime and in the vicinity of some anticyclones. A closer look at the life cycles of these anticyclones could be beneficial for understanding the circumstances under which there is an increased likelihood of near-surface extremes.
To date, numerous studies have performed some form of feature tracking on anticyclones, but many are limited to a specific region or context, while those that take a broader view focus on climatology rather than individual life cycles.
In this work, mid-tropospheric anticyclones are identified though geopotential height anomalies, tracked over time and analyzed based on their shape, propagation speed and overlap with other atmospheric phenomena, such as heat waves, droughts and blocking. Using 40 years of northern hemisphere reanalysis data, a detailed track dataset for around 5900 individual anticyclones is examined. It is shown that the most extreme temperature anomalies are systematically more likely to be associated with anticyclones with longer life times. Furthermore there is evidence that the probability for a heat wave maximum is higher in the early and late phases of the anticyclonic life cycles, with the former (latter) being particularly true for shorter-lived (longer-lived) high pressure systems.
How to cite: Thomas, M. and Pfahl, S.: Exploring and characterizing the life cycles of tracked anticyclones on the northern hemisphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11580, https://doi.org/10.5194/egusphere-egu25-11580, 2025.
Heat extremes have severe impacts on human health, economies, and ecosystems. In particular in Europe, heatwaves are expected to become more frequent and intense with climate change, making it essential to understand and quantify the key factors driving these events, such as soil moisture deficits and atmospheric circulation. Further, global warming is likely not only to increase the frequency and intensity of heatwaves in the summer, but also in early autumn, highlighting the need to explore seasonal variations in their drivers.
We analyze heatwaves in Central Europe (45–55°N, 4–16°E) in the historical period (1950-2023) by quantifying atmospheric persistence and exploring the link between surface temperatures and atmospheric circulation patterns using dynamical system theory. This approach is further contextualized by an analysis of weather regimes representing the low-frequency variability of the atmosphere over the North Atlantic and Europe. Using ERA5 reanalysis data, we examine intra-seasonal variations of heatwaves during the extended summer months (May–September). Our results show an anomalously strong link between atmospheric circulation and surface temperatures on heatwave days. In July and August, an anomalously high persistence of the atmospheric circulation is found on heatwave days, associated with an enhanced frequency of Scandinavian and European blocking weather regimes. Moreover, we investigate additional drivers of heatwaves such as soil moisture, and examine the life cycle of heatwaves.
How to cite: Dillerup, I., Lemburg, A., Buschow, S., and Pinto, J.: Seasonality of Heatwaves in Central Europe: Insights from Dynamical Systems Theory and Weather Regimes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13453, https://doi.org/10.5194/egusphere-egu25-13453, 2025.
Spring in particular can carry impact-relevant extreme events over Europe, such as late frost or early summer heat. However, the dominating mechanisms and drivers of such temperature extremes in European springtime are currently not well understood. Across all seasons, one mechanism relevant for temperature extremes in Europe is atmospheric blocking. Unlike winter, where blocking is predominantly related to cold spells, and summer, where blocking is predominantly related to warm spells, spring is a transition period during which both cold and warm spells might be connected to blockings.
While this transition has been statistically analyzed before, available time series were limited, as was, in turn, the spatial analysis. Here, using ERA-5 and E-OBS for the period 1950-2023, with more than doubling the time series, we confirm existing literature on the statistics and the change of blocking patterns throughout the spring season, although our work indicates more early spring warm spells than previously found. The greater data availability also allows the spatial division into blocking regions, allows us to characterize the sensitivity of warm spell frequency to blocking location. We show that blockings over Scandinavia and the UK lead to Northern European warm spells. Comparing springtime occurrences of blocked and unblocked warm spell days shows that in Northern Europe, warm spells often occur simultaneously with blocking, whereas in Southern Europe, warm spells less frequently occur simultaneously with blocking. We identify temporal clusters of preferred occurrences of blocked or unblocked warm spell occurrences in Northern and Southern Europe to trace their seasonal drivers, thus indicating the potential for seasonal predictions of spring warm spells over Europe.
How to cite: Häfele, S., Baehr, J., Krieger, D., and Borchert, L.: Variability of spring temperature extremes in Europe, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17426, https://doi.org/10.5194/egusphere-egu25-17426, 2025.
This study investigates the synoptic and large-scale atmospheric circulation associated with extreme precipitation events (EPEs) that occurred during the period 1979-2023 in the Western Himalaya (WH). These EPEs are defined as days when the mean precipitation exceeds the 99th percentile threshold of daily precipitation for each month from 1979 to 2023 across all grid points in the Indian Himalayan region (Karakoram, WH, Central and Eastern Himalaya). The weather regimes associated with these events are then classified using K-means clustering of geopotential height at 500hPa and vertical integrated moisture flux components. We have identified six clusters and determined that EPEs linked to four of these clusters predominantly occur during the monsoon months, whereas the other two clusters are characterized by WD (Western Disturbance)-driven EPEs that appear in the winter months. The EPEs in cluster-1 are mainly driven by the low-pressure system (LPS) in the Bay of Bengal and Rossby-wave breaking (atmospheric blocking by Siberian anticyclone) in the upper-atmosphere along with the midlatitude forcing of North Pacific Oscillation (NPO) (positive phase). The EPEs in clusters 2 and 5 resulted from a break in the monsoon caused by the northward displacement of LPS close to the Himalayan foothills, along with an omega type of blocking with a strong anticyclone over the WH, which is located between two cyclones. The midlatitude forcings of the negative phase of NPO and the negative phase of ENSO during EPEs in clusters 2 and 5, respectively, support the occurrence of EPEs in the WH. The EPEs in cluster-6 occurred due to incursion of a WD into the WH, along the northward migration of LPS in the break-monsoon phase over the WH; tropical forcing of positive phase of ENSO promotes the EPEs in this cluster. The WDs-driven clusters (cluster-3 and 4) mainly support higher amount of precipitation over the WH, and account for 80-95% of mean precipitation over the region, primarily driven by subtropical jet stream dynamics and upper-level trough over the WH. The EPEs in cluster-3 are linked with positive phase of North Atlantic Oscillation, while weaker Tibetan anticyclonic circulation is observed in the cluster-4 compared to cluster-3.
How to cite: Deb, P., Bharati, P., and Hunt, K.: Synoptic and Large-Scale Drivers of Extreme Precipitation Events in the Western Himalaya, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19094, https://doi.org/10.5194/egusphere-egu25-19094, 2025.
Climatological and meteorological aspects of heatwaves (HWs) have been extensively studied in various parts of the world, as these extreme weather events have significant harmful effects on both humans and the environment. Several studies have examined HW climatology in Ukraine for specific historical periods using observational air temperature data. However, these results were obtained based on a relatively small number of meteorological stations.
In our study, we calculated HW climatology in Ukraine for both the current historical (1946–2020) and the projected (2020–2100) periods. For the historical period, we utilized the observation-based gridded dataset ClimUAd, which was recently developed for Ukraine. These gridded data are based on a comprehensive collection of instrumental meteorological measurements collected at 178 stations during 1946-2020 across the country. The dataset provides gridded daily time series of four essential climate variables: minimum, mean, and maximum surface air temperature, as well as atmospheric precipitation. The spatial resolution of ClimUAd is 0.1° × 0.1° in both longitude and latitude, enabling the analysis of HW climatology with fine spatial detail across Ukraine.
For the projected period, we applied a mini-statistical ensemble of climate simulations obtained with seven global climate models (GCMs) from the Coupled Model Intercomparison Project Phase 6. GCMs were selected for the ensemble based on two criteria: the use of the Gregorian calendar and a computational grid resolution no courser than 1.5o×1.5o. Our analysis incorporated climate projections obtained under two Shared Socioeconomic Pathways (SSP) scenarios: SSP2-4.5 and SSP5-8.5. Prior to calculating HW metrics, all climate projections of surface air temperature were bias-corrected using the quantile delta mapping method. In the bias-correction procedure, ClimUAd data were used along with historical climate simulations for the period 1985-2014.
For both the historical and projected periods, HWs were identified using daily maximum air temperature (TX) data. To detect HWs, we define this extreme weather phenomenon as an event when TX exceeds the 90-th percentile, calculated based on the WMO standard reference period of 1961-1990, for at least three consecutive days, allowing for a one-day gap. This approach is frequently used and widely recommended in studies as the most suitable for HW analysis with pure climatological purposes. The applied definition enables the identification of HWs throughout an entire year. To quantify HW peculiarities, we calculated four HW metrics on a yearly scale: HW number, HW frequency, HW duration, and HW amplitude. All HW calculations were performed using the heatwaveR package.
Our findings revealed a significant increase in all HW metrics during the historical period, with the most pronounced changes observed in the western part of Ukraine. In the projected period, the HW metrics continue to increase at a similar rate for both considered SSPs until approximately the mid-century. However, in the latter part of XXI, changes in HW climatology under SSP5-8.5 differ considerably from those under SSP2-4.5. The SSP5-8.5 scenario indicates that more than half of days in a year at the end of XXI could qualify as HWs.
This work has received funding through the MSCA4Ukraine project, funded by the European Union
How to cite: Skrynyk, O., Aguilar, E., Sidenko, V., and Skrynyk, O.: Heatwave climatology in Ukraine: current (1946-2020) and projected (2020-2100), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8369, https://doi.org/10.5194/egusphere-egu25-8369, 2025.
Posters virtual: Thu, 1 May, 14:00–15:45 | vPoster spot 5
EGU25-9608 | Posters virtual | VPS6
On the links between large-scale atmospheric circulation and extreme precipitation in the middle and lower Danube basinThu, 01 May, 14:00–15:45 (CEST) | vP5.4
The aim of this study was to find the connection between the large-scale atmospheric circulation in the winter season and the occurrence of extreme precipitation in the spring months at the regional scale. For the large-scale circulation, climate indices (GBOI and NAOI) associated with the Greenland-Balkan Oscillation and the well-known North Atlantic Oscillation were considered, and for the regional scale, certain representative stations for the middle and lower Danube basins were considered. The tests were carried out for a 120-year interval (1901-2020), by applying the extreme value theory (EVT). The modelling of maximum precipitation was carried out through the generalized extreme value (GEV) distribution. In order to see the impact of the large-scale circulation, the results obtained by incorporating NAOI as covariate into the location parameter of GEV distribution, were compared with the results obtained considering GBOI as covariate. For extreme precipitation in the lower basin area, the influence of GBOI is much more significant than that of NAOI, while for the middle basin area, the differences between the two indices are not so significant.
How to cite: Mares, I., Dobrica, V., Mares, C., and Demetrescu, C.: On the links between large-scale atmospheric circulation and extreme precipitation in the middle and lower Danube basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9608, https://doi.org/10.5194/egusphere-egu25-9608, 2025.
