Recent land and marine heatwaves, extreme precipitation events and even monthly global mean temperature anomalies shattered previous observed records by large margins and reached intensities that many would have conceived impossible based on observations so far.

Here, I first demonstrate how in recent decades the frequency of such record-breaking and record-shattering extremes strongly deviates from expectations in a stationary climate and demonstrate how the current high rate of forced warming contributes to the current high occurrence record-shattering extremes. I further identify and discuss the extremes of the last two decades with the highest record margins.

Furthermore, I review different ways of estimating the probability and potential intensity of future record-shattering extremes. Different approaches including statistical approaches, such as Statistical Weather Generators or the use of Generalized Extreme Value distributions with process-based covariates as well as climate model-based approaches such as initialized hindcasts, single-model initial condition large ensembles and ensemble boosting have been proposed to estimate the potential intensity of future record-shattering extremes. I review the strengths and weaknesses of these approaches and argue that combining different lines of evidence is crucial to increase confidence in such estimates.

Finally, I will discuss how some of these methods also reveal how physical mechanisms differ between very extreme events and more moderate ones, and how they help to evaluate potential process-based constraints to upper bounds of the intensity of future record-shattering extremes.

How to cite: Fischer, E.: Understanding and quantifying recent and potential future record-shattering extremes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8077, https://doi.org/10.5194/egusphere-egu24-8077, 2024.

Containing elevated topography, the Tibetan Plateau (TP) has significant thermodynamic effects for regional weather and climate change, where understanding energy and water exchange process (EWEP) is an important prerequisite. However, estimation of the exact spatiotemporal variability of the land-atmosphere energy and water exchange over heterogeneous landscape of the TP remains a big challenge for scientific community. Focused on the above scientific question, a series of atmospheric scientific experiments and research programs have been conducted since the 1960s, quantitatively evaluating both the spatial distribution and the multi-timescale variation of EWEP via observation, remote sensing, and numerical simulation. Based on the three main approaches, the major advances on EWEP over the past 30 years are systematically summarized in this work. All these results advanced the understanding of different aspects of EWEP over the TP by using in situ measurements, multisource satellite data and numerical modeling. Future studies are recommended to focus on the optimization of the current three-dimensional comprehensive observation system, the development of advanced parameterization schemes and the investigation of EWEP on weather and climate changes over the TP and surrounding regions.

How to cite: Ma, Y.: The energy and water exchange and its effect on the weather and climate over the Tibetan Plateau and surrounding regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3834, https://doi.org/10.5194/egusphere-egu24-3834, 2024.

Daytime-nighttime compound heat waves (HWs) (i.e. concurrent occurrence of HWs both in daytime and nighttime) were documented to amplify the damages of high temperatures during daytime or nighttime. Nevertheless, the future change in compound HWs remains an open issue. This research presents the projected changes in compound HWs and associated population exposure in China under the shared socioeconomic pathway (SSP)2-4.5 and SSP5-8.5 scenarios based on the Coupled Model Intercomparison Project phase 6 simulations. The results generally indicate an aggravated risk of compound HWs in China in the future under warmer scenarios. Compound HWs in China are projected to increase significantly toward the end of the 21st century, with larger increase under SSP5-8.5 than that under SSP2-4.5. The greatest changes occur in northwestern China and southern China. Compared with the daytime HWs (i.e. occurring only in daytime) or nighttime HWs (i.e. occurring only in nighttime), the projected increase in compound HWs is the greatest. Accordingly, the proportion of compound HWs to the total HW events tends to increase and that of daytime HWs tends to decrease toward the end of the 21st century. Due to substantial increases in compound HWs, the population exposure to compound HWs will increase significantly across the entire country. The projected increase of nationally averaged population exposure is 12.2-fold (7.9-fold) of the current in the mid-century (2046–2065) and further enhances to 16.3-fold (12.4-fold) in the end-century (2081–2100) under SSP5-8.5 (SSP2-4.5). The largest increases are distributed in western China and southern China. These findings raise the necessity and urgency for policy-makers and the public to develop measurements to address compound HW risks.

How to cite: Xie, W.: Substantial increase in daytime-nighttime compound heat waves and associated population exposure in China , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2422, https://doi.org/10.5194/egusphere-egu24-2422, 2024.

How to cite: Luo, B., Xiao, C., Luo, D., Dai, A., Simmonds, I., and Wu, L.: Origins of Barents-Kara sea-ice interannual variability modulated by the Atlantic pathway of ENSO, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1703, https://doi.org/10.5194/egusphere-egu24-1703, 2024.

Extreme seasons (climate extremes) are of particular relevance to impacts, as they can produce accumulated effects on, for example, surface melt of ice shelves and penguin breeding. There is a gap in knowledge on how extreme seasons may change over Antarctica and the Southern Ocean under future climate forcing scenarios, with Antarctica not included in the IPCC AR6 WG1 Chapter 11 on extremes. In this presentation, available large ensemble datasets in the Coupled Model Intercomparison Phase 6 (CMIP6) archive were used to provide the first multi-variate overview of the evolution of extreme seasons over Antarctica and the Southern Ocean during the 20^th and 21^st centuries, with projections following medium-to-high radiative forcing scenarios (SSP2-4.5 and SSP3-7.0 forcing experiments). The variables assessed were near-surface temperature, surface precipitation rate and near-surface westerly wind. The results show significant differences between simulated changes in background mean climate and changes in low (10^th percentile) and high (90^th percentile) extreme seasons. Regional winter warming is most pronounced for cold extremes, particularly over or near to areas of climatological 20^th century sea ice cover. In summer there are more pronounced increases in high extremes in precipitation and westerly wind during the ozone hole formation period (late 20^th century) affecting coastal regions and in particular the Antarctic Peninsula. At sub-polar latitudes (between 50 and 60 degrees South) there is an approximately 20% reduction in the range of summer season wind extremes. Potential mechanisms/processes responsible for these differences will be discussed.

How to cite: Bracegirdle, T., Caton Harrison, T., Holmes, C., Lu, H., Martineau, P., and Phillips, T.: Antarctic extreme seasons under 20th and 21st century climate change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15936, https://doi.org/10.5194/egusphere-egu24-15936, 2024.

The majority of soil loss was triggered by several extreme rainfall events. Global warming may lead to an intensification of the surface water cycle and an increase in the probability and intensity of extreme rainfall events. An in-depth analysis of extreme event rainfall erosivity is valuable to help decision-makers take targeted measures to deal with future risks to soil and water resources protection. Cumulative rainfall erosivity from extreme events and characteristics of the 20- largest extreme events were analyzed based on the hourly rainfall data of 2420 meteorological stations over mainland China from 1951 to 2020. We sorted events at each site in descending order and calculated the percentage of events with accumulated erosivity (rainfall) accounting for 80% of total erosivity (rainfall) to all events (D80). Analysis on D80 shows 57% and 27% of extreme events of total events contribute 80% of rainfall and rainfall erosivity averaged over China, respectively, which indicates the impact of extreme erosivity is more predominant than that of extreme rainfall. The northern rock soil region (NR) and southwestern rock mountain region (SWR) were two regions with the least D80 among the six water erosion regions, which indicated fewer extreme events contributed to 80% of rainfall or rainfall erosivity compared with the other regions. D50 varies from 3% to 25% with a mean of 8% averaged over mainland China, which is more extreme than Europe (from 1% to 24 with a mean of 11%). TOP20_erosivity for extreme events with a descending order of event erosivity accumulates 29% of total erosivity, which is compared with 12% of TOP20_erosive for extreme events with a descending order of event rainfall. The average amount, duration and peak hourly intensity for TOP20_erosivity extreme events in summer are 14.6 mm,2.8 h, and 5.0 mm/h, respectively, while those for TOP20_rainfall are 16.5 mm, 4.4 h, and 3.4 mm/h, respectively, which indicate extreme erosive events are with a larger amount, shorter duration and greater peak intensity, comparing with extreme rainfall events. We further compared the synchronicity of the month with the maximum occurring frequency of extreme erosivity events and extreme rainfall events and found there are 33% of stations with not the same month. There were 19% of stations with the maximum month for erosive events preceding that for rainfall events and 14% of stations with the maximum month for erosive events lag behind rainfall events. 

How to cite: Chen, L., Xiao, Y., Yin, S., Wang, W., Strohmeier, S., Vásquez, C., Klik, A., and Strauß, P.: In-depth analysis of extreme event of rainfall erosivity over mainland China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19636, https://doi.org/10.5194/egusphere-egu24-19636, 2024.

Mei-yu is an important weather phenomenon in the middle-lower Yangtze River valley (YRV) region. For instance, in 2020, extreme precipitation events frequently occurred in the YRV region during the Mei-yu period, which caused flood and resulted in over 200 deaths/missing persons and over 170 billion CNY of direct economic losses. Whereas in 2022, persistent high temperature and drought events occurred in the YRV region, which greatly affected the agriculture, hydropower, and human health in the YRV region. These extreme events during the Mei-yu period have brought severe challenges to the government for combating climate change.

This study investigates the changes in the characteristics of Mei-yu under global warming and the potential reasons based on observation and reanalysis data during 1961–2022. It is found that the number of days without rainfall (NDWOR), intensity of rainfall event, and frequency and intensity of extreme precipitation events (EPE) in the YRV region have increased significantly during the Mei-yu period (June 15–July 10) over past decades. These trends indicate that the weather during the Mei-yu period is becoming more unstable and extreme under global warming. Particularly, the increasing trends in intensity of rainfall events and EPE (NDWOR) account for a relatively large (small) portion of the variability of corresponding variables, suggesting that the increased rainfall intensity is a key feature in the response of Mei-yu to climate change.

The increasing trend of NDWOR during Mei-yu is attributed to decreased relative humidity. According to the Clausius-Clapeyron equation, the saturation specific humidity (qs) would dramatically increase as the global warming continues, at an increasing rate of approximately 7% per℃ rise in temperature. As qs increases more dramatically than q under global warming, the RH is decreased, which may lead to more days without rainfall during the Mei-yu period.

The increased intensity of rainfall event, and frequency and intensity of EPE may be correspond to the thermodynamic and dynamic effects in the YRV region during the Mei-yu period. Through analyzing the regional rainfall events in the relatively cold period of 1961–1980 and in the relatively warm period of 2001–2022, it is found that the transient southerly water vapor transport, water vapor convergence and enhanced convection in the troposphere associated with the regional rainfall events in the YRV region during the relatively warm period are notably larger than that during relatively cold period during the Mei-yu period.

Furthermore, the response of Mei-yu to 2℃ of global warming with respect to pre-industrial climate is analyzed using CMIP6 models. The results suggest that the NDWOR, intensity of rainfall events, and frequency of EPE will increase in the YRV region during the Mei-yu period under the 2℃ warming scenario, which imply a more challenging climate risk management in the future.

How to cite: Sun, B.: How Does Mei-yu Respond to Climate Change?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2283, https://doi.org/10.5194/egusphere-egu24-2283, 2024.

Reanalysis and observational data are used to identify the precursors of summertime
heatwaves over the Eastern Mediterranean over the historical period. After compiling
a list of heatwaves using objective criteria, we identify robust precursors present 7 to 10
days before the onset of the heatwave, longer than the typical horizon for trustworthy
weather forecasts. If these precursors are present, there is a significant warming over
the Eastern Mediterranean over the following 10 days that then persists for weeks
after. These precursors include a weakened Indian monsoon, warm West/Central
Mediterranean Sea surface temperatures, and a low disturbance from the west. Further,
horizontal temperature advection is the proximate cause of the heatwave in the days
before the extreme, and in particular a weakening of the Etesian winds that would
otherwise advect relatively cool maritime air inland accounts for around half of the
warming. There is a clear tendency for more heat extremes in recent years. These
results have implications for the forecasting of summer heatwaves in the Eastern
Mediterranean, and the framework developed here can be applied in other regions as
well.

How to cite: Garfinkel, C., Rostkier-Edelstein, D., Morin, E., Hochman, A., Schwartz, C., and Nirel, R.: Precursors of summer heatwaves in the Eastern Mediterranean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6615, https://doi.org/10.5194/egusphere-egu24-6615, 2024.

Heavy Meiyu-Baiu rainfall occurred over central-east China and Japan in June-July 2020. This study analyzes observational and reanalysis data and performs atmospheric model simulations to investigate its causes. It is found that low Arctic sea ice cover (SIC) in late spring-early summer of 2020 along the Siberian coast was an important factor. The low SIC caused local warming and high pressure, resulted in excessive atmospheric blockings over East Siberia, which caused cold air outbreaks into the Meiyu-Baiu region, stopped the seasonal northward march of the Meiyu-Baiu front, and increased the thermal contrast across the front, leading to record-breaking rainfall in June-July 2020. Our results suggest that the 2020 extreme Meiyu-Baiu was partly caused by the low SIC around the Siberian coast through its impact on East Siberian blockings. Further analysis shows that Indian Ocean warming and the Arctic sea-ice loss has combined effect on the particularly heavy rainfall in July 2020.  Their effects are interdependent rather than additive. Strong IO warming is rarely observed alongside severe Arctic sea-ice loss before 2020 because of their discordant interannual variations. In the future, the combined effects of IO warming and Arctic sea-ice loss on the Meiyu-Baiu rainfall may become more pronounced as their long-term trends continue. 

How to cite: Chen, X., Wen, Z., and Dai, A.: Contributions of Arctic Sea-ice Loss and East Siberian Atmospheric Blocking to 2020 Record-breaking Meiyu-baiu Rainfall, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4868, https://doi.org/10.5194/egusphere-egu24-4868, 2024.

Extreme weather and climate events are the result of interaction of multiple scale anomalous signals. Solar activity presents a remarkable 11-year cycle, which is an important decadal background affecting the occurrence of extreme weather and climate events. A lot of study works show that the periodic variation of solar activity has a modulating effect on the ocean-atmosphere system. The decadal variation of major atmospheric and oceanic modes, such as ENSO, has a phase-locked relationship with the periodic variation of solar activity. A significant solar footprint can be found in the tropical Pacific and the North Atlantic. The analysis shows that the solar activity also modulates the regional temperature, precipitation and typhoon activity as well.

How to cite: Xiao, Z. and Zhao, L.: Impact of solar activity on extreme weather and climate events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2235, https://doi.org/10.5194/egusphere-egu24-2235, 2024.

This study aims to analyze variations in atmospheric moisture supply from major remote Brazilian hydrological basins during meteorological drought episodes in the La Plata Basin (LPB). The analyses were conducted for the period 1980-2018, using a Lagrangian diagnostic methodology that estimates the contribution of atmospheric moisture to the water balance in the region. The method relies on the Lagrangian model FLEXPART integrated with ERA-Interim reanalysis data. The technique calculates the difference between evaporation and precipitation by computing temporal variations in specific humidity of air parcels identified over the major Brazilian basins along their trajectories forward in time towards the LPB. During the analysis period, a total of 49 meteorological drought episodes were identified over the LPB through the time series of the monthly SPEI-1 (Standardized Precipitation-Evapotranspiration Index). Linear regression analysis indicates a relationship between variations in atmospheric moisture supply by air parcels traveling from several basins (Amazon, North Atlantic, and Tocantins) and the duration, severity and peak of drought episodes over LPB. This implies that more severe, longer, and higher peak dry episodes in the LPB were associated with a decrease in atmospheric moisture supply from the air parcels traveling from these basins. 

How to cite: Porfírio da Rocha, R., Drumond, A., de Oliveira, M., Stojanovic, M., and Nieto, R.: Climate variability in the atmospheric moisture supply during meteorological drought episodes over La Plata Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5904, https://doi.org/10.5194/egusphere-egu24-5904, 2024.

Despite the high confidence in the overall intensification of the hydrological cycle in response to global warming, future changes in the spatiotemporal distribution of extreme precipitation remain uncertain. We here explore how climate change affects the seasonality and timing of extreme precipitation, which potentially alters its impact on society, economy and ecosystems substantially. Extreme precipitation events are defined as an exceedance of the all-day 98th percentile of daily precipitation.

Most of the CMIP6 models capture the historical timing of extreme precipitation compared to the REGEN observational data. With climate change, we find distinct regional shifts in extreme precipitation across models. The most pronounced signal is a distinct shift of extreme precipitation from summer into the shoulder seasons, spring and autumn, or even into winter at latitudes between about 45°N and 75°N in Eurasia and northeast America.  These regions, which are climatologically characterized by extreme precipitation predominantly occurring during the summer, are projected to experience a strongly reduced fraction of extreme precipitation in summer during the second half of the 21^st century.

Preliminary synoptic analysis in individual models indicates a combined effect of limited moisture supply and weaker updrafts during the core summer extreme precipitation events. Further analysis is required to disentangle the relative role of thermodynamic and dynamic contribution to impact-relevant changes in seasonality of extreme precipitation.

How to cite: Zhu, D., Pieper, P., Pfahl, S., Fischer, E., and Knutti, R.: Future shifts in timing of regional extreme precipitation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11057, https://doi.org/10.5194/egusphere-egu24-11057, 2024.

Accurate sub-seasonal (2-8 weeks) prediction of monsoon precipitation is crucial for mitigating flood and heatwave disasters caused by intra-seasonal variability (ISV). However, current state-of-the-art sub-seasonal-to-seasonal (S2S) models have limited forecast skills beyond one week when predicting ISV events. Here, we find, regardless of models, that the prediction skills for ISV events depend on the propagation stability of events’ preceding signals. This allows us to identify opportunities and barriers (OBs) within S2S models, understanding what the models can and cannot achieve in ISV event prediction. Focusing on the complex East Asian summer monsoon (EASM), we discover that stable propagation of Eurasian and tropical atmospheric wave trains towards East Asia serves as an opportunity, providing skillful prediction up to 13 days ahead. However, the Tibetan Plateau barrier highlights the limitation of EASM predictability. Identifying these OBs will help us gain confidence in making accurate sub-seasonal prediction.

How to cite: Liu, F.: Identifying opportunities and barriers for skillful sub-seasonal prediction of East Asian summer monsoon precipitation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2659, https://doi.org/10.5194/egusphere-egu24-2659, 2024.

In recent decades, unprecedented heatwaves have resulted in substantial impacts on human health and their environment. Previously, heatwave trend analysis has largely focused on trends across global warming thresholds or on specific regions. Furthermore, a variety of diverse heatwave parameters has been applied across separate studies, hampering direct comparison. What is more, there has been limited information on how future projections of individual events compare to recent extreme heatwaves.

In our study, we define heatwaves as periods of at least three consecutive days where daily area-weighted mean temperature exceeds the regional 90^th percentile. We utilize a comprehensive analysis framework based on four heatwave parameters and additional sub-parameters where appropriate: (1) heatwave duration in days, (2) heatwave severity, an intensity index enabling interpreting excess heat relative to the regional climatology, (3) cumulative heat, and (4) percentage of locally affected area. The latter is an area-based parameter providing information on the exceedance of local (grid cell level) climatology thresholds during the course of an individual heatwave in percent of the respective region’s overall area. For parameters (2) and (4) we, moreover, investigate two sub-parameters, namely median and maximum values. The first sub-parameter refers to the median value of the entire heatwave, whereas the second indicates that this maximum value is being reached for at least one day during the event. This analysis framework greatly increases the ability for individual heatwave-based and regional intercomparison, and, furthermore, explores both regional as well as local scale trends, thereby providing critical human-impact-oriented information. In addition to daily output from multi-model ensembles from models taking part in the Coupled Model Intercomparison Project Phase 5 and 6 and large initial-condition ensembles (CanESM5 and ACCESS-ESM1-5), we employ our framework to 14 regional events observed during the period of 2010-2021 and analyzed based on Berkeley Earth and ERA5. This provides crucial insights into how future heatwaves compare to recent events.

Our results indicate that recently observed extreme heatwaves are dwarfed by projected 21^st century events. Moreover, without even moderate reduction in greenhouse gas emissions the probability of reoccurrence or exceedance of these recent extreme reference values is significantly increasing, and they are still plausible under aggressive emission reduction scenarios.

In conclusion, we can see that a lack of mitigation and adaptation measures could considerably increase human exposure to extreme heat. In particular as we found, depending on the scenario, significant increases in the percentage of locally affected area and the heatwave severity. Thus, these findings stress the necessity for substantial and ambitious mitigation efforts and for considering heatwaves well outside the lived experience for effective adaptation measures.

How to cite: Aglas-Leitner, P., Perkins-Kirkpatrick, S. E., and Stone, D.: Recent extreme heatwaves dwarfed by projected future events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10648, https://doi.org/10.5194/egusphere-egu24-10648, 2024.

Climate change adaptation and relevant policy-making need reliable projections of future climate. Methods based on multi-model ensemble are generally considered as the most efficient way to achieve the goal. However, their efficiency varies and inter-comparison is a challenging task, as they use a variety of target variables, geographic regions, time periods, or model pools. Here, we construct and use a consistent framework to evaluate the performance of five ensemble-processing methods, i.e., multimodel ensemble mean (MME), rank-based weighting (RANK), reliability ensemble averaging (REA), climate model weighting by independence and performance (ClimWIP), and Bayesian model averaging (BMA). We investigate the annual mean temperature (Tav) and total precipitation (Prcptot) changes (relative to 1995–2014) over China and its seven subregions at 1.5 and 2 °C warming levels (relative to pre-industrial). All ensemble-processing methods perform better than MME, and achieve generally consistent results in terms of median values. But they show different results in terms of inter-model spread, served as a measure of uncertainty, and signal-to-noise ratio (SNR). ClimWIP is the most optimal method with its good performance in simulating current climate and in providing credible future projections. The uncertainty, measured by the range of 10th–90th percentiles, is reduced by about 30% for Tav, and 15% for Prcptot in China, with a certain variation among subregions. Based on ClimWIP, and averaged over whole China under 1.5/2 °C global warming levels, Tav increases by about 1.1/1.8 °C (relative to 1995–2014), while Prcptot increases by about 5.4%/11.2%, respectively. Reliability of projections is found dependent on investigated regions and indices. The projection for Tav is credible across all regions, as its SNR is generally larger than 2, while the SNR is lower than 1 for Prcptot over most regions under 1.5 °C warming. The largest warming is found in northeastern China, with increase of 1.3 (0.6–1.7)/2.0 (1.4–2.6) °C(ensemble’s median and range of the 10th–90th percentiles) under 1.5/2 °C warming, followed by northern and northwestern China. The smallest but the most robust warming is in southwestern China, with values exceeding 0.9 (0.6–1.1)/1.5 (1.1–1.7) °C. The most robust projection and largest increase is achieved in northwestern China for Prcptot, with increase of 9.1%(–1.6–24.7%)/17.9% (0.5–36.4%) under 1.5/2 °C warming. Followed by northern China, where the increase is 6.0%(–2.6–17.8%)/11.8% (2.4–25.1%), respectively. The precipitation projection is of large uncertainty in southwestern China, even with uncertain sign of variation. For the additional half-degree warming, Tav increases more than 0.5 °C throughout China. Almost all regions witness an increase of Prcptot, with the largest increase in northwestern China.

How to cite: Jiang, Z., Zhu, H., Li, L., Li, W., Jiang, S., Zhou, P., Zhao, W., and Li, T.: Intercomparison of multi-model ensemble-processing strategies within a consistent framework for climate projection in China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2996, https://doi.org/10.5194/egusphere-egu24-2996, 2024.

In recent years, the eastern China and even the whole northern hemisphere have suffered from frequent extreme climate events in summer. For example, the extremely hot summer of 2018 over East Asia, the abnormal precipitation in eastern China in the midsummer of 2021, and the high summer temperature in the Northern hemisphere in 2022 August. These extreme climate events have brought severe challenges to human life, economic development and ecological environment. Revealing the physical mechanism of such events is of great significance for disaster prevention and mitigation and policy making.

In fact, atmospheric circulation anomalies play an important role in regulating extreme climate events on a regional scale. However, the existing research mainly focus on the influence of the horizontal vortex circulations processes such as blocking and wave train, but the effects of local vertical circulations, especially the interaction between the local vertical and horizontal circulations, are still lacking. To explore a dynamic approach that considers the actual atmospheric circulation as a whole, Hu et al. (2017,2018a, 2018b, 2020) proposed a novel method called the three-pattern decomposition of global atmospheric circulation (3P-DGAC). Unlike the traditional two-dimensional decomposition method, which ignores the effects of the horizontal motion of low-latitudes and the vertical motion of mid-high latitudes, this method considers the effects of mid-high latitude divergent circulation and low latitude vortex circulation on the actual atmospheric circulation, which is conducive to the study of the dynamics of the actual atmospheric circulation from the global perspective. Specifically, the 3P-DGAC extends Rossby wave at mid-latitudes, Hadley circulation and Walker circulation at low latitudes to the global scale, and argues that the actual atmospheric circulation can be understood as the sum of the superposition of the horizontal vortex circulation, the meridional and zonal circulation. Thus, the 3P-DGAC provides a suitable tool for studying the dynamics of three-dimensional structure of local atmospheric circulation.

Using the 3P-DGAC method, we have studied the dynamics of the extreme climate events that have occurred in recent years and revealed the corresponding physical mechanisms, the findings suggest that local vertical circulations play a non-negligible role in extreme climate events. This study is expected to provide a reliable theoretical reference for the prediction of extreme climate events.

How to cite: Peng, J. and Hu, S.: Dynamic study of extreme climate events based on the three-pattern decomposition of global atmospheric circulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5067, https://doi.org/10.5194/egusphere-egu24-5067, 2024.

A fundamental characteristic of extreme precipitation events (EPEs) is the horizontal scale of the associated vertical motions, called “extreme ascent.” This horizontal scale can influence the intensity of an EPE through its effect on the temporal and spatial scales of an EPE as well as its effect on the strength of convective feedbacks. Thus, to have confidence in future projections of extreme precipitation, the horizontal scale of extreme ascent and EPEs in GCMs should be evaluated. Analyzing daily output from 27 models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6), including 13 models participating in the High Resolution MIP (HighResMIP), we computed the horizontal scales of EPEs and extreme ascent for annual maximum EPEs during 1981-2000. We found that the horizontal scale of both EPEs and extreme ascent are resolution dependent, and the horizontal scales decrease as the horizontal model resolution increases. Further analysis reveals that this resolution-dependence is due to the fact that the precipitation during the EPEs is almost entirely resolved (rather than parameterized) precipitation. However, the EPEs are not simply grid-box storms and analysis of the horizontal scales of geopotential anomalies suggests that the large-scale dynamics in GCMs is not resolution dependent. Thus, the dominance of resolved precipitation during EPEs is more likely due to convection on the model grid or formation of strong fronts, and additional work is needed to explore these possibilities further and find a solution for the resolution dependence. This work is currently undergoing revision for consideration by Journal of Geophysical Research-Atmospheres.

How to cite: Tandon, N. and Ali, A.: Influence of horizontal model resolution on the horizontal scale of extreme precipitation events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20716, https://doi.org/10.5194/egusphere-egu24-20716, 2024.

The far-reaching impacts of humid heat extremes on public health and ecosystems underscore a necessity for a comprehensive investigation. South Asia is a global hotspot where humid heat reaches some of  the highest levels globally in a densely populated region, and climatologically highly interesting since temperatures typically peak in the pre-monsoon period, and humid heat only several weeks later during the monsoon period. This study examines the historical trends in humid heat extremes, and their underlying drivers and mechanisms during the pre-monsoon (Mar-May) and monsoon (June-September) seasons over South Asia. Our findings reveal a notable surge in the warming trends of humid heat extremes since 2000, exhibiting a rate exceeding twice that of observed long-term trends since 1950 in the monsoon season across South Asia. During the pre-monsoon season, short-term trends (trends since 2000) exhibit diverse regional patterns, indicating cooler heat extremes in western South Asia, while the rest of the region experiences increasing trends in heat extremes. This contrasts with the consistent and regionally coherent long-term warming trends in humid extremes since 1950 across South Asia. 

We further show that the seasonal evolution of daily maximum wet-bulb temperature in South Asia is closely linked with humidity levels, indicating that the occurrence of high humidity events governs the timing of humid heat extremes. During the monsoon season, higher humidity in Southern and Central South Asia occurs ~2 weeks earlier since 2000 compared to the climatological period (1950-1979). This elevated humidity aligns with several ℃ higher temperatures occurring earlier in the season, intensifying humid heat extremes. In western South Asia, changing humidity trends notably impact humid heat extremes: rising trends intensify them during the monsoon season, while declining trends cool pre-monsoon extremes. Further, we show that precipitation variability modulates humidity levels and, thereby, the intensity of humid heat extremes over western South Asia. Moreover, our study notes a significant increase in the duration of monsoon season humid heat extremes, expanding from ~2 days in the 1950s to several weeks in recent decades across South Asia. This prolonged and sustained occurrence is predominantly associated with consistent and high humidity levels. The emergence of such strong trends emphasizes the need to expedite adaptation and mitigation measures to align with the substantial escalation in humid heat intensity and duration.

How to cite: Singh, J., Fischer, E., Singh, D., and Sippel, S.: Emergence of strong trends in humid heat intensity and duration in recent decades over South Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17194, https://doi.org/10.5194/egusphere-egu24-17194, 2024.