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The standardized precipitation evapotranspiration index (SPEI) is computed and compared in China using reference evapotranspiration calculated using the Thornthwaite (TH) approach and the Penman–Monteith (PM) equation. The analysis reveals that SPEI_PM outperforms the SPEI_TH with regard to drought monitoring during the period 1961–2012 over China, especially in arid regions of China. Furthermore, the SPEI_PM also performs better with regard to observed variations in soil moisture and streamflow in China. Thus, changes in drought characteristics over China are detected on the basis of variations in the SPEI_PM. The results indicate that droughts over China exhibit pronounced decadal variations over the past 50 yr, with more frequent and severe droughts occurring before the 1980s and in the 2000s compared with the 1980s and 1990s. Since the late 1990s, droughts have become more frequent and severe across China, especially in some regions of northern China. Concurrently, consecutive drought events have also increased across China. This suggests that dry conditions in China have been enhanced in recent years. Further analyses illustrate that the temperature and precipitation anomalies exhibit different roles in detecting droughts across China, which is primarily due to the magnitude of their variations and different climate variability. Considering temperature and precipitation perturbations, droughts exhibit relatively larger responses to temperature fluctuations in northern China and relatively larger responses to precipitation anomalies in southern China.

Drought, one of the major natural disasters in China, generally causes the largest socioeconomic loss each year and also has severe human health impacts. It is thus crucial to assess the changes in droughts in this region under different climate change scenarios. This study examines the impacts of stabilized 1.5 °C and 2.0 °C warming at the end of the 21st century on drought events in China by using a set of coupled Earth system model low-warming simulations. If warming is limited to 1.5 °C or 2.0 °C, these simulations suggest that droughts will become more frequent and more intense compared to the present day, particularly over the northern regions of China. In comparison to the 1.5 °C warmer future, the 0.5 °C additional warming in the 2.0 °C warmer future will account for approximately 9% of the increase in the drought occurrence in China and approximately 8% of extreme droughts, while there are relatively small responses for moderate and severe droughts. Consequently, the additional warming would lead to significantly higher drought impacts, and the population exposure to the extreme droughts is projected to increase by approximately 17%, although the exposure to moderate droughts decreases. Therefore, our results suggest that the mitigation of anthropogenic warming by 0.5 °C to achieve the 1.5 °C warmer climate instead of the 2.0 °C climate may have benefits for future drought risks and impacts.

The social losses associated with extreme humid‐heat events (EHHE) increased sharply in recent decades. This study has explored the changing relationship between EHHE in eastern China and tropical sea surface temperature (SST) anomalies. Results show that the monopolar mode of EHHE is significantly associated with spring SST anomalies in Northwest Pacific (NWP) before the mid‐1990s, which can impact humid‐heat conditions in eastern China through an atmospheric meridional overturning circulation extending from NWP to eastern China. Then, the associated eastward shift of convection center after the mid‐1990s weakens connection between NWP SST anomalies and the monopolar mode. Further analysis reveals that the weakened Kelvin waves, induced by persistent SST anomalies from spring in tropical Indian Ocean after the mid‐1990s, cause the westward‐shifted anomalous convection in western Pacific, and then reinforce formation of the dipolar mode via exciting zonal wave trains. Numerical simulations via linear baroclinic model further validate atmospheric response to displacement of diabatic forcings. Plain Language Summary Extreme humid‐heat events, accompanied by abnormally high temperatures and humidity, exacerbate harmful impacts on society and human health. Based on dynamic statistical analysis, we discovered a significant shift in the relationship between summer EHHE and spring tropical SST anomalies around the mid‐1990s. Before then, EHHE in eastern China is closely tied to spring SST anomalies in the Northwest Pacific (NWP). Spring NWP SST anomalies may persist to summer and influence heat and moisture conditions in eastern China through an atmospheric meridional overturning circulation that extends from NWP to eastern China. However, the shifting position of circulation weakens the NWP‐EHHE connection after the mid‐1990s. Disparities in Kelvin waves induced by persistent Indian Ocean SST anomalies from spring lead to distinct positions of convective activity anomalies in the western Pacific. Post‐mid‐1990s, westward‐shifted anomalous convection influences eastern China's atmospheric circulation, reinforcing the dipolar EHHE mode. These findings enhance understanding and prediction of summer EHHE in eastern China. Key Points The link between summer extreme humid‐heat events (EHHE) and tropical sea surface temperature (SST) shifted notably by the mid‐1990s The eastward convection shift weakens the link between Northwest Pacific SST and the monopolar EHHE mode The weakened Kelvin waves induced by tropical Indian Ocean SST reinforce the dipolar EHHE mode

In this study, the water vapor sources for the precipitation processes in southeastern China (SECN) during 1981–2010 were investigated using atmospheric reanalysis data. We also studied the factors influencing the summer atmospheric moisture over SECN. These two issues are all closely related to the climate signals recorded in stalagmites recovered from caves in SECN. Result supports that the atmospheric water vapor over SECN during the whole summer time is primarily transported from the Indian Ocean. However, the vertically integrated water vapor content throughout the year in SECN has two main sources: the Indian Ocean and the tropical western Pacific. In addition, the water vapor transport for the precipitation processes in SECN has complex vertical structure. At approximately 700 hPa to 500 hPa, part of the water vapor for the precipitation in SECN comes from the Arab‐Caspian region. Finally, the water vapor content over SECN is regulated primarily by both the Indian and East Asian monsoons. Further analysis indicated that the variability of the East Asian summer monsoon is substantially regulated by the western Pacific subtropical high, the Eurasia–Atlantic thermal conditions, as well as the large‐scale Eurasia‐Atlantic atmospheric circulation. Therefore, the SECN Cave proxies can record the signals from faraway middle and high latitude Eurasia‐Atlantic climate, besides the regional East Asian monsoon and remote Indian monsoon. Key Points Moisture in southeastern China has multiple sources including Indian and Pacific Both Indian and East Asian monsoon can affect the moisture in southeastern China Southeastern China caves proxies can indicate East Asian and Indian monsoon

Precipitation extremes and associated hazards often cause agricultural losses and infrastructure damage and even exert negative impacts on human health. It is thus crucial to assess future changes in precipitation extremes and exposure under future warming scenarios to improve the mitigation of climate change. On the basis of Coupled Model Intercomparison Project phase 6 simulations, we find that occurring probabilities of precipitation extremes that exceed the 99th percentile threshold are projected to increase over global lands in the coming century, especially under the no‐mitigation scenario of SSP5‐8.5. Under this scenario, by the end of this century, occurrences of aggregations of precipitation extremes over global lands are expected to increase by approximately 1.8 times. Increases are also expected even if early mitigation is conducted via SSP1‐2.6. Accordingly, global aggregate exposure would increase by at least 50% in the future under SSP5‐8.5. Changes in precipitation extremes will exert a substantial influence on population exposure, of which contribution will be up to 46% under SSP5‐8.5 by the end of this century. The future maximum centers of exposure are concentrated over East Asia, South Asia, the Mediterranean basin, and eastern North America, as in the current state. However, the rapid increase in population over some parts of Africa plays a larger role than climate change and significantly increases the exposure in these regions. As a result, regions of Africa will become other high‐exposure global centers in the future. Climate change mitigation should be thus the key policy response to reduce population exposure in the future over most global regions. Plain Language Summary Risks of precipitation extremes and associated hazards have been reported to increase in the past decades around the world, which often caused agricultural losses, food shortages, infrastructure damage, and even human deaths. With further warming in the future, results from the Coupled Model Intercomparison Project phase 6 simulations show that the occurring risks of precipitation extremes are expected to obviously increase across the world over the coming century, especially under the no‐mitigation scenario of SSP5‐8.5. Correspondingly, there would be more population exposures to precipitation extremes across the world in the future, with the high exposure mainly centering over East Asia, South Asia, the Mediterranean basin, Eastern North America, and Africa. By the end of this century, the global aggregate exposure would increase by at least 50% with respect to the current climate under the SSP5‐8.5 scenario. Further analyses reveal that climate change exerts a substantial influence on the increased exposure though it varies from region and scenario. Climate change mitigation should be thus the key policy response to reduce population exposure to precipitation extremes in the future. Additionally, population growth also plays a great role in the increase of exposure over some regions, such as Africa. Key Points The occurring probabilities of precipitation extremes are projected to significantly increase over the coming century across the world The global aggregate exposure is expected to increase by at least 50% in the future if there is no mitigation to climate change Climate change exerts an increased influence on future exposure across the world and population growth also plays a great role in some regions

Changes in heat stress due to climate change affect living and working conditions. A wet-bulb temperature (TW) of 35 °C is identified as the upper physiological limit for human survivability. On the basis of Coupled Model Intercomparison Project phase 6 model simulations, our evaluations show that the daily maximum TW is expected to significantly intensify throughout China and is likely to exceed this critical threshold in some regions by the end of this century, especially under the high emission scenario of the shared socioeconomic pathway (SSP)5-8.5. The most dangerous hazard from extreme heat-humidity events is concentrated around the most densely populated regions of eastern China as well as the Sichuan basin. Under SSP5-8.5, the significant increase of extreme heat-humidity days with a daily maximum TW exceeding 35 °C results in a large fractional population of approximately 81% being exposed to these extremes in China by the end of this century. This is true for different future warming scenarios, and a population fraction of up to 51% would also be exposed to such extremes even if early mitigation was conducted via SSP1-2.6. Our findings in this study thus have significant implications to ongoing considerations for climate-change policy in China.

Precipitation extremes are among the most dangerous climate-related hazards, and these hazards often cause large socioeconomic losses and exert severe human health impacts each year. It is thus crucial to assess future exposure changes to precipitation extremes under different warming scenarios to improve the mitigation of climate change. Here, we project future exposure using a set of Coupled Earth System Model low-warming simulations and RCP8.5 large ensemble simulations. We find that the precipitation extremes are projected to significantly increase over the coming century under different future warming scenarios at both the global and regional levels. Compared to a 1.5 °C warmer climate, the 0.5 °C of additional warming under a 2.0 °C warmer future would increase the number of days of global aggregate precipitation extremes by approximately 3.6% by the end of this century. As a result, the global aggregate exposure is reported to increase by approximately 2.3% if the surface air temperature increases to 2.0 °C rather than 1.5 °C. An increase in exposure is also obvious for most regions across the world, and the largest increase in the future occurs over North Asia in response to the 0.5 °C of additional warming. Furthermore, exposure would increase more rapidly if the temperature increased following the RCP8.5 pathway. The exposure increase varies at the regional level, but in most cases, climate change shows more influential than that of the population; in addition, this influence does not depend on the population outcomes used here.

This study explores the model performance of the Coupled Model Intercomparison Project Phase 6 (CMIP6) in simulating precipitation extremes over the mid-high latitudes of Asia, as compared with predecessor models in the previous phase, CMIP5. Results show that the multimodel ensemble median generally outperforms the individual models in simulating the climate means of precipitation extremes. The CMIP6 models possess a relatively higher capability in this respect than the CMIP5 models. However, discrepancies also exist between models and observation, insofar as most of the simulated indices are positively biased to varying degrees. With respect to the temporal performance of indices, the majority are overestimated at most time points, along with large uncertainty. Therefore, the capacity to simulate the interannual variability needs to be further improved. Furthermore, pairwise and multimodel ensemble comparisons were performed for 12 models to evaluate the performance of individual models, revealing that most of the new-version models are better than their predecessors, albeit with some variance in the metrics amongst models and indices.

Snowfall is an important element of the climate system and generally has particularly large economic and human impacts. Simulations with climate models have indicated a decline in mean snowfall with warming in most regions. The response of intense snowfall events to a changing climate, however, is unclear. Thus, the degree which anthropogenic influence is responsible for intense snowfall change and how intense snowfall will respond to the changing climate in the future are addressed here using new simulations from Coupled Model Intercomparison Project phase 6 models. The results show that anthropogenic influences on changes in snowfall are detectable across the lands of the Northern Hemisphere and generally result in a decreasing trend in snowfall events. However, increased anthropogenic activity has increased intense snowfall occurrences over most parts of Asia, North America, and Greenland. With additional warming in the future, while the length of the snowy season will be shortened and the areas where snowfall occurs will be reduced, the occurrence probability of an intense snowfall event is projected to significantly increase with a level of high confidence over these regions by the end of this century. This suggests that these regions, including most parts of northern China, would suffer from more intense snowfall events in the future due to a continuous increase in anthropogenic influence.

This study investigates the characteristics of compound heat wave and drought events (CHDEs) across various subregions of China from 1961 to 2022 by utilizing a monthly probability-based index. The results uncover significant interregional and subseasonal variations. The trend analysis of CHDEs reveals statistically significant increases in most regions of China; however, there is no significant trend in the JiangHuai region throughout the entire summer season. The trends across regions exhibited subseasonal differences, especially in the eastern regions (Northeast China, North China, and South China (SC)). Furthermore, the occurrence of severe CHDEs (SCHDEs) in China has significantly increased in both frequency and extent since the 1990s. Southwest China and eastern Northwest China have witnessed the highest frequency of SCHDEs, while SC has remained relatively unaffected compared to other regions. The occurrences of SCHDE demonstrate a higher frequency occurred in June than in July and August, especially in the southern regions. The local driving factors are further explored. The incidence of CHDEs in eastern China is significantly influenced by anticyclonic circulation anomalies, which span from the upper to the lower troposphere. These anomalies are crucial in shaping the dynamic and moisture conditions necessary for CHDE formation. Their specific locations dictate the unique atmospheric conditions that lead to the regional characteristics of CHDEs across eastern China.