The Yangtze River Valley (YRV) experienced an unprecedented heatwave in midsummer of 2022, but the detailed physical processes involved in the influence of anomalous large-scale atmospheric circulation on the heatwave remain unknown. Here, we show that the positive meridional gradient of anomalous atmospheric moisture at the middle-lower troposphere and associated extreme dry air advection over the YRV are key prerequisites for the formation of the 2022 YRV heatwave. The 2022 YRV heatwave is dominated by the interannual variability, which contributes 72.7% to the total temperature anomalies. Diagnosis of the surface heat budget equation indicates that the surface cloud radiative forcing is the most important process in driving the 2022 YRV heatwave, which is dominated by the positive surface short-wave cloud radiative forcing associated with the suppressed precipitation and the middle-low clouds. The suppressed precipitation is induced by the vertical dynamical processes of anomalous moisture advection caused by the anomalous descending flows over the YRV, which are driven by the negative advection of anomalous latent heat energy by climatological meridional wind (anomalous dry air advection) according to the atmospheric moist static energy equation. Simulations from the Lagrangian model FLEXPART further indicate that the moisture anomaly over the north of YRV is mainly originated from the surface evaporation in the YRV, implying that there is a positive land-air feedback during the life cycle of the YRV heatwave. Our study adds a perspective to the existing mechanism analyses of the 2022 YRV heatwave to serve accurate climate prediction and adaptation planning.

Southeast Asian monsoon region is regularly stricken by drought, but less attention is paid due to its slow-onset and less visual impact. This study investigated the observed drought changes over Southeast Asian monsoon region and impacts of anthropogenic forcing using the Coupled Model Intercomparison Project phase 6 (CMIP6) models. We revealed an increasing drought risk for 1951-2018 due to more frequent and wide-spread droughts. The influence of anthropogenic forcing is successfully detected, which has increased the likelihood of the extreme droughts in historical simulation by reducing precipitation and enhancing evapotranspiration. The time of emergence of anthropogenic forcing in extreme drought occurrence and affected area occurs around the 1960s. The future projected severe and extreme drought risks are still beyond natural only forced changes under all scenarios. Our findings demonstrate a robust impact of anthropogenic forcing on drought risk over Southeast Asia, and highlight the importance of future pathway choice.

Drylands face more threat from droughts under global warming. It remains insufficient in quantifying the roles of potential evapotranpiration (PET) and precipitation (P) to drought changes in a warming climate. Thus, we quantified the relative contributions of PET and P and projected their future changes across global drylands under four scenarios from Phase Six of the Coupled Model Intercomparison Project (CMIP6) models. In the 21st century, the multimodel medians of hydroclimatic fields indicate relatively consistent trend patterns, showing a drying over most of global drylands except for East Asia, Middle East, Sahel and South Asia drylands. The standardized precipitation evapotranspiration index (SPEI) presents a robust and ubiquitous drying with scenario-dependent magnitudes. The fractional contributions of PET and P to the present-day drought changes are estimated to be approximately equal (~50%). For the near- and mid-term projections, PET (P) contributes ~58% (42%) and ~61% (~39%), respectively. In the long-term, the fractional contribution of PET (P) reaches ~65% (~35%), ~72% (28%), ~80% (~20%), ~85% (~15%) under four different scenarios, respectively. Furthermore, PET contributes more significantly in the North Hemisphere than in the South Hemisphere, particularly over the Mediterranean, central and East Asian drylands. Drought conditions tend to be relatively stable under low scenarios (SSP1-2.6 and SSP2-4.5), while exacerbate continuously under high scenarios (SSP3-7.0 and SSP5-8.5). By the end of 21st century, severe droughts like the present-day 1-in-20-yr events are estimated to become fairly common across global drylands. These results provide further understanding for making policy and adaption strategies for drylands.