Coupling hotter and drier extremes under elevating air temperature over eastern monsoon China

Summer hot and dry extremes (defined as high air temperature and low atmospheric humidity) in monsoon (climatologically high-humidity) region, may cause severe disasters, such as flash droughts. However, it remains unclear whether hot (dry) extremes are amplified on dry (hot) days to warming temperature. Here, taking eastern monsoon China (EMC) as a typical monsoon region, we find a fastest positive (negative) response of air temperature (atmospheric humidity) on driest (hottest) days to per unit warming, indicating amplified warming (drying) of hot (dry) extremes on dry (hot) days (i.e. coupling hotter and drier extremes) especially in southern EMC.  The southern EMC is also a hotspot where the coupling of hot and dry extremes has become significantly stronger during the past six decades. The increasing hot-dry extremes in southern EMC is associated with anomalies in large-scale environmental conditions, such as reduced total cloud cover, abnormal anticyclone in upper atmosphere, intense descending motion, and strong moisture divergence over this region. Land-atmosphere feedbacks play another important role in enhancing the hot-dry coupling via increasing land surface dryness (described as decreasing evaporation fraction). The decreasing evaporation fraction is associated with drying surface soil moisture which is controlled by decreases in pre-summer 1-m soil moisture and summer-mean precipitation. Given hot extremes (atmospheric humidity) are (is) projected to increase (decrease) in the future, it is very likely to witness more hot-dry days in monsoon regions and associated disasters, which should be mitigated by adopting adaptive measures.