Causes of the severe drought in Southwest China during the summer of 2022

Abstract

In summer 2022, Southwest China (SWC) suffered its worst drought since 1980, with a rainfall deficit and an extremely high temperature anomaly. This had a severely harmful effect on agricultural production, water resources, and hydroelectric supply over SWC. Both a less-than-normal water vapor supply and warmer-than-normal temperature contribute to the precipitation decrease associated with drought. Using the observed station data from the China Meteorological Administration and the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA5) data, our results show that the 2022 summer drought over SWC was caused by both the less-than-normal water vapor supply and warmer-than-normal temperature, and the warmer temperature played a more important role, unlike in previous droughts. The warmer air temperature for the 2022 summer induced record-breaking potential evapotranspiration (PET) over SWC, reducing surface water and drying out soils. Meanwhile, the warmer air temperature made it difficult for water vapor to reach saturation, resulting in a decrease in precipitation over the whole of SWC. We found that such anomalous water vapor supply and temperature were closely related to the South Asian high (SAH) during summer 2022. The SAH was stronger and covered a larger area than during other summer SWC droughts since 1980. The anomalous 2022 summer SAH inhibited the water vapor transport from the tropical Indian Ocean to SWC and further caused a significant warming temperature anomaly by regulating the thickness of the layer between isobaric surfaces, which contributed to the record-breaking summer drought over SWC. Our study highlights the vital role played by warmer temperatures in the 2022 summer drought. Considering that the warming air temperature under greenhouse-gas forcing may cause more droughts like that in 2022 in the future, the 2022 drought may yield useful information that will provide insight into future droughts and raise awareness of the impact of temperature on extreme climate events.