Causes and Predictability of the 2021 Spring Southwestern China Severe Drought

In the spring of 2021, southwestern China (SWC) experienced extreme drought, accompanied by the highest seasonal-mean temperature record since 1961. This drought event occurred in the decaying phase of a La Nina event with negative geopotential height anomalies over the Philippine Sea, which is distinct from the historical perspective. Historically, spring drought over SWC is often linked to El Nino and strong western North Pacific subtropical high. Here, we show that the extreme drought in the spring of 2021 may be mainly driven by the atmospheric internal variability and amplified by the warming trend. Specifically, the evaporation increase due to the high temperature accounts for about 30% of drought severity, with the contributions of its linear trend portion being nearly 20% and the interannual variability portion being about 10%. Since the sea surface temperature forcing from the tropical central and eastern Pacific played a minor role in the occurrence of drought, it is a challenge for a climate model to capture the 2021 SWC drought beyond one-month lead times.

Automated summary

In the spring of 2021, southwestern China experienced extreme drought and high temperatures. Unlike historical events, this drought was mainly caused by atmospheric internal variability and amplified by climate warming trends, rather than El Nino. Evaporation increase accounted for 30% of the drought severity, with 20% contributed by its linear trend and 10% by interannual variability. The sea surface temperature forcing played a minor role in the occurrence of drought, making it difficult for climate models to predict the 2021 drought in southwestern China beyond one-month lead times.