Attribution analysis of the persistent and extreme drought in southwest China during 2022-2023

Southwest China experienced a severe drought during winter 2022-spring 2023. This drought mainly struck Yunnan Province and surrounding regions (21 degrees-30 degrees N, 97 degrees-106 degrees E), with precipitation deficit lasting for about 8 months from Oct 2022 to May 2023. The area-mean precipitation and surface soil moisture in the study region during the drought were both the lowest recorded for the same period since 1950. The Standardized Precipitation Evapotranspiration Index (SPEI) also reached its lowest level since 1950 at -2.76. Quantitative analysis shows that precipitation deficit and potential evapotranspiration (PET) increase contributed 71.36%, and 28.64% to the SPEI, respectively. Of the raw contribution of PET, 7.05% can in turn be attributed to the changes in precipitation. Using data from the CMIP6 Detection and Attribution Model Intercomparison Project (DAMIP), we found that anthropogenic forcing increased the likelihood of a PET anomaly such as the one during the drought by about 133 times, with a fraction of attributable risk (FAR) of 0.99 [0.98, 1.00]. For the precipitation anomaly, we obtained a FAR of 0.26 [-1.12, 0.70], suggesting that anthropogenic forcings may have little impact. The extreme drought also increased the risk of fires, with the Fire Weather Index reaching its second-highest value since 1950 and abnormally high burned areas observed by satellites.