Change of summer drought over China during 1961-2020 based on standardized precipitation evapotranspiration index

With the aggravation of climate change, drought has become a more prominent extreme event with serious consequences. The selection of drought indices is crucial for accurate quantification and assessment of drought change and its impacts. In this study, we first evaluated the standardized precipitation evapotranspiration index (SPEI) at different time scales in terms of their applicability to reflect changes in summer drought over China through comparison with observation-based drought indices including soil moisture (SM) dataset. We found that precipitation and SM both exhibit a drying feature from northeastern China to southwestern China. At different time scales, the 1-month SPEI (SPEI-01) has the best performance in reflecting the changes of summer SM over China. Using SPEI-01, we examined the spatial pattern of change in drought intensity and frequency from 1961 to 2020 in China at a national scale and further compared drought change in regions with different aridities. Overall, China witnessed a wetting trend in the past 60 years. Arid and semiarid regions were featured with "dryer in the east and wetter in the west." A drying trend was found in the southeast of the Tibetan Plateau and Beijing-Tianjin-Hebei region. In humid regions, drought relieved in the Yangtze River Delta but worsened in the southwest of China. Changes in drought frequency and intensity also exhibited remarkable spatial heterogeneity. Our results can contribute to a better understanding of the spatial-temporal variations of drought severity for climate change adaptation.