Synthetic Impacts of Internal Climate Variability and Anthropogenic Change on Future Meteorological Droughts over China

The climate change impacts on droughts have received widespread attention in many recent studies. However, previous studies mainly attribute the changes in future droughts to human-induced climate change, while the impacts of internal climate variability (ICV) have not been addressed adequately. In order to specifically consider the ICV in drought impacts, this study investigates the changes in meteorological drought conditions for two future periods (2021-2050 and 2071-2100) relative to a historical period (1971-2000) in China, using two multi-member ensembles (MMEs). These two MMEs include a 40-member ensemble of the Community Earth System Model version 1 (CESM1) and a 10-member ensemble of the Commonwealth Scientific and Industrial Research Organization Mark, version 3.6.0 (CSIRO-Mlk3.6.0). The use of MMEs significantly increases the sample size, which makes it possible to apply an empirical distribution to drought frequency analysis. The results show that in the near future period (2021-2050), the overall drought conditions represented by drought frequency of 30- and 50-year return periods of drought duration and drought severity in China will deteriorate. More frequent droughts will occur in western China and southwestern China with longer drought duration and higher drought severity. In the far future period (2071-2100), the nationwide drought conditions will be alleviated, but model uncertainty will also become significant. Deteriorating drought conditions will continue in southwestern China over this time period. Thus, future droughts in southwestern China should be given more attention and mitigation measures need to be carefully conceived in these regions. Overall, this study proposed a method of taking into account internal climate variability in drought assessment, which is of significant importance in climate change impact studies.