Projected dry/wet regimes in China using SPEI under four SSP-RCPs based on statistically downscaled CMIP6 data

Dry/wet conditions are one of the key constituents of climate change. The understanding of dry/wet variability is vital for production and water resources management. In this research, the temporal variations of 12-month timescale standardized precipitation evapotranspiration (SPEI) over 2021-2100 under the SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5 scenarios in seven subregions and China's mainland were investigated over the baseline period of 1961-2000. The run theory was used to project the variations of dry/wet frequency, duration and severity at different levels during 1961-2000, 2021-2060 and 2061-2100 based on the estimated SPEI. The results showed that dry tendency would occur in northwest China. The linear trend for SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5 were -0.056, -0.031, 0.009 and -0.072 per decade, respectively. While wet tendency would occur in the other regions over 2021-2100. The mild, moderate and severe dry/wet duration and severity over 2021-2060 and 2061-2100 would gradually decrease. Except for northwest China and Qinghai-Tibetan Plateau, the extreme drought duration and severity would increase in the other subregions, while the extreme wet duration and severity would increase in most regions of China. The drought frequency in north China would range from 0 to 14 times and be smaller than the other regions over 2021-2060 and 2060-2100. However, the wet frequency in south China would be larger than that in the other regions. The dry/wet frequency duration and severity for the SSP5-8.5 scenario would be the largest among the four scenarios. The projected dry/wet conditions can provide useful information for future water resources management.