Future Drought Changes in China Projected by the CMIP6 Models: Contributions from Key Factors

Model simulations show that drought may become more severe and widespread in the 21st century due to human-induced global warming. However, the contributions from the key factors to the model-projected drought changes in China have not yet been examined in detail. We used the self-calibrated Palmer Drought Severity Index with Penman–Monteith potential evapotranspiration (scPDSIpm) based on 10 model simulations selected from the Coupled Model Intercomparison Project Phase 6 (CMIP6). We investigated the contributions from precipitation (P), near-surface air temperature and specific humidity Δ(T + q), net surface longwave radiation (LW), net surface shortwave radiation (SW), and wind speed (WS) to the future changes in scPDSIpm, including the long-term mean, drying area, probability distribution function (PDF), drought frequency, and drought duration based on the scPDSIpm over China. Our results show that model-projected drying mainly occurs over southern China, whereas the dry areas under drought conditions increase from 20% to about 23%/30% under the two scenarios of the shared socioeconomic pathway (SSP2-4.5/SSP5-8.5) from 1985 to 2100, despite large uncertainties in individual projections partly due to internal variability. Drought frequency is projected to increases by about 10%–54% (15%–88%) under the SSP2-4.5 (SSP5-8.5) scenario by the late 21st century, along with increases in drought duration. These changes are accompanied by a decrease in the mean scPDSIpm and flattening of the PDFs. The changes in drying over southern China are mainly attributed to surface warming and the increased surface vapor pressure deficit (VPD), with small contributions from changes in the surface net radiation. The changes in wetting over northern China mostly result from increased precipitation along with a small wetting effect from the changes in wind speed.