Is Southwest China drying or wetting? Spatiotemporal patterns and potential causes.

With significant climate warming, droughts over Southwest (SW) China are drawing increasing interest. By using the Mann-Kendall trend test, the continuous wavelet transform (CWT), the rotated empirical orthogonal function (REOF), and the random forest method (RF), this study focused on the trends and spatial variability in wetness/dryness as well as further investigated the potential factors by analyzing the behaviors of precipitation, temperature, and teleconnection indices in SW China. Results show that there are a slight drying trend and a remarkable spatial variation in the patterns of wetness/dryness. Due to the decreasing precipitation and increasing temperature, the drying trend (especially for severe and extreme droughts) significantly increases in the Yunnan-Guizhou Plateau and the Chongqing-Hubei region in the past decades. Additionally, the droughts in this region may also be directly or indirectly affected by the complex karst topographic and hydrological process. The variable importance analysis between climate index and standardized precipitation evapotranspiration index (SPEI) suggests that Atlantic Oscillation (AO) and Sunspots (SS) are the two most important influencing factors for the variations in dryness/wetness over SW China. Particularly, SS (AO) can be the largest influencing factor for the Yunnan-Guizhou Plateau and the Chongqing-Hubei region (Northern and Central Tibet). Besides, El Niño-Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Indian Ocean Dipole (IOD), and Pacific Decadal Oscillation (PDO) indices also show an impact on the variations in dryness/wetness, but their contributions are different in different regions. The results of this study provide certain references for mitigating the potential widespread impact of drought hazards in SW China. [ABSTRACT FROM AUTHOR]