Dry-wet variations and the related influencing factors in Southwest China on multi-time scales during 1961-2017

Dry-wet variations are a hot topic in global climate change research. Climate warming has led to the changes of evapotranspiration and precipitation are unevenly distributed, which have and will undoubtedly affect the dry-wet variations. In this study, based on daily climatic data from 423 meteorological stations in Southwest China (SWC), we analyze the trends and spatial variabilities of dry-wet climatic factors during 1961-2017, such as potential evapotranspiration (ET0), precipitation, and humid index (HI). Also, we investigate the possible influencing factors causing dry-wet variations. The results show that the arid, semi-arid, and humid regions decreased in 1991-2017 compared with those in 1961-1990, but the sub-humid regions increased. During 1961-2017, there was a noticeable decreasing trend in precipitation, while the variation trend in the ET0 was not apparent, which contributed to the dry climate in the SWC. The ET0 was most sensitive to temperature, followed by relative humidity. The contribution to the change of the ET0 was most remarkable for the change of temperature, followed by sunshine hours and wind speed. On the seasonal scale, the climate became drier in summer and autumn during 1961-2017, but there were no obvious wet-dry variations in spring and winter. Temperature and wind speed were the major factors causing the ET0 variation in spring and winter. Temperature, wind speed, and relative humidity were the critical factors contributing to the ET0 variation in autumn. while sunshine hours played a primary role in the ET0 variation in summer. On the monthly scale, the climate tended to be dry in most months, except for January, March, June, and July. Temperature was the most prominent contributor to the ET0 increase in most months. Also, wind speed and sunshine hours were the main factors of the ET0 reduction in October-May and June-September, respectively. This study can provide a specific reference for drought monitoring and early warning in different climate zones of the SWC.