Long-term change of wet and dry climatic conditions in the southwest karst area of China

• Detect the changing characteristics of temperature, and wet and dry conditions in Southwest China
• Temperature has increased significantly over the entire region.
• Wet conditions have obvious spatial and seasonal distinctions.
• Extreme droughts tend to occur frequently in recent years.

Using the daily precipitation and temperature data at 153 stations in the karst area of Southwest China from 1959 to 2009, the long-term change characteristics of wet and dry climatic conditions are analyzed by the Mann–Kendall test. This study shows that: 1) the annual average temperature has increased at 88% of the stations with an average rate of + 0.16 °C/10-year. This increase rate is greater than + 0.30 °C/10-year in the southeastern, northeastern, and western parts of the study region. Very warm days and abnormally warm days were seen increased at 47% and 63% of the stations, respectively. Very cool days and abnormally cool days in a year have reduced at respectively 94% and 95% of the stations; 2) no clear change trend was found for average annual precipitation over the entire area as a whole, but regional and seasonal changes were quite obvious. The annual total precipitation has decreased by − 22.5 mm/10-year in the central part but increased by + 8.9 mm/10-year in the western part of the region, and summer and winter seemed to become wetter while spring and autumn became drier. Although the number of rainy days in a year has decreased at almost 53% of the total stations with an average rate of − 3.9 days/10-year over the entire area, the number of extremely heavy rainy days has increased by + 0.2, + 0.4 and + 0.4 days/10-year in the southern Sichuan Province, the central part of Yunnan Province, and the northeastern Hubei Province, respectively; and 3) the extreme drought became more serious. The consecutive dry days has increased significantly at nearly 46% of the stations, especially in the western Guangxi Autonomous Region, the southern Guizhou Province, and the eastern Chongqing Municipality. The extreme drought remained at a high frequency at the beginning of the 21st century. It has shifted gradually from the eastern and western parts to the south-central part which is characterized by medium-high rocky desertification. Hopefully findings from this study will help for a better understanding of the impacts to some eminent geological hazards such as rocky desertification, increased frequency of drought and storms, and landslides in recent years.