Long-term change in precipitation structure over the karst area of Southwest China

This research analyses the long-term changes in the precipitation structure over the karst area of southwest China, as recorded by 153 national meteorological stations from 1959 to 2009. Study results are as follows: (1) The karst area of southwest China is categorized into six similar precipitation clusters, including two low-rainfall clusters located in the western and northern areas and four high-rainfall clusters distributed in the eastern and southern areas. (2) Although the decreasing trend of annual total precipitation is weak, autumn precipitation decreases significantly over the whole study area. The autumn total precipitation decreases significantly at 51% of the stations because the autumn wind and water vapor flux of the study area gradually decreased, and the autumn low-latitude and mid-latitude sea surface temperature (SST) of East Asia continues to rise and gradually leads to positive sea anomalies. (3) The number of rainy days decreases at 85.6% of the stations, especially in the central and southeastern regions of the area. Consequently, almost 53% of the total stations are characterized by an increasing precipitation intensity. (4) The occurrence time of the accumulated percentage precipitation in the western mountain areas is usually later than that in the eastern coastal areas, and the occurrence date of accumulated percentage precipitation (DAP) seems to occur increasingly earlier over the whole study area. (5) Light rain occurs more frequently (76% of annual total rainy days) and contributes 25% to annual total precipitation, whereas although heavy rains such as storms occur less frequently at 3% of annual total rainy days, it contributes almost 19% to annual total precipitation. (6) The occurrence and contribution of wet periods (WPs) decrease with an increase in their duration. WPs with short durations (e.g. 1-4 days) tend to be the predominant precipitation events.