Changes in extreme wet events in Southwestern China in 1960–2011

Based on climate data from 108 meteorological stations in Southwestern China and the spatial and temporal distributions of extreme wet events during the 1960–2011 period, the summer monsoon and winter monsoon periods are analyzed by calculating the monthly and yearly surface humid indexes, as well as the frequency of extreme wet events. The abrupt change and the period in the extreme wet events data sets are characterized using a comprehensive time series analysis conducted with a moving t-test and Morlet wavelet. The results indicate that the regionally averaged frequency of extreme wet events has slightly increased by 0.001 times/y over the study period. The frequency of extreme wet events tended to decrease in the 1960s, 1970s, 1980s, and 2000s, whereas in the 1990s, the frequency of extreme wet events (0.47 times/y) exhibited an increasing trend that is significantly larger than the average level in the study area. During the summer monsoon period, extreme wet events exhibit a slight decreasing trend with fluctuations. Nevertheless, the extreme wet events demonstrate an increasing trend at the rate of 0.007 times/y during the winter monsoon period, especially in Sichuan province. The spatial distribution of extreme wet events exhibits a rough uniformity. Overall, the frequency of extreme wet events decreases from west to east, except for several discrepancies in southwestern Yunnan province and southeastern Guangxi province during certain periods. The increasing number of regions that experience extreme wet events is likewise primarily distributed in the higher altitude areas. The abrupt changes obtained in 2002 and 1988 occur during the summer monsoon and winter monsoon period, respectively. The annual frequency variation is a superposition of abrupt changes during the summer monsoon and winter monsoon periods. The major cycle of extreme wet events in these two periods changes according to 26 y and 12 y over the study period.