Analyzing Variation Trends in Extreme Precipitation Events in the Jing River Watershed during 1965-2005

Extreme climate events often cause more damages to society and ecosystems than do simple shifts in the mean values, and the impacts of extreme precipitation events are one of the most critical reasons causing severe soil and water loss over the Loess Plateau. Therefore, variations trends in extreme precipitation events need to be reasonably assessed, which can provide meaningful information on regional ecological conservation. The authors performed a study on the Jing River watershed using daily precipitation data from 18 meteorological stations during 1965-2005. Extreme precipitation events were defined in terms of percentile values. Indices, such as amount, frequency, intensity and severe drought frequency, were used to quantify the extreme precipitation events. The Mann-Kendall test and wavelet analysis method were employed to analyze the monotonic trend, abrupt change, interdecadal change and the period of each index. Results showed that the mean annual amount of extreme precipitation events was 143.9 mm/a, accounting for 27% of the total amount of annual precipitation. The mean annual frequency, intensity and maximum daily amount of extreme precipitation events were 3.6 d/a, 39.8 mm/d and 52.3 mm/d, respectively; while the mean annual frequency of severe drought was 7.4 times/a. Most stations in the Jing River watershed had no significant monotonic trend in each selected index of extreme precipitation events; however, the frequency and intensity of extreme precipitation events tended to increase. Furthermore, the variation trends in extreme precipitation events exhibited spatial variability, which might be caused by the integrated effects of terrain, meteorological conditions and global warming. Specifically, there was a positive trend in extreme precipitation events in the middle and lower reaches of the river that was generally in line with the dominant change trends; while a negative trend in extreme precipitation events in the southwestern and northern watershed was detected, which was opposite to the dominant change trend. Each index was fluctuating during 1965-2005; however, they all increased since 1985 and showed several abrupt changes around the year 2000. The oscillating periods of all indices were found to be 2-3 a, 7-8 a, 13 a and 17 a. Though the annual precipitation amount had a slightly downward trend, each index of extreme precipitation events showed an insignificant upward trend. Therefore, the changes in extreme precipitation events should be paid more attention compared with annual precipitation amount due to potential catastrophic damages resulting from extreme precipitation events to water and soil loss. The findings of this study implied that extreme precipitation events in future might cause more severe adverse influences on soil and water conservation in the Jing River watershed. Therefore, some adaption actions should be taken to mitigate the adverse effects of climate change on human and natural systems.