Spatiotemporal variation of erosive rainfall and its influence on sediment discharge in the Ganjiang River Basin

Expected increases in extreme rainfall events due to global warming could lead to increased soil erosion in mountainous areas. In order to study this impact on specific areas, the present study identified the spatiotemporal variation of erosive rainfall and the influence of its variation on streamflow and sediment discharge within the Ganjiang River Basin. Daily average rainfall data were obtained from 23 national meteorological observation stations along with streamflow and sediment concentration data collected for 1964-2013 at 6 control stations. The nonparametric Mann-Kendall method and Pettitt test were used for trend analysis and changepoint detection, and the modified double mass curve method was used to quantify the effects of both erosive rainfall variation and human activities on hydrological regime shifts. Results showed significant monthly variation in erosive rainfall and significant increases in rainstorms over the entire watershed, particularly in the downstream subzone and northeast corner of the upstream subzone. While moderate rain showed an insignificant decrease in both subzones and the entire watershed, heavy rain showed no significant variation over the entire watershed but did show a significant increase in both the midstream and downstream subzones. The changes in accumulative erosive rainfall had only small effects on reduction in sediment discharge after the changepoint year. In contrast, human activities contributed to more than 50% of the changes in sediment discharge in the entire basin. These findings provide a research basis for the study of extreme climate, flood disaster prevention, and soil erosion prediction over the entire watershed.