Effects of Extreme Rainfall Change on Sediment Load in the Huangfuchuan Watershed, Loess Plateau, China

Rainfall-induced erosion is a predominant factor contributing to land degradation, with extreme rainfall events exerting a significantly greater impact than average rainfall. This study investigates the variability of extreme rainfall events and their effects on sediment yields within the Huangfuchuan watershed, located in the middle reaches of the Yellow River. Utilizing daily rainfall data from ten rainfall stations and sediment load records from Huangfu Station spanning from 1980 to 2020, the Mann–Kendall non-parametric test, Pettitt test, and double mass curve analysis were carried out to assess four critical extreme rainfall indexes: daily rainfall exceeding the 95th percentile (R95p), maximum one-day rainfall (RX1day), maximum five-day rainfall (RX5day), and simple daily intensity index (SDII) and quantitatively evaluated the contribution rate of extreme rainfall to changes in sediment load within the watershed. The results revealed that during the period of study, all four extreme rainfall indexes demonstrated non-significant declining trends, whereas sediment load exhibited a highly significant decreasing trend, with abrupt changes in 1998. Prior to these changes, significant correlations were observed between extreme rainfall indexes and sediment load. From 1999 to 2020, the contribution rates of these indexes to changes in sediment load varied between 11.3% and 27.1%, with R95p showing the greatest impact and RX5day the least. The NDVI showed a significant increase (p < 0.05) and the amount of sediment retained and dam areas of check dams increased annually. This could be the main reason for the decrease in sediment load. This study clarifies the interactions between sediment load and extreme rainfall, which can be valuable for watershed management decisions.