Effect of rainfall variation and landscape change on runoff and sediment yield from a loess hilly catchment in China

The semiarid Chinese Loess Plateau is notorious for severe drought, water erosion, and environmental degradation. Changes in landscape patterns and rainfall are key drivers that determine the dynamics of runoff loss and sediment yield from catchments. These factors have crucial implications for management of other fragile ecosystems around the globe. In this study, responses of surface runoff and sediment yield to land use and rainfall in a typical loess hilly catchment in 1997, 2005, and 2010 were analyzed. Several major findings are highlighted. First, most rainfall occurred in the growing season from June to September and increased only slightly during the observation years. Second, runoff and soil transport rates at the catchment outlet from June to August were far greater than in other months. A similar trend was observed for seasonal rainfall occurrence, indicating that the intra-annual water erosion patterns were largely dominated by monthly rainfall distribution. Third, compared with the time period 1997-2005, mean runoff and sediment transport modulus in 2005-2010 declined significantly. This can be attributed mainly to changes in land use/land cover, i.e., increases in forests, shrubs, and grasses, and decreases in sloping farmlands. Dam construction is also key in controlling runoff and sediment yield, but more attention must be paid to its possible negative environmental effects. In general, our study indicates that marked changes in landscape patterns and vegetation coverage may contribute to long-term soil loss dynamics, and intra-annual rainfall variation mainly contributes to monthly variation in runoff and sediment yield.