Analysis of the dominant causes for runoff reduction in five major basins over China during 1960—2010

A sharp reduction of annual runoff has been observed during the past 50 years in five major river basins of China, namely Songhuajiang River, Liaohe River, Haihe River, Yellow River and Hanjiang River. In this study, changes of catchment runoff and their causes were investigated in 107 small catchments with relatively small artificial water uses from the 5 basins. The coupled energy-water balance equation based on the Budyko hypothesis is employed to estimate climate elasticity and landscape elasticity of runoff, which were then used for attribution analysis of runoff decrease in these 107 catchments. The results show that the catchment annual runoff is relatively less sensitive to climate and landscape changes in relatively humid regions while it is more sensitive to climate and landscape changes in relatively arid regions. By the attribution analysis, it is found that the change in potential evapotranspiration has little impact on runoff in most of the 107 catchments while the dominant factors leading to runoff reduction are the changes in precipitation and catchment landscape. It is also seen that the landscape change induced catchment runoff reductions have significantly intensified in the recent 10 years. Based on the analysis of NDVI (Normalized Difference Vegetation Index) during the recent 30 years, vegetation increase appears to be the dominant change in landscape. This implies that the soil and water conservation project carried out in China has achieved a notable ecological effect although it is also one of the major causes of runoff reduction.