Quantifying the Impacts of Climate Change and Human Activities on Runoff in the Lancang River Basin Based on the Budyko Hypothesis

Based on the Lancang River Basin (LRB) hydro-meteorological data from 1961 to 2015, this study uses the Mann-Kendall trend test and mutation test to analyze the trend of hydro-meteorological variables, as well as which year the runoff series changes, respectively. We applied the Choudhury-Yang equation to calculate the climate and catchment landscape elasticity of runoff. Then we quantified the impact of climate change and human activities on runoff change. The results show that: (1) the mean annual precipitation (P) in LRB showed an insignificant decline, the annual potential evapotranspiration (E-0) showed a significant increase, and the runoff depth (R) showed a significant decrease; (2) the abrupt change of the R occurred in 2005. Both the climate and catchment landscape elasticity of runoff increased, which means that the hydrological process of LRB became more sensitive to climate changes and human activities; (3) compared with the base period (1961-2004), the reduction of P was the leading cause of runoff reduction, with a contribution of 45.64%. The contribution of E-0 and human activities to runoff changes are 13.91% and 40.45%, respectively.