Decomposing the Effects of Changes in Catchment Characteristics on Runoff Into Chain Transmission Effects of Climate Change and Human Activities Using an Improved Budyko Framework

Effect of catchment characteristics (e.g., land use/land cover changes) is increasingly accepted as the main cause of runoff changes, besides direct effects of climate change and human activities. However, previous studies usually attributed this effect to human activities, and ignored the effect of climate changes, namely chain transmission effects via catchment characteristic alterations. This study proposes a novel assessment approach of runoff change to disentangle both direct and chain transmission effects by adopting nonlinear relationships between catchment characteristic parameters and multiple impact factors into the Budyko framework. Eight catchments in the arid and semi-arid, semi-humid, and humid climatic zones are selected as our study area. Results show that runoff in most catchments decreases, while catchment characteristic parameters increase, with slopes of −2.44 to 3.79 mm/year and −0.003 to 0.017/year, respectively. It indicates that more precipitation evaporates than that contributing to runoff due to the catchment characteristic alterations. These changes are the most significant in the semi-humid zone, followed by those in the arid and semi-arid zone. Annual temperature and precipitation, gross domestic product, industrial water use, and population are the main impact factors. The contributions of human activities to runoff changes are usually the largest (i.e., −62.9% to 72.0%), followed by the direct effects of climate change (i.e., −32.6% to 88.0%). The chain transmission effects of climate change are also nonnegligible, with the contributions of −38.3% to 8.2%, particularly in the semi-humid zone. Our study improves the traditional Budyko-based framework for attributing runoff changes and provides scientific support for understanding hydrological cycle change mechanisms in climate-sensitive areas.