Evolutionary effect separation of watershed characteristics for the multi-source contributions to runoff changes in the Yellow River, China

Traditionally, consideration of the contributors to runoff change includes only climate change and human activity. Furthermore, the runoff change effects of traditional climate change include non-climate change components. This could cause a problem of two-source unclosed calculation that total runoff change doesn't equal the dual contributions from climate change and anthropogenic influences. This study uncovers that the two-source unclosed problem is related to the natural evolution in the watershed characteristics (WCs), which is called the evolutionary effect of WCs (EEWC). A theoretical framework was proposed to separate the three-source areal changes of WCs from climate change, two types of anthropogenic influence, and EEWC. The three-source contributions to runoff changes were quantified through three hydrological models and the observability and controllability model of periphery. The EEWC was innovatively proven and demonstrated in the upper and middle Yellow River of Northwest China. The WCs were expressed by land use/land cover (LULC) and soil/water conservation measures (SWCMs) in this study. Hydrometeorological data, water utilization data from different sectors, and areal data of LULC and SWCMs on the annual scale during 1956-2015 were employed. The contribution of climate change on runoff changes was innovatively divided into the one from the changing area of WCs and the other one from the unchanged area of WCs. Two non-climate change components from traditional climate change contributions were separated. The EEWC has an important influence on areal change of WCs and is more stable in comparison with meteorological elements and anthropogenic influences. The framework is flexible regarding the use of referenced/change periods. The results overcome the shortcomings of traditional approaches and further improve the traditional two-source rationale to the three-source effects of climate change, anthropogenic influence, and EEWC.