Quantifying the effects of climate and watershed structure changes on runoff variations in the Tao River basin by using three different methods under the Budyko framework

Quantifying the effects of climate change and catchment structure changes (like anthropic activities) on runoff variations effectively and accurately is always a challenge for hydrological community. In this study, three widely used methods: climate elasticity method, Budyko curve decomposition approach, and hydrologic simulation method, were applied in the Tao River basin, a typical first-order tributary of the Yellow River basin. The results indicated that the annual runoff of the Tao River basin dropped significantly, especially after 1986, with the changing rate of -13.66 mm/10a during the research period (1956-2014). According to the attribution results, in the moderate influenced period (1969-1986), the climate change was less influential than watershed structure changes to runoff variations, while after 1986, about 45% of the total decline in mean annual runoff were caused by the decreasing P and the significant rising air temperature, which enhances the watershed evaporation, and about 55% was probably attributed to watershed structure changes. There were systematic deviations between results from two Budyko-based conceptual approaches and hydrologic simulation method. The Budyko-based decomposition method tends to attribute more runoff variations to changes in watershed structure, while the hydrologic modeling approach tends to emphasize the influence of climate change on runoff changes at catchment scale. The difference in effect quantification is attributed to the errors in the mean annual runoff naturalization during the postchange period. The impacts of watershed structure changes induced by climate change (like vegetation condition changes) on runoff variations may fall into the human impact category in attribution calculation.