Detecting the quantitative hydrological response to changes in climate and human activities.

Understanding the relative contributions of climate change and human activities to changes in runoff is important for sustainable management of regional water resources. In this study, we systematically review ten commonly used quantitative methods drawn from three main categories-empirical statistics, elasticity-based methods, and hydrological modeling. We explain the calculation processes for the different methods and summarize their applications and characteristics. Then, using the Yanhe River basin as a case study, we employ all ten methods to separate out the effects of climate change and human activities on changes in runoff. The results show that climate change played a dominant role in the decline in runoff in the Yanhe River basin. Climate change was estimated to account for 46.1%-60.8% (mean 54.1%) of the total decrease in runoff, whereas human activities accounted for 39.1%-53.9% (mean 45.9%). Elasticity-based methods and hydrological modeling produced similar estimates, but the estimates made using empirical statistics were different. Empirical statistics were not a suitable method for the Yanhe River basin. We also discuss the factors that influence the different methods and the applicable conditions for each methodological category.