Quantifying the contributions of climate change and human activities on runoff changes is of great importance for water resource management, sustainable water resource utilization, and sustainable development of society. In this study, hydrological and climatic data from hydrological and meteorological stations in the headwaters of the Yangtze River (YRHA) from 1966 to 2013 were used to quantitatively attribute the runoff change to the impacts of climate change and human activities separately. Firstly, the change trends in precipitation, runoff depth and potential evapotranspiration were analyzed by the Mann-Kendall test method. Three methods, secondly, including ordered clustering, Mann-Kendall and cumulative anomaly curve were adopted to detect the change points of runoff at Zhimenda hydrological station and partition the whole study period into two sub-periods at the change point (base and impacted periods). Then, the elasticity coefficient method based on the Budyko hypothesis was applied to calculate elasticity coefficients of runoff to precipitation, potential evapotranspiration and land use/cover during the two periods, and to evaluate the contributions of climate change and human activities. Results indicated that during 1966–2013, runoff depth, precipitation and potential evapotranspiration all showed a significant increasing trend, with increasing rates of 7.26 mm decade−1, 18.725 mm decade−1 and 7.228 mm decade−1, respectively. One change point (2004) was detected for the annual runoff, and 1966–2003 and 2004–2013 were respectively identified as base and impacted periods. The results of elasticity coefficients showed that the runoff depth was most sensitive to the change of precipitation during the two periods. The relative contributions of precipitation, potential evapotranspiration and parameter n to runoff changes were 99.7%, −6.08% and 3.88%, respectively. Furthermore, the coupled contribution rate of other factors was less than 2.5%. Generally, results indicated that precipitation is the main factor on the historical runoff changes in this basin.

To reasonably evaluate the water resource security state, this research built a water resource security evaluation index system of the Yangtze River Economic Belt (YREB) based on the driving force-pressure-state-impact (DPSI) concept framework, established a water resource security evaluation model by combining the entropy weight method with the fuzzy set pair analysis method and conducted quantitative evaluations of the water resource security states from 2008 to 2016. All the work above was based on the comprehensive consideration of the water resource characteristics in different areas of the YREB, following the index system construction principles. The results have shown that on the whole, the water resource security state of the YREB has generally undergone a process from getting worse to getting better in the latest nine years. From the aspect of the percentages of the water resource security grades, the spatial distribution of water resource security in the YREB is highest in the downstream area, second in the middle reaches, and lowest in the upper reaches. From the aspect of the DPSI security evaluation results, the driving force and state of the water resource are the important factors affecting the water resource security of the YREB.

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