Quantifying the Impacts of Climate Change and Human Activities on Runoff Variation: Case Study of the Upstream of Minjiang River, China

Quantifying the impacts of climate change and human activities on runoff variation has drawn considerable concern. In this study, a modified method of slope change ratio of accumulative quantity (modified SCRAQ) has been proposed to estimate the contributions of climate change and human activities on runoff variation. The variation characteristics of hydrometeorological series were detected in the upstream of Minjiang River (UMR), China, during 1960-2012 using the Mann-Kendall test. The contributions of climate change and human activities on runoff variation in the UMR were estimated using the double mass curve method and modified SCRAQ method. The results showed that annual precipitation of the UMR had an insignificant decreasing trend, annual mean temperature presented a significant increasing trend, and annual runoff exhibited a significant decreasing trend. The years of 1969 and 1995 are taken as representative abrupt change points; the total study period was divided into the natural period (1960-1969) and change period (1970-2012), which includes 1970-1995 and 1996-2012. Precipitation caused the decrease of runoff except for the change period of 1970-1995; mean temperature led to the increase of runoff in each change period. Furthermore, runoff in the UMR was more sensitive to variation of mean temperature than that of precipitation. Under their combined influence, climate change resulted in the increase of runoff; human activities (e.g., agriculture irrigation, deforestation and afforestation, and urban water supply, as well as the construction of large reservoirs and dams) caused the runoff reduction. Overall, the impacts of climate change and human activities on runoff varied differently in the UMR, and human activities were the main driving factor leading to runoff variation. The results in this study can provide necessary information for water resources management in the UMR.