Quantifying the Impact of Climate Change and Human Activities on Runoff Reduction with Sensitivity Analysis on Time Series Breakpoints

In this paper, the Impacts of Climate Change and Human Activities on Runoff Reduction (ICHRR) are quantified using three approaches based on regression, climate elasticity and water balance models. These approaches are based on finding the location of the occurring an abrupt statistical change (breakpoint) in runoff time series. In this paper, the effect of locating the breakpoint(s) on the mentioned quantified impacts is studied through sensitivity analysis. The performance of the mentioned three approaches is evaluated by applying them on Zayandehrud river discharge which is subjected to significant human induced changes such as dramatic increase of the area of agricultural lands and inter-basin water transfer projects. The water balance model is calibrated and verified for the period of 1976 to 1984. The sensitivity analysis shows that among several years with potential of the occurring a breakpoint, considering the year of 2006 as the breakpoint, the estimated values of ICHRR are more realistic. These results are in accordance with the observations including the time series of climate variables, agricultural land areas and inter-basin water transfer discharge. Also, if the impact of inter-basin water transfer on increasing runoff is removed from the runoff time series, the impact of climate change on runoff reduction based on all the three approaches is mostly close to zero.