Assessing the impact of climate variability and human activity to streamflow variation

Abstract. Water resources in river systems have been changing under the impacts of both climate variability and human activities. Assessing the respective impacts on decadal streamflow variation is important for water resources management. By using an elasticity-based method, calibrated TOPMODEL and VIC hydrologic models, we have quantitatively isolated the relative contributions that human activity and climate variability made to decadal streamflow changes in Jinhe basin located in northwest of China. This is an important watershed of Shaanxi Province that supplies drinking water for a population of over 6 million. The results from the three methods show that both human activity and climatic differences can have major effects on catchment streamflow, and the estimates of climate variability impacts from the hydrological models are similar to those from the elasticity-based method. Compared with the baseline period of 1960–1970, streamflow greatly decreased during 2001–2010. The change impacts of human activity and climate variability in 2001–2010 were about 83.5 and 16.5% of the total reduction respectively when averaged over the three methods. The maximum contribution value of human activity was appeared in 1981–1990 due to the effects of soil and water conservation measures and irrigation water withdrawal, which was 95, 112.5 and 92.4% from TOPMODEL, VIC model and elasticity-based method respectively. The maximum value of the aridity index (E₀/P) was 1.91 appeared in 1991–2000. Compared with 1960–1970 baseline period, climate variability made the greatest contributions reduction in 1991–2000, which was 47.4, 43.9 and 29.9% from TOPMODEL, VIC model and elasticity-based method respectively. We emphasized various source of errors and uncertainties that may occurre in the hydrological model (parameter and structural uncertainty) and elasticity-based method (model parameter) in climate change impact studies.