PNNL

Abstract

Climate change and human activities are known to have induced changes to hydrology. Quantifying the relative contribution of the impact of each factor on the hydrologic response of watersheds requires the use of some type of model. In this paper, a decomposition method based on the Budyko model is used to divide the relative contribution of climate and human on mean annual streamflow for 413 watersheds in the contiguous United States. The data of annual precipitation, runoff and potential evaporation of each of the watersheds are obtained from the international Model Parameter Estimation Project (MOPEX), which is often assumed to only include gages unaffected by human activities. The data is split in to two periods (1948-1970 and 1971-2003). The relative contributions of climate change and human activities to the observed change in mean annual streamflow between the two periods are estimated. Although climate change is found to impact annual streamflow more than human activities, the results show that assuming the dataset is unaffected by human activities is far unrealistic. Also climate and human induced changes are more stringent in arid regions where water is limited. The results are compared using four single-parameter functional forms and with previously published data.