Untangling the effects of future climate change and human activity on evapotranspiration in the Heihe agricultural region, Northwest China

Abstract Evapotranspiration (ET) is the component of the hydrological cycle that accounts for most water consumption across the agricultural region of the Heihe River basin in Northwest China. It is of great practical importance in the basin to allocate water resources for ensuring the security of food production, and to formulate effective science-based agro-ecological management policies to address climate change impacts due to the probable effects of future changing environment on regional ET. In this study, the Soil and Water Assessment Tool (SWAT) model were first driven by the downscaled climate data from three IPCC representative concentration pathways (RCPs) that have been projected by five General circulation models (GCMs) in the Coupled model intercomparison project phase 5 (CMIP5) and the water-saving irrigation scenario to project ET per unit area, we then added to the model the upper and lower limits of the appropriate agricultural scale that considered the ecological health to simulate the behaviour of total ET for the period 2021–2050. Finally 12 case study scenarios were used to separate the effects of climate change and human activity on total ET. The results showed that ET per unit area increased by at least 10.65 mm under the RCP–water-saving irrigation scenarios, while total ET can be significantly decreased by more than 1.22×108 m3 when the RCP–water-saving irrigation scenarios were combined with the appropriate agricultural scale. The results suggest that the best set of strategies to reduce agricultural water consumption is to reduce the area of arable land through consideration of ecosystem health and aggressively utilize water-saving agricultural technology to counter the increased ET brought about by future climate change in the Heihe agricultural region.