Human activities and climate simultaneously affect water cycling and provision. Here, we study the impacts of climate variability and human activities on green and blue water provision (or the flows of both green water and blue water) in the inland Heihe River Basin as simulated by the Soil and Water Assessment Tool (SWAT). The results show that total green and blue water flow varied significantly from 1980 to 2010. Direct human activities did not significantly change the sum of green and blue water flow volumes. However, land use change led to a transformation of 206 million m3/year in the entire river basin from green to blue water flow, while farmland irrigation expansion resulted in a transformation of 66 million m3 from blue to green water flow. The synchronous climate variability, with an upward precipitation trend, caused an increase of green water flow by 469 million m3/year and an increase of blue water flow by 146 million m3/year at the river basin level over the study period. The results provide a general approach to investigate the impacts of historical human activities and climate variability on water provision at the river basin level.

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