| Summary: | Assessing the impacts of both climate and land use changes on hydrologic variables is crucial for sustainable development of water resources and natural ecosystems. We conducted a case study of a catchment in southwestern Australia to assess the impacts of future climate and land use changes, both separately and in combination, on water resource availability. For this evaluation, the Soil and Water Assessment Tool (SWAT) model was first calibrated and then forced by 34 global climate models (GCMs), under two Representative Concentration Pathways (RCP4.5 and RCP8.5) and five land use scenarios (LU0–4). Our results suggested that SWAT reproduced the observed monthly streamflow well. Land use changes have impacts on all hydrologic variables, especially on runoff at the annual scale. Future runoff was projected to decrease in all seasons, especially winter and spring. For the combined effects of climate and land use changes, the results of LU1–4 were only slightly different from the response of LU0. An uncertainty analysis shows that GCMs had the greatest contribution to hydrologic variables, followed by RCPs and land use scenarios. Hence, it is advisable for impacts analysis to use an ensemble of GCMs under different RCPs to minimize the uncertainty of projected future hydrologic variables.
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