Do changes in climate or vegetation regulate evapotranspiration and streamflow trends in water-limited basins?

Abstract. Interactions between climate change, vegetation, and soil regulate hydrological processes. In this study, it was assumed that vegetation type and extent remained fixed and unchanged throughout the study period, while the effective rooting depth (Z_e) changed under climate change scenarios. Budyko's hydrological model was used to explore the impact of climate change and vegetation on evapotranspiration (E) and streamflow (Q) on the static vegetation rooting depth and the dynamic vegetation rooting depth. Results showed that both precipitation (P) and potential evapotranspiration (E_p) exhibited negative trends, which resulted in decreasing trends for dynamic Z_e scenarios. Combined with climatic change, decreasing trends in Z_e altered the partitioning of P into E and Q. For dynamic scenarios, total E and Q were predicted to be −1.73 and 28.22%, respectively, greater than static scenarios. Although climate change regulated changes in E and Q, the response of Z_e to climate change had a greater overall contribution to changes in hydrological processes. Results from this study suggest that with the exception of vegetation type and extent, Z_e scenarios were able to alter water balances, which in itself should help to regulate climate change impacts on water resources.