HUMAN IMPACTS ON THE HYDROLOGIC CYCLE: COMPARING GLOBAL CLIMATE CHANGE AND LOCAL WATER MANAGEMENT

Anthropogenic climate change is significantly altering the hydrologic cycle at global and regional scales, with potentially devastating impacts on water resources. Recent studies demonstrate that hydrologic response to climate change will depend on local-scale interactions and feedbacks between groundwater, surface water, and land surface processes. These studies suggest that local water management practices that alter the quantity and distribution of water in the terrestrial system—e.g., groundwater pumping and irrigation—may also feed back across the hydrologic cycle, with potentially significant impacts on land-atmosphere fluxes and thus weather and climate. Here we use an integrated hydrologic model to compare the impacts of large-scale climate change and local water management practices on water and energy budgets at local and watershed scales. We consider three climate scenarios (hot, hot+wet, and hot+dry) and three management scenarios (pumping only, irrigation only, and pumping+irrigation). Results demonstrate that the impacts of local water management on basin-integrated groundwater storage, evapotranspiration, and stream discharge are comparable to those of changing climate conditions. However, impacts of climate change are shown to have a smaller magnitude and greater spatial extent, while impacts of pumping and irrigation are shown to have a greater magnitude but are local to areas where pumping and irrigation occur. Notably, our results underscore the importance of local hydrologic feedbacks in governing local hydrologic response to anthropogenic change. These results have important implications regarding the scale of human impacts on weather and climate and the sustainability of water resources.