Trends in water yield under climate change and urbanization in the US Mid-Atlantic region

Changes in climate and land use are two primary drivers of hydrologic adjustment. This study analyzes 40 years of water resources data for 10 watersheds in the Washington, DC metropolitan area to quantify the impact of climate change and urbanization on water yield. The watersheds investigated have experienced varying degrees of land-use change, from relatively little change to rapid and extensive urbanization. Comparing the data trends for different watersheds allows the separation of effects that are due largely to climate change from those due to land-use change. Predominantly rural watersheds show a steady decline in annual water yield, whereas predominantly urban watersheds do not show any similar trend with time. Separating the year into growing versus nongrowing seasons reveals that limited evapotranspiration from urban surfaces during the growing season or the general effects of a leaking water distribution network may mask the reductions in water yield in urban watersheds from changing climate. These analyses provide hydrological evidence for generally enhanced evapotranspiration and complex interactions between concurrent climate change and urbanization within the study area.