Linking Downstream Water Use with Upstream Water Production - Insight from a High-Resolution Water Tower Model of the Potomac River Watershed

Water is the foundation of healthy communities, ecosystems, and economies. Clean, reliable water is critical for drinking, producing water-intensive commodities, thermoelectric power generation, and maintaining healthy ecosystems and economies. Rural areas disproportionately provision natural resources such as freshwater to downstream cities, which are primary locations of economic productivity, prosperity, and populations. Increasing and unprecedented pressure on water resources from climate change, population growth, water use, land cover, and pollution, creates a critical need to understand the dependency of downstream economies on upstream locations that provision freshwater supplies. Previous studies have substantiated upstream-downstream dependencies at continental- and country scales, which are too spatially coarse for meaningful basin-scale decision-making. This research presents a spatially explicit basin-scale water tower model (initially developed by Viviroli et al., 2007) that quantifies upstream-downstream dependence by spatially connecting downstream water users (e.g., public water supply) to upstream locations of runoff generation in addition to comparing the impact of different spatial resolution hydrologic datasets. We focus on the Potomac River watershed in the Mid-Atlantic Region of the United States of America, which provides ~75% of surface water supplies in the Washington, D.C. metropolitan area. Recent research suggests near-term scenarios with water scarcity throughout the watershed due to population growth, increased water demand, and increased aridity due to climate-driven increases in atmospheric demand. This basin-scale, gridded water tower model identifies spatially explicit locations and land cover within the watershed that disproportionately largely supply fresh water to the Washington, D.C. metropolitan area, underscoring its reliance on rural hinterlands. Our findings provide insights for basin-scale integrated water resource management planning by highlighting the potential impacts of land use changes and climate change on these critical water generation areas. We highlight the importance of decision-ready science in water resource management, particularly in domains such as water allocation, infrastructure planning, and ecosystem restoration. By leveraging geospatial data science and comparing high-resolution hydrologic datasets, this research provides actionable insights to guide decision-makers in developing strategies that ensure the long-term sustainability of water resources.