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, the production of water-intensive commodities, and maintaining healthy ecosystems and economies. Rural areas play an outsized role in provisioning vital water resources to cities downstream that are principle locations of economic productivity, prosperity, and global populations. With increasing and unprecedented pressure on water resources from climate change, population growth, water use, land cover, and pollution, there is 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 (e.g., Viviroli et al., 2007 WRR), which are too coarse for water system-level decision making. Here we present a high-resolution water tower model that quantifies upstream-downstream dependency by spatially connecting downstream water use (e.g., public water supply) to upstream locations of runoff generation. We focus on the Potomac River watershed that provides ~75% of surface water used by the Washington, D.C. metropolitan area. Recent research suggests near future instances of water scarcity throughout the watershed due to population growth, increased water demand, and increased aridity due to climate-driven increases in atmospheric demand. Our high-resolution water tower model identified explicit locations within the watershed that play disproportionately large roles in providing freshwater to the D.C. metropolitan area, highlighting its dependence on the rural hinterlands. This research provides an innovative approach for prioritizing water resources management across the region for promulgating sustainable water resources management policies and enhancing water security.