H171-0017
Interbasin transfers extend the benefits of National Forest System Lands for water supply beyond downstream users

Tuesday, 15 December 2020
Poster
Ning Liu, University of Minnesota Twin Cities, Minneapolis, MN, United States, G. Rebecca Dobbs, ORISE, Otto, United States, Peter V Caldwell, US Forest Service, Southern Research Station, Otto, NC, United States, Chelcy Ford Miniat, USDA Forest Service Southern Research Station, Coweeta Hydrologic Laboratory, Otto, United States, Paul V Bolstad, University of Minnesota Twin Cities, Department of Forest Resources, St Paul, MN, United States, Stacy A. C. Nelson, North Carolina State University Raleigh, Forestry and Environmental Resources, Raleigh, NC, United States and Ge Sun, USDA Forest Service, Southern Research Station, Raleigh, NC, United States
Abstract:
Compared to other land cover types, forests provide the cleanest and most dependable water supplies to downstream communities. In addition to serving these downstream communities, water originating from forest lands is sometimes transferred hundreds of kilometers away to support people in big cities through inter-basin transfers (IBTs). The USDA Forest Service (USFS) manages more than 779,000 km2 of forests and grasslands across the conterminous United States (CONUS) that play a significant role in providing fresh water across the nation. Contribution of these National Forest System (NFS) lands to water supply through IBTs has not been considered in previous studies. Here we modified the USFS Water Supply Stress Index (WaSSI) model to account for water transfer through IBTs. Our model results provide estimates of mean streamflow and the proportion of mean flow originating on NFS lands (172 unique National Forests and National Grasslands) at the 12-Digit Hydrologic Units scale across CONUS. Predictions of the proportion of water originating on NFS land were linked to specific downstream communities and populations using surface drinking water intake information from the United States Environmental Protection Agency Safe Drinking Water Information System (SDWIS). Our preliminary IBT database included more than 350 IBTs transferring from 0.01 million m3 yr-1 to 4,764 million m3 yr-1 each. We found that more than half of IBTs transferred the majority of their water from NFS lands. Approximately 62 million people derived some portion of their drinking water supply from NFS lands without using an IBT. Almost 11.6 million people received greater than 50% of their drinking water supply from NFS lands. Another 3.5 million people derived the majority of their water from NFS lands via an IBT. NFS lands not only benefit and impact people living in the downstream communities, but also provide surface water for another 867,000 people living in other areas through IBTs. This study provides a systemic understanding of the importance of NFS lands in providing water for drinking water supplies. Our results can aid water resource and forest managers in developing integrated watershed management plans at a time when climate, population growth, and land development threatens water supplies.
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