Author(s)

M. E. Barber, J. Adam, K. Rajagopalan, G. Yorgey & R. Mahler

Abstract

Water rights in the western United States are granted under the prior appropriation doctrine; essentially first in time, first in right. Because many rights were issued prior to instream or ecological flow requirements, regulatory agencies have little authority to curtail diversions even when critical endangered species habitat is threatened. Compounding the issues is that municipal water rights throughout the Columbia River Basin were issued with significant \“inchoate” portions (unused) that threaten sustainable water management as climate change and population growths alter instream flows. In many regions, this is placing challenging restrictions on management for endangered species such as salmon and bull trout species. This is slowly evolving into policies such as the one adopted by the state of Washington where state investment in water projects reserves at least 1/3 for instream uses. We developed a combined VIC/CropSyst model that predicted water supply changes in the Columbia River watershed (7 states and a portion of British Columbia) due to climate change in the 2030’s and, by examining municipal water plans and population growth models, predicted future water demands within existing water rights and evaluated impacts to instream flows. There is an expected 26% increase in municipal demand (700 MCM) in the State of Washington alone with just over 50% being consumptively used. Other upstream communities in Idaho, Montana, and Oregon face similar situations to varying degrees. Results indicated that communities located on several tributaries will

Keywords

instream flow requirements, endangered species, climate change, prior appropriation doctrine