Water Resources Criticality Due to Future Climate Change and Population Growth: Case of River Basins in Utah, USA

Abstract

This study investigates annual river basin–level water criticality (ratio of available water to withdrawals) considering effects of climate change on supply and of future population change on demand. A steady-state water balance model was developed to estimate the water mass budget and disaggregate the internal and external water supply sources at a river basin level. Future precipitation and evapotranspiration were dynamically downscaled under a moderate greenhouse gas emission scenario to 4-km horizontal resolution using a regional climate model for a decade centered on 29. The climate data were also statistically downscaled via the bias correction spatial disaggregation (BCSD) method applied to the CMIP5 (the fifth phase of the Coupled Model Intercomparison Project) archives for four emission scenarios for decades centered on 24 and 29. Bootstrapping and k-nearest-neighbor (k-NN) algorithms were applied to simulate future water demand and external basin supply with uncertainty. Water stress is classified into four levels: (i) “very high-water stress” when the water criticality ratio <1.25, (ii) “high water stress” when criticality ranges from 1.25 to 2.5, (iii) “moderate water stress” when criticality ranges from 2.5 to 1, and (iii) “no water stress” when criticality >1. A basin with a criticality ratio of 1 indicates that the basin demand has been exactly met by the available supply sources. Most river basins have current water criticality less than 2 and are dependent on inflow from other basins (i.e., are not self sustaining). Future projections indicate modest increases in net available water for Utah through the end of the current century from climate change, with increasing vulnerability largely driven by population growth. Out of 11 basins, 4 achieve a high and 3 achieve a very high water stress status by the 24s. Four basins achieve a very high water stress status by the 29s compared to only two in a very high water stress status in the 21s.