Assessing Climate Change Impacts on Yield of “Dual-Priority” Water Rights in Carryover Systems at Catchment Scale

Future water availability is threatened by changes in both climate and water demand. Water rights with differing priorities are an important foundation of demand-side tools (e.g., buyback, water pricing, and water market) to improve water use efficiency and reduce water scarcity, especially in highly regulated river systems. This paper assesses the impact of climate change on water yields from carryover storage with dual-priority (high/low) water rights allocation systems using a simple and rapid analytical method. The method characterizes reservoir inflows using readily available flow characteristics (annual mean and C_v). We evaluate this method against a water resource simulation model in the Goulburn River basin, Australia. In general, our analytical “dual-priority” Gould-Dincer model reproduces water allocation estimates from the simulation model. We further demonstrate this method across 12 Australian catchments to investigate the climate change impact on “dual-priority” water rights yield at the catchment scale. The hydrological projections show decreasing mean annual runoff and increasing annual runoff variability, except for some catchments in northern Australia. Water yield for high-priority water rights (HPWRs) and low-priority water rights (LPWRs) decreases for most catchments except for some catchments in northern Australia. South Dandalup in the 2070s (RCP8.5) shows the largest percentage decrease in HPWR and LPWR yield (about −53.53% and −56.81%, respectively). Our results show that changes in mean annual inflow have a more significant influence on water yield of HPWR and LPWR than C_v. Overall, the simple method provides a rapid assessment of water yields with “dual-priority” water rights which is applicable across multiple sites at regional or even global scale.