Differentiating Diversions and Drought to Understand Drivers of Water Loss from a North American Terminal Lake

Water levels on Mono Lake, an iconic terminal lake in North America's Great Basin, declined rapidly from the late 1940s to the early 1980s during a period of increased diversions. Our research investigated why water levels have remained chronically low, despite implementation of management plans limiting diversions starting in 1994. Restoring Mono Lake water levels requires a differentiation and understanding of historical drivers of hydrologic variability, and a propagation of that understanding into scenario-based water level management plans. We addressed this need by first reconstructing Mono Lake's historical water balance using a novel Bayesian inference model. We then used our new water balance component estimates to evaluate four climate and water diversion scenarios. We found that neither changes in climate nor diversions alone are solely responsible for the persistent low water levels on Mono Lake. Our results, including our new historical record and scenario analysis framework, provide important guidance to water resource management planners on why Mono Lake and other terminal lakes across North America have been, or are still, in chronic decline.