Estimating reservoir evaporation: Evaluating current and future practices and research-to-operations pathways

Reservoir evaporation has received negligible attention within high-level planning of water resource infrastructure in the arid western United States. This is primarily due to both practical and logistical challenges and large uncertainties in its estimation. With demand eclipsing supply for many users in the Colorado River Basin and Sierra Nevada Mountains, reservoir evaporation is of increasing importance given broad uncertainties in precipitation magnitude and timing with climate change, and the occurrence of recent and historical decade-long droughts. Evaporative water loss has heretofore been estimated with outdated procedures that are insensitive to critical climate factors and spatial heterogeneity. This presentation will describe the outcomes of a reservoir evaporation workshop held in Boulder, Colorado, October 21, 22, 2015, that included recognized experts in the field of atmospheric science, hydrology, land use, and water resource management. The goals of the workshop were to: (a) assess current practices for estimating reservoir evaporation and to develop a research program to inform operational reservoir evaporation estimation, (b) quantify the evaporation potential of current reservoirs and provide scientific guidance for reducing evaporation in current, augmented, and newly-built reservoirs, (c) introduce research-to-operations practical methods to monitor and forecast reservoir evaporation, and (d) develop a scientific plan using state-of-the-art scientific methods and instrumentation to explore reservoir evaporation forecasting potential, and begin the transfer of this technology to the water management community. An overarching concept driving the workshop discussions was the idea of “Conservation At the Source - CAS”, a physically-based assessment for the augmentation of existing and placement of new reservoirs.