Hydrologic Science Opportunities to Better Understand Water Demand: A Community Perspective

<jats:p>Water Demand focuses largely on terrestrial evapotranspiration (ET), including its drivers, uncertainties, feedbacks, and societal applications. ET refers to canopy transpiration, soil evaporation, and terrestrial open water evaporation and also includes ice and snow sublimation. Given the importance of soil water as both a source and a limiting factor for ET, our focus also includes the characterization of soil moisture. Methodologically, we leverage remote sensing while integrating modeling, data assimilation, data science, decision-support, and water cycle science more broadly. Synthesizing input from the community questionnaire, the Water Demand Focus Area identified four overarching gaps (or, conversely, goals) within this topic: 1. Causes and drivers of evaporation and ET variations are not understood; 2. Natural water stores (primarily surface water and groundwater) are not sufficiently monitored to inform basin-level land management; 3. Consumptive use (human use) for water resource management is not known at the field scale; and, 4. Water and energy budget observations are not adequately understood to balance water supply vs. water demand (across scales). This white paper is an outcome of a community-led, community-engaged effort to elevate hydrologic science opportunities which would have significant benefit to support decision-making for drought, floods, water quality, water supply and water demand.</jats:p>