PNNL

Abstract

Watersheds play a critical role in supplying water resources needed for hu-man use and ecosystem health. Understanding and predicting how, when, and where changes in the quantity and quality of water resources occur un-der di?erent environmental stresses including extreme events is crucial for sustainable management of water resources under a changing environment. However, few studies have attempted to quantify or identify the factors and process interactions controlling the impact of extreme events across water-shed systems. Only few large-scale studies include coordinated monitoring and modeling e?orts, which limits our ability to assess the large-scale im-pact of extreme events on water supply and quality. Methods are lacking to propagate uncertainty in process understanding through an integrated hydro-biogeochemical model framework and evaluate its importance, thus failing to take full advantage of the information potentially available through transfor-mative advances in characterization technologies from high-resolution mass spectrometry to airborne and satellite-based remote sensing. There are conse-quent risks to our nations water security and to human and ecosystem health that may become exacerbated with the increasing frequency of extreme events that is projected for the coming decades. This paper reviews the current sta-tus of watershed science for both water quantity and quality and identi?es critical gaps in our current knowledge and modeling capability in addressing the emergent needs in predicting watershed hydrologic and biogeochemical responses (i.e., water quantity and quality) under natural and anthropogenic perturbations. We highlight the need to (1) understand how environmental perturbations including extreme events like ?oods and droughts propagate through watershed systems and assess their short- and long-term impacts on watershed biogeochemistry, water quality and their recovery pathways; (2) develop and improve a watershed water quality model that re?ects the state of scienti?c understanding gained from observations; and (3) construct a data-model fusion system for watershed characterization, process identi?-cation, and mechanistic model parameterization. A large base of modeling, monitoring and data capabilities have been built by various federal govern-ment agencies given the relevance of water to their critical missions. An emerging need is to build an integrated national capability for watershed water availability and quality that can address water-related missions across multiple federal agencies.