The Role of Vegetation in Past and Future Global Hydroclimatic Change

Plants influence how energy and water move in and out of the land surface, and this affects how much freshwater is available for human consumption. As carbon dioxide concentrations increase, temperatures warm, and precipitation patterns shift, it is crucial to understand how plants will respond in order to plan for future changes in fresh water availability. This project will work to understand how and why vegetation changes with climate, assess the performance of land-surface models that simulate these processes, and evaluate how well these models may represent future risks associated with freshwater availability, such as changes in drought or long-term aridity. We will perform a model-by-model evaluation of the state-of-the-art collection of Earth System Models (known as the Coupled Model Intercomparison Project, or CMIP6, class of models), with a heightened focus on the Department of Energy's E3SM model. We will seek to understand how representations of vegetation within these models influence simulations of freshwater availability, with a specific focus on droughts defined by soil moisture and runoff. Three questions will drive our research: (1) how do errors in how vegetation is modeled impose inaccuracies in how past droughts are simulated?; (2) how do these errors affect assessments of future drought risks as atmospheric concentrations of carbon dioxide continue to rise?; and (3) where should model development focus to improve representations of vegetation and reduce uncertainties in projections of freshwater availability? Our approach will translate projections of freshwater availability and their uncertainties into risk assessments that will be relevant for stakeholders and decision makers.