This working group addresses the question of how climate change and variability contribute to ecosystem water use, and how these changes may interact with succession and land cover change. Participants will discuss the question "How can we scale from point-based (i.e., meteorological station, eddy flux tower) measurements of water and energy fluxes to estimate ecosystem water use at the watershed or landscape and multi-year scales?” We will discuss recent published efforts, based on data from long-term ecological research sites, which combine measurements of temperature, precipitation, and streamflow to understand potential and actual evapotranspiration (e.g., using the Budyko curve), and we will evaluate how those estimates can be used to assess change over time in water use in response to climate change, land cover change, and ecological succession. The group will formulate a plan for continued intersite analysis of ecosystem water use and its responses to climate variability, succession, and land cover change at long-term ecological research sites.