The objective of the symposium is to examine how ecological processes contribute to sustained water yield; how climate change, natural and anthropogenic disturbance have altered ecosystem water yield and water quality; and how these ecological processes and effects on water supplies vary among major regions of North America. The symposium will consist of a set of talks, each of which examines the trends in climate and hydrology at a long-term ecological research site and draws interpretations about ecological processes responsible for these trends and their implications for ecosystem management and water policy in the region where the long-term study is located. This symposium builds on two years of efforts to synthesize 20 to 60-year climate and hydrology records from long-term ecological research sites. Results from these analyses indicate that ecological processes including vegetation adaptations, disturbance, and succession strongly influence water yield and may overwhelm climate effects on water yield. The synthesis is based on records from the Long-Term Ecological Research Network, US Forest Service Experimental Forests and Ranges, USGS Water, Energy, and Biogeochemical Budgets program, USGS National Water Information Service, and Canadian long-term study sites. Each talk will focus on a particular region and its emblematic ecological and water policy issues, including novel analyses of long-term data.