Regional assessment of the trade-offs between environmental flows and human demands on river flows requires a hydrological framework which enables the consistent examination of the ecological response to more or less alteration of daily and other natural flow patterns. This framework is a comprehensive regional water management tool for integrating the flow needs of river ecosystems with human water needs. The PI developed an improved calibration strategy (the sequence of steps that one goes through in order to calibrate the model) and improved meteorological forcing data for the Variable Infiltration Capacity (VIC) hydrologic model to provide a more robust and extensive set of natural flows for assessing the ecological response to water management actions across the Colorado River Basin. The underlying data was then assessed the Yampa-White Basin to determine how the calibration can be extended to the rest of the Colorado River Basin. Streamflow data will soon be made available on a server. Future work will aim to (a) further develop the meteorological forcing data to better represent smaller scale variations in precipitation, (b) gather and assess the quality of naturalized streamflows, including the CBRFC daily quasi-natural flows, and (c) extend the calibration of VIC to the Upper Colorado basin.