Regional hydroclimatic impacts of a warmer climate in the central Rocky Mountain headwaters region

Assessment of potential climate change impacts on seasonal water and energy budgets over the central and southern Rocky Mountains is challenged by the presence of highly complex orography and variability in land surface hydrologic conditions. The large magnitude of topographic gradients expressed over small distances necessitates the need for high resolution models in order to properly simulate the dynamics of cold and warm season precipitation events. Results from high-resolution (4km) regional climate model time-slice experiments over the central and southern Rocky Mountains are presented in the context of understanding the change in land surface and atmospheric water budgets. Water budget analyses from the high resolution model are contrasted with those from the parent global model from which a component of the regional model forcing was derived. It is shown that not only does the regional model produce different magnitudes of change in current and future water budgets than the global model but that there are distinct changes in the seasonality and, at times, the sign of the annual changes. The changes over the regional scale using the regional model are then mapped according to headwater river basins ranging in spatial scale from a few hundred km^2 to 10,000's of km^2. The results of the river basin scale analyses show periods of significant potential for future water resource stress in seasonal water budget change patterns produced by the regional model. The physical mechanisms behind these change patterns are discussed in the context of their uncertainty and relationship to the experimental design.