Professor and Center Director Arizona State University
Evidence is mounting on the impacts of climate change on forested watersheds during the cold season. However, it is unclear how future warming conditions will interact with forest changes to impact streamflow yield to downstream users. In this study, we applied the TIN-based Real-time Integrated Basin Simulator (tRIBS) to watersheds of varying sizes in the Verde River of central Arizona to model the effects of warming conditions and managed forest treatments. Prior to developing the scenarios, we built confidence in the performance of the distributed hydrologic model through comparisons to observations from SNOTEL stations, streamflow gauging sites, and a spatially distributed snow water equivalent product spanning multiple years. The scenarios accounting for individual and combined changes in forest treatments and temperature focused on the effects to snow cover, evapotranspiration, and streamflow yield. The domain representation using triangulated irregular networks (TIN) allowed exploring two ways of representing forest treatments through fractional tree cover reductions in ~120 m pixels in the Beaver Creek case study and through individual tree removals of ~1 m pixels in the Sycamore Creek case study. Due to the strong orographic controls in the region, distributed hydrologic model performance was enhanced through the application of bias-correction and downscaling approaches for developing gridded meteorological forcing. For each case study, the climate and/or forest treatment change experiments yielded information on how annual streamflow and other water balance components changed at different levels of warming and for different levels of forest thinning. Study findings were presented to water managers using summary graphics that allowed for ease of interpretation despite the complexity of the underlying simulations. Overall, forest treatments in the Verde River study areas are expected to offset warming impacts on streamflow yield up to certain thresholds dependent the thinning level and temperature increases.
