Enhancing Stream Forecast Modeling in California Mountain Watersheds

This study describes research using the NASA Ames version of the Carnegie-Ames-Stanford Approach (CASA) ecosystem model coupled with a surface hydrologic routing scheme called the Hydrological Routing Algorithm (HYDRA) to model the system of California watersheds. To assess CASA-HYDRA's ability to estimate actual water flows in both extreme and non-extreme precipitation years, we have compared the gridded model results on a monthly time scale with gage station data throughout the state. Considering the importance of the snow pack to the state's water regime, we are particularly interested in CASA-HYDRA's performance in California's mountain watersheds. Consequently, we made additional comparisons between our model and results generated from the USDA Snowmelt Runoff Model (SRM) applied to the Merced River watershed in Yosemite, CA. The results of both comparisons highlighted the need to enhance CASA-HYDRA's snowmelt algorithm. The efficacy of the degree-day approach has been demonstrated by the consistently solid performance of the SRM, so we have integrated this algorithm into CASA-HYDRA.