Potential Improvements to Colorado River Basin Forecast Center Water Supply Forecasts Using External Snow Products

The amount of water stored as mountain snow is the primary driver of seasonal (April through July) streamflow volumes in the Upper Colorado River and Eastern Great Basins. The Colorado Basin River Forecast Center (CBRFC) publishes seasonal, volumetric water supply forecasts starting in January for spring runoff volumes. CBRFC streamflow forecasts are used to provide impact-based decision support services throughout the region. The CBRFC continually seeks to improve their forecasts by incorporating new information into their hydrologic forecast system. To this end, the CBRFC is investigating the usability of external snow products in the current forecasting system. The CBRFC conducted an error attribution analysis to compare the uncertainties in April 1st water supply forecasts related to CBRFC hydrologic model errors and unknown future spring weather. Errors in model snow states are some portion of the larger model errors, along with errors from model soil moisture states, calibration parameters, model structure, etc. Results indicate that on average, roughly half of the forecast error in an April 1st water supply forecast is attributed to the unknown spring weather. It follows that improvements in model April 1st snow states can be expected to improve some portion of the other half of the April 1st forecast error.