Application of a Physically-Based Distributed Snowmelt Model in Support of Reservoir Operations and Water Management
This project will focus on Reclamation's need for hydrologic modeling tools that can optimize reservoir management decisions to improve planning and management of water supplies.
We will apply the latest advances in snow accumulation and melt modeling to the Boise River Basin, which contributes inflows to three reservoirs. This will be the first application of a physically-based distributed snow model in an operational forecasting setting. Are these modeling techniques appropriate to operational needs and do the deliverable products improve reservoir management outcomes?
Need and Benefit
Current operational snowmelt-driven streamflow forecasts are derived from statistical relationships largely based on a combination of historic trends and calibrations to point observations of SWE or as-available satellite observations of snow-covered-area. These models rarely contain a physical basis. It has been shown that these models become unreliable when non-normal conditions are encountered.
Physically-based, distributed models require little to no calibration and are based on current and predicted conditions. The physical basis means that all mass and energy fluxes that affect the snowcover are numerically calculated based on the governing physics. These models are robust to non-normal climate conditions and ideal tools for evaluating streamflow responses to short-term extreme events such as rain-on-snow, the extended effects of unseasonable wet, dry, warm, or cold periods, and the long-term effects of climate warming.
Up until now the reasoning has been that the computational demands of modeling over large basins required simpler, parameterized models. A lack of driving data (i.e. mountain weather observations) for physically-based modeling has also been seen as an impediment to more complex solutions. Today however, computational capabilities have multiplied, efficient techniques for distributing limited observations have been developed, and gridded weather forecasts are readily available.
The proposed work will provide immediate benefits to Reclamation. Current maps of basin-wide SWE will answer the oft-asked questions, "How much snow is still up there and where is it?", "Where is the snow located?", "When will the snow come off, with the next warm spell, rain storm, etc.?" The up-to-date maps of snowcover cold content will provide managers data on how sensitive reservoir inflows will be to subsequent energy inputs. Upon completion, the potential role of physically-based snow modeling in the realm of operational river forecasting will be known. The physically-based foundations of these modeling tools will be directly applicable to basins throughout the region – basin-specific calibrations are not necessary. If successful, reservoir managers will have an advanced, modern tool for predicting inflows, optimizing water usage, and increasing flood protection.
The immediate benefit of this proposal is to the PN Region. However, a pilot study was completed in a small California watershed in 2008. If techniques can be effectively scaled for a large river basin like the Boise, they could be effective in any snow driven basin in the Western US.
In all three years, up-to-date maps of modeled SWE and snowcover cold content will be delivered to the Bureau of Reclamation's Pacific Northwest, Boise office. Weekly maps will be routinely produced throughout the snow season and at finer timescales on an as-needed basis. In the final year, short-term (1 – 3 day) forecasts of reservoir inflows will be provided on an as-needed basis.
Annual reports will assess the accuracy of simulated snow patterns compared to satellite-retrieved observations (years 1 – 3), simulated runoff to observations (years 2 – 3), and forecasted runoff to other forecast products and observations (year 3). The final report will deliver conclusions on the usefulness and value of physically-based snow modeling in operational river forecasting along with guidance for future development.
All collected data will be archived at the USDA-ARS Northwest Watershed Research Center in Boise, ID and made available to the Bureau of Reclamation. We also anticipate sev