Seasonal Climate Forecasts for Water Temperature projections in Reservoirs and Streams
* Can we use seasonal climate forecasts to better inform forecasts of reservoir and stream temperatures and their expected limitation on Summer-Autumn reservoir operations?
Summer and autumn aquatic temperatures have become important controls on water and power operations in Reclamation's Mid-Pacific (MP) and Pacific Northwest (PN) regions. Some system operators use daily simulations of aquatic temperatures to produce information on these anticipated controls during planning. However, current application of these temperature simulations is based on weather from a reference year and not on any anticipated climate during the planning horizon. This research proposes to scope a project that better informs the climate assumptions of these simulations, either by using National Oceanic and Atmospheric Administration's (NOAA) existing climate forecast products or by using teleconnections-based forecasting technology. Methods developed in this effort would benefit other Reclamation regions where aquatic temperatures are a consideration in operations planning.
Need and Benefit
Reclamation's water and power operations in MP and PN regions are becoming increasingly sensitive to summer and autumn aquatic temperatures in streams below project reservoirs. Planned management of cold water resources in these reservoirs is a key component to adequately managing stream temperature conditions and avoiding habitat-related conflicts that might impair water deliveries and power generation.
Operations planning for stream temperature management is an evolving process in both regions. Planning is most evolved in the MP's Central Valley Project (CVP) where summer release schedules, developed initially for water deliveries and storage conservation, are adjusted for stream-temperature management during the warm season (around July through October). These schedules are issued initially in May, and are updated monthly leading into the autumn months. Separate schedules are issued for CVP tributary systems (i.e., the American and Sacramento Rivers below Folsom Lake and Lake Shasta, respectively). Compared to planning process in the MP CVP, PN operations planning for stream temperature management is in a more formative stage. Current activities involve planning the development of reservoir and river temperature simulations for Lake Roosevelt and the main stem Columbia River below Grand Coulee Dam. It is envisioned that these simulations will be used to support seasonal operations planning.
In these applications to support seasonal operations planning, reservoir and river temperature models are used to simulate aquatic temperature conditions during the multi-season planning horizon. These models compute temperatures at a daily time-step based on input hydrology, inflow temperature, weather, and physical system characteristics. Daily weather inputs include: air temperature, dew point temperature, net radiation, precipitation, and wind. Simulation outputs include: reservoir mixing conditions, reservoir temperature conditions at depth, reservoir release temperatures, and river temperatures at downstream locations.
A limitation on model use is the assumed weather and inflow temperature during the simulation. Current assumptions in the MP CVP application do not involve any climate forecasting. Instead, simulations for the MP CVP application rely on assumptions set equal to observations from a reference year or set of years.
This research addresses the limitation by scoping a project to demonstrate how to condition assumed daily weather and inflow temperature inputs based on seasonal climate forecasts. Several questions would be addressed during scoping:
* Which climate forecast products should be used? (e.g., products from NOAA's Climate Prediction Center [CPC] or experimental forecasts developed using teleconnections-based technology, relating Pacific Basin climate patterns to simulation-season weather conditions)
* How should the climate forecast products be related to the daily weather inputs for reservoir/river temperature simulation? (e.g., using the climate forecasts to guide selection of "like-year(s)" among historically observed weather years; or, using the climate forecasts to guide perturbation of daily weather time series from a reference year or set of years)
* What demonstration would be required to introduce the technology into operations?
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