Using Seasonal Climate Forecasts to Improve Temperature Control Planning in Reservoirs and Streams
Water temperature management is an important factor in warm season operations at many of Reclamation's storage facilities. For example, the Mid-Pacific Region's Central Valley Operations Office (CVOO) uses water temperature models for Central Valley Project (CVP) rivers and reservoirs in order to assess the feasibility of stream temperature objectives. The Pacific Northwest (PN) Regional Office is developing similar models for application at Lake Roosevelt.
Current application of these models for planning water temperature management is based on the reoccurrence of historical weather conditions during the upcoming warm season. An alternative approach that appears feasible and is more defendable is to integrate seasonal climate forecasts into the model setup. This research would demonstrate integration and reveal decision benefits, focusing on the CVP as a case study. End-products include a tool for forecast data-handling and model setup assistance and a methods document to guide application in other regions.
Need and Benefit
Cold water release scheduling during summer and autumn months is a key factor in annual operations planning for many Reclamation projects. Cold water storage accumulates in reservoirs during the snowmelt season. Release of these cold assets allows Reclamation's to support fisheries' habitat during the warm season. A challenge with scheduling these releases is judging how much to allocate for supporting summer fisheries versus how much to reserve for supporting autumn fisheries. To improve planning capabilities, and thus decisions, Reclamation regional offices (e.g., MP and PN) have been investing in water temperature models to guide in-season negotiations with fisheries agencies. It is the goal of these negotiations to avoid conflicts related to how water and power operations might affect water temperature quality; further, to enhance fisheries health through better management of stream temperatures.
The CVOO procedures are representative of the state-of-practice within Reclamation. The process begins after CVOO staff have established monthly system targets for water deliveries and tributary storage. Stream temperature objectives for the various CVP tributaries are then used as a constraint, leading to schedule adjustments for the May-November period.
CVP stream temperature objectives are negotiated each year with Federal and State fisheries agencies. Objectives are formulated as: maintain temperatures below "x" at location "y" for various time periods throughout the warm season. Development of objectives depends on recently surveyed fisheries conditions, assumed cold water storage, and an analysis of simulated reservoir and river temperatures during the schedule horizon. The last step is iterative, as temperature management objectives are negotiated with fisheries agencies and adjusted several times--each instance requiring temperature simulation to assess feasibility.
The effectiveness of the schedule depends on subsequent weather and biological conditions. Even though operators can frequently adjust release conditions in the short-term (e.g., amount, depth of release), the cumulative effect of the release scheduling can only be assessed after the fact. One effect is that the cumulative summer release of cold storage comes at the expense of reserving less cold storage for autumn fisheries support. Balancing the summer and autumn cold water releases is a key consideration in Reclamation's goal of providing balanced support of temperature habitat for summer and autumn fisheries.
A key limitation of CVOO current procedure is assuming that warm-season weather conditions affecting stream temperature will be a reflection of historical conditions (i.e., sequence of daily median conditions during the simulation time period). CVOO does not currently consider expected climate during the upcoming warm season. It would seem to be beneficial, alternatively, to setup water temperature simulations with a weather sequence that is consistent with seasonal climate forecasts issued by either the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC), or the International Research Institute for Climate and Society (IRI). The CPC, for example, produces temperature and precipitation products in terms of:
* A single forecast for the upcoming month
* Twelve month ensemble of overlapping three-month forecasts.
Their forecasts are probabilistic, describing how likely any of the climatological terciles will occur during the upcoming time period.
Use of these forecasts would theoretically improve foresight of warm-season weather and water temperature conditions. This would translate into more effective temperature compliance objectives tailored for upcoming climate expectations. The end-result, ideally, would be reduced potential for conflict over Reclamation operations that affect fisheries habitat dependent on stream temperat
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