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Generalized Stream Flow Depletions Model for Historic and Projected Future Climate Scenarios

Project ID: 8013
Principal Investigator: Christopher Murray
Research Topic: Water Supply Forecasting
Priority Area Assignments: 2014 (Climate Change and Variability Research)
Funded Fiscal Years: 2014
Keywords: streamflow, hydrologic model, depletions, crop water use, consumptive use, water balance, efficiency

Research Question

For water managers, having good stream flow depletion data is critical to keeping accurate water balance equations to inform the allocation decision process. Water managers are often forced to compare face-values from water right permits and try to infer what the actual depletion rate is, given that information. The Great Plains Region (GP) has dealt with this issue in the Missouri River Basin by developing a model, which calculates the stream depletions, by reach, using actual irrigated acres and crop water requirement calculations. The crop water requirements are then used to produce the reach depletions attributable to agricultural diversions. GP has been improving this model for the past two decades, and currently has an adequate model of the Missouri River Basin. However, since the original development of the model, a number of factors have resulted in a need for model upgrade. First, the equations used in the model do not reflect the state of the art in crop coefficient calculations. Secondly, climate change has become a large part of the planning process. Thirdly, GP has realized this model could be generalized to work in other basins. Fourth, considerable interest in the model from outside agencies has been observed, indicating this model could be very beneficial to a much wider audience. Fifth, the personnel that developed the model have retired and their specialized knowledge is no longer available. Therefore, GP wishes to scope a project to update, upgrade, generalize, and distribute this model so that it can be used for processing historical depletions and global climate model (GCM) outputs to analyze the changes in stream flow depletions resulting from modeled climate scenarios and historical water use. This would further water rights planning, instream flow planning for fish and wildlife, yield analyses for reservoirs, water availability analyses, and other resource planning efforts under both current conditions, and under climate change conditions.

Need and Benefit

The Missouri River Basin Depletions Database Model (Model) has been used by the Bureau of Reclamation to support various large scale studies of water use and water allocation. The most recent use was to supply the Corps of Engineers (COE) a basin-wide depletion dataset to support their firm yield analysis of the six COE main stem reservoirs on the Missouri River. This dataset provides a complete water balance picture for water managers who must compare "unimpaired" or "pre-project" flows with current or "post project" flows. These comparisons have many uses in terms of understanding water rights, fish and wildlife flows, water availability, project operating efficiency, and their associated impacts. The Model has been incredibly useful as needed and when used. We want to make the model more useful by extending the capabilities and analyses performed by the Model (by adding climate change scenarios) and extending the geographical scope of the Model to other basins where agricultural use is prevalent. This revision to the model would provide a linkage between climate change, crop consumptive use, and stream flow depletions.

The Model uses the Blaney-Criddle and Jensen-Haise methods to calculate the crop water requirements for the basin. These methods are considered outdated, and Reclamation has provided funding to Desert Research Institute to provide a Penman-Monteith model to be used on Reclamation projects. Penman-Monteith provides crop water use, but does not take the next step to calculate the return flows that make their way back to the stream, resulting in the calculated actual stream depletions. This project is envisioned to fill in some of the gaps in the way agricultural water use is analyzed. The depletion calculation methods that exist in the Model can be conjoined with the previously developed Penman-Monteith method, to produce a modernized tool that can be extended for use in other areas. There is nothing inherent in the Penman-Monteith method or the depletion calculations that is specific to the Missouri Basin, other than the input data. For this reason, we intend to take a hard look at input data and determine the best sources and methods for obtaining input data for the Model. With the development of modern climate models, there has been a corresponding improvement in access to climate data in general. One of the purposes of this project will be to take advantage of the available climate data and climate model outputs to feed into the stream depletion model, to complete the cycle from climate change to crop impacts to streamflow impacts. The resultant dataset from such an analysis would be highly useful as input to any of the widely used hydrologic models for more specific analyses, supporting any type of water supply planning studies that are performed, at a very useful spatial scale. The model products would support yield analyses, water rights analyses, water availability studies, instream flow studies, reallocation studies, habitat studies, and more, helping water managers maximize the beneficial use of the limited supplies.

Research Products

This proposed project will result in developing:

• A review of current methods and data sources that can be used to enhance the capabilities of the Model.

• A scope of work detailing tasks, roles/responsibilities, schedule, and budget for improvement of the streamflow depletion tool, including phasing of future work and expanding the model to other areas of the US.

This information was last updated on September 2, 2014
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