State Water Resources Research Institute Program

Project ID: 2008ID99B
Title: Climate Change Impacts on the Snake River Plain's Surface & Ground Water Resources
Project Type: Research
Start Date: 3/01/2008
End Date: 2/28/2010
Congressional District: First
Focus Categories: Climatological Processes, Surface Water, Groundwater
Keywords: Snowmelt Runoff Modeling, Climate Change Scenario, Water Distribution, Doctrine of Prior Appropriations, Agriculture, Irrigation, Evapotranspiration, Groundwater Recharge
Principal Investigator: Qualls, Russell J.
Federal Funds: $ 20,000
Non-Federal Matching Funds: $ 40,000
Abstract: Over 3 million acres of farmland are irrigated across the Snake River Plain in southern Idaho. The Snake River Plain encompasses about one-half of the irrigated acreage in the Pacific Northwest. Irrigation demands total some 12 million AF of diversions, and are quite stable from year to year. Irrigated agriculture occupies a significant fraction of the region's economy. Climate change is likely to manifest itself most significantly in changes to the region's water supply. Irrigated agriculture therefore may be one of the region?s most vulnerable economic sectors to the impacts of climate change.

More than half of the water supply for the Snake River Plain has its source in the mountains on the eastern edge of the Snake River Plain. Therefore, previous and proposed snowmelt runoff research focuses on the Upper Snake River, which has also been listed in the "highest priority" category for snowmelt runoff modeling by IDWR.

The impact of climate change on southern Idaho water supplies has begun to be investigated by coupling a snowmelt runoff model (SRM) with a basin wide model of reservoir operations and prior-appropriation water allocation (MODSIM). Previous work determined only the average annual impacts of selected climate scenarios, however, this does not address the degree of inter-annual variability which will still exist within an altered climate. In particular, within the range of variability which will occur, it is the extremely wet or dry conditions which will likely be the most problematic (in the case of drought years) or the most beneficial (in the case of the wet end of the extreme). The work proposed here will focus on the inter-annual variability as well as the variability in the timing of spring runoff and its distribution throughout the highly managed Snake River Plain for both the historical surface water flows as well as the impacts of six climate change scenarios corresponding to wet, average and dry climate scenarios for two different time periods, one approximately 25 years and the other approximately 75 years into the future. The climate scenarios were taken from model output included in the IPCC Fourth Assessment Report (AR4) for the mid-range (A1B) carbon emissions scenario.

MODSIM was used to simulate reservoir operation and prior-appropriation doctrine water allocation given the mean condition hydrologic water supply from SRM. MODSIM model results included both the average and time-distribution of expected irrigation water shortages by river reach and tributary within the Snake River Basin. However, as with the previous SRM work completed by the PI, the MODSIM results only address climate change impacts associated with the mean water supply. We propose to use the results from the SRM work proposed above to evaluate the effects of climate change on the distribution of water using MODSIM for the extreme (wet or dry) characteristic conditions from each climate scenario, as this work is likely to reveal most clearly the shortcomings of the existing infrastructure and water rights.

Finally, I propose to assess the impacts of climate change on irrigation demand by calculating the changes to evapotranspiration over the irrigated land of the Snake River Plain corresponding to each climate change scenario.

Progress/Completion Report, PDF

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