Columbia River Basin Impacts Assessment: Update
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The Columbia River Basin Impacts Assessment is an activity of the West Wide Climate Risk Assessments (WWCRA), which is part of the Bureau of Reclamation’s (Reclamation) WaterSMART Basin Study Program (WaterSMART Program) established under the SECURE Water Act (2009). More information on the background of this legislation can be found in the first Quarterly Update.
Since the last Quarterly Update, Reclamation has been generating future climate change flows at specific locations throughout the Columbia River Basin. In addition, staff has been preparing the upper Snake River reservoir model to conduct operational modeling on the Snake River above Brownlee Reservoir.
Work is currently being done on a technical report to summarize methodology and results of the CRBIA. This includes the selection of climate change projections, development of future scenarios, and hydrologic modeling. The general finding thus far is increased temperature and increased annual precipitation (wetter winters, drier summers) in the basin, resulting in higher and earlier peak flows and lower summer flows for many locations across the CRBIA.
A comparison is being initiated with earlier climate change work, specifically the 2011 River Management Joint Operating Committee-I (RMJOC-I) study, which used Coupled Model Intercomparison Project Phase 3 (CMIP-3) projections. The CRBIA, which uses CMIP-5 runoff projections, will be compared to RMJOC-I runoff projections at several locations throughout the basin. Beyond finalizing reports and comparisons, the packaging and serving of the “future climate change flows” is being done for the CRBIA website.
Recently, the Upper Snake River MODSIM model was calibrated to current reservoir operations based on hydrologic year patterns, such as wet, dry, or average. Once the future climate change flows are completed, these datasets will be used to quantitatively evaluate the impacts associated with climate change on water delivery, power generation, ecological resources, flood control, and recreation at Reclamation facilities. Comparisons between historical flow and future flow windows will be made at specific locations throughout the upper Snake River basin and results reported (planned for December 2015).
Work is continuing on the methodologies and the technical memo is in progress. In the Columbia River Basin, several streams have a large component of flow supplied by groundwater (baseflow). Because climate change has the potential to impact groundwater supplies, streamflows may also be affected. Understanding the impacts of climate change on groundwater (baseflow) can help us to better understand the impact of climate change on overall water supply. This task includes identifying streams that have flow consisting mostly of baseflow in its natural, unregulated state, in an effort to better understand how climate change will fully impact streamflow.
Work is continuing on the methodologies and the technical memo is in progress. Water resource models, such as the Upper Snake River MODSIM model, are used to simulate the physical and human controlled processes that determine the movement of water through a regulated river system. The basic components of these models typically include reservoirs, diversions, and streamflow. The diversions represent water that is removed from the river, and the majority of that water is used for agriculture in the western United States. Historical diversions can be quantified by looking at actual diversion rates that are typically measured by various entities. As part of the Assessment, understanding how these diversion rates may change as a result of climate change can be problematic because the needs of the crops will change depending on the future temperature and precipitation conditions, and possibly the distribution of crop types and irrigated lands will change.
Staff is evaluating two possible methods to determine the future projected diversions rates using the upper Snake River MODSIM model. One method investigates adjusting various parameters associated with the irrigated lands (e.g., crop distribution) to calculate future evapotranspiration rates or ET. ET is essentially how much water is evaporated from a plant to air (evaporation) and how much water is lost from a plant as vapor (transpiration). Another method being considered is to adjust irrigation diversions by a change factor between historical and future ET values. Once a method is selected and confirmed, it will be documented.
Next Steps
Modeling is ongoing and there will more reservoir modeling results in the next quarterly update. A draft of the interim report for the CRBIA will be done by the next quarterly update in August.
Contact
Carri Hessman
Program Manager
(208) 378-5106
chessman@usbr.gov
Bureau of Reclamation
Pacific Northwest Regional Office
1150 North Curtis Road, Suite 100
Boise, Idaho 83706-1234
