Columbia River Basin Long-term Water Supply and Demand Forecast

Every five years, the Office of Columbia River submits an updated long-term water supply and demand forecast to the Legislature. The 2021 Columbia River Basin Long-term Water Supply and Demand Forecast (forecast) and the accompaning technical report were created through a partnership between Ecology, Washington State University, and the Washington Water Research Center. The report will help OCR strategically fund water supply projects by improving understanding of where additional water supply is most critically needed, now and in the future.

The forecast provides a generalized, system-wide assessment of how future environmental and economic conditions are likely to change water supply and demand by the 2040s, and is evaluated at three geographic tiers: the entire Columbia River basin, Eastern Washington’s watersheds, and Washington’s Columbia River mainstem.

Using state-of-the-art modeling techniques and economic scenarios, the forecast analyzes the impacts of climate change, regional and global economic conditions, and state-level water management actions on surface water supplies and irrigation demands across the Columbia River Basin.

The forecast finds that the availability of water to meet all instream and out-of-stream demands is vulnerable to expected changes in climate and population growth in Eastern Washington, even though the amounts of annual surface water supplies and agricultural water demands in the region are expected to be relatively stable.

Key findings in the forecast highlight the four main types of changes that are leading to vulnerabilities across Eastern Washington:

  • The timing of surface water supplies is shifting earlier in the season, especially in the snowmelt-dominated Cascades watersheds
  • Future changes in population and in agriculture in Eastern Washington could lead to increases in instream and out-of-stream demands for water
  • Groundwater levels are declining in most aquifer layers and groundwater subareas across Eastern Washington
  • Local increases in out-of-stream demands are expected, converging with local decreases in water supply, such as in the Yakima River Basin

We need to understand the nature of these expected changes in each watershed to help Washingtonians prepare for the future, and develop strategies to adapt and modernize water delivery infrastructure to address these vulnerabilities.

We're exploring approaches that can more directly leverage the power of our integrated modeling platform to inform a range of water management and policy decisions, helping Washingtonians evaluate how best to achieve their visions for a future that is resilient to a changing climate.

Data images from the forecast may be viewed at the forecast's data access site and are also available for download as a compressed file. A technical supplement for 2021 Columbia River Basin Long-term Water Supply and Demand Forecast will be available in mid-August.