Office of Columbia River photo identifier

Office of Columbia River

2016 Long-Term Water Supply and Demand Forecast

Download The Forecast

About The Forecast

Every five years, The Office of Columbia River submits an updated long-term water supply and demand forecast to the Legislature. The 2016 Forecast 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 2030s, 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 team will analyse 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.

Integrated Modeling

The forecast team integrate three modeling tools to develop the Forecast;

  • VIC (Variable Infiltration Capacity) - a land surface hydrology model.
  • CropSyst (Cropping Systems Simulation) - models crop use.
  • ColSym (Columbia River Simulator) - models reservoir operation.

The integrated computer model simulates instream supply and out-of-stream demands, accounting for climate, hydrology, irrigation demand, municipal demand, crop productivity, economics, existing water supply, and field calibration.

VIC and CropSyst were integrated for the first time, anywhere, in the 2011 Demand forecast. VIC informs CropSyst about daily weather and water supply. CropSyst informs VIC in the other direction with crop water needs and water stress levels.

Previous Forecasts

Legislative Directive

RCW 90.90.040
Columbia river water supply inventory — Long-term water supply and demand forecast.
(1)...the department of ecology shall ... develop a Columbia river water supply inventory and a long-term water supply and demand forecast...
(3) The department of ecology shall complete the first Columbia river long-term water supply and demand forecast by November 15, 2006, and shall update the report every five years thereafter.


Melissa Downes
Washington Department of Ecology
(509) 454-4259