Recent Improvements in Statistical Water Supply Forecasting in the Klamath Basin, Oregon

The Klamath Basin has had recent national focus for water supply issues in the West. This focus began in 2001, the 5th driest year since the early 1900s, which provided the backdrop of water supply shortages, pitting irrigation, fish, tribal needs and wildlife against each other in an effort to procure enough water for their competing needs. Since that time, efforts by the US Geological Survey and Natural Resources Conservation Service, supported by the Bureau of Reclamation, have improved the statistical forecasting techniques to increase water supply forecast accuracy. Recent changes have included using spring temperature, groundwater measurements and climate indices. The Trans-Niño Index is a new climate index that has improved the forecasts early in the season, where other climate indices are not well correlated. Spring temperatures provide a measure of snowpack conditions that drive runoff in the basin. The two groundwater parameters provide long term basin baseflow characteristics and recent climate effects on the groundwater resources that support surface water runoff in the spring and summer. These improvements have increased the accuracy of the water supply forecasting by 5 to 10 percent for the Upper Klamath Basin.