Excerpt from A Climate-Change Scenario for the Columbia River Basin: Interior Columbia Basin Ecosystem Management Project: Scientific Assessment

This work describes the method used to generate a climate-change scenario for the Columbia River Basin Ecosystem Management Project, which began in 1993. The project required an estimate of potential climate change to complement various scenarios of management alternatives. The scenario considers climate patterns that may change if the atmospheric concentration of carbon dioxide (co2), or its greenhouse gas equivalent, were to double over pre-industrial Revolution values. Given the current rate of increase in atmospheric C02 concentration, doubling could occur within the next 50 to 100 years.

The Columbia River basin is in a transition climate zone between predominating maritime to the west, arctic to the north, and continental to the east. Consequently, it is difficult to characterize through means and averages. Therefore, many of the current stochastic methods for developing climate-change scenarios cannot directly apply to the basin. To circumvent this problem, a composite approach was taken to generate a climate scenario that considers knowledge of current regional climate controls, available output from general circulation and regional climate models, and observed changes in climate.

The resulting climate-change scenario suggests that precipitation could increase substantially during winter to +50 percent) and moderately during spring and autumn to +35 percent). A slight decrease (o to -5 percent) in summer precipitation is possible, except for the southeastern portions of the basin that may experience an increase in convective precipitation percent).

Low-elevation kilometer) temperatures throughout the year may increase 1 to 3 �c, with greatest increases during winter. This amount of temperature change is possible because of an expected loss of low-elevation snow cover. Warm temperatures and lack of low-elevation snow could reduce the magnitude of rain-on-snow floods. Wildfire potential could increase, however, as spring runoff from snowmelt is reduced. At high elevations, increased cloud cover could cause average temperatures to decrease during winter but be synchronized with possible warming at low elevations during summer. The diurnal range of temperature could decrease, especially in summer and autumn.

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