Climate Change and Extremes in the Canadian Columbia Basin

A brief summary of the first regional analysis of projected changes in extremes for the Canadian Columbia Basin is presented. The study makes use of an ensemble of eight Regional Climate Model simulations from the North American Regional Climate Change Assessment Program. First, the regional models' historical simulations are compared with their coarse-scale driving data as well as with gridded observations. This analysis indicates that the regional models generally improve upon their coarse-resolution forcing, particularly for precipitation. By the middle of the twenty-first century, annual mean temperature in the basin is projected to increase by 1.8 degrees C to 2.7 degrees C compared with the past (1971-2000). A 1% to 9% increase in annual total precipitation is projected. These projections are compared with a wider range of projected changes from a larger ensemble of coarse-scale global climate models. The projected changes to extremes that accompany these changes in mean conditions are considerable. Warm days in summer are projected to occur 1.5 to 3.3 times as often as in the past. Extreme warm days (defined as 25-year return period events appropriate to the reference period) are projected to occur 1.4 to 12.5 times as often as in the past. Cold extremes are correspondingly projected to decrease in frequency or cease altogether. Projected increases in precipitation during very wet days are similar to the overall annual precipitation increase. The frequency of extreme wet days (25-year return period events) is projected to be between 0.3 and 4.1 times the frequency in the past.