Climate Change

Climate Change Conditions

The impact of climate change is best understood by comparing conditions in a known historical period with conditions that have been modelled for some comparable future period. By convention climate normals are calculated every ten years from the previous 3 decades observations. The current climate normals are based on the years 1961-1990. Climate change comparisons such as the ones here are often made between the normal period 1961-1990 and the future periods 2010-2039 referenced as 2020s, 2040-2069 referenced as 2050s and 2070-2099 referenced as 2080s. 

Driving the flow model with weather derived from climate change models predicts dramatic changes in the flow of the Fraser River. While the total flow remains relatively constant the character of the flow changes significantly as shown by lower and earlier peaks as the century progresses.

The temperature model predicts significant changes in the Fraser River temperatures when it is driven by weather from the climate change models. By the end of this century, throughout all of July and August, the average daily temperature will exceed the highest average daily temperature (see dashed line) that was observed during the normal period.

Impact of Climate Change on the Fraser River

In the temperate zone, rivers are characterized as having either snow melt dominated flow or rainfall dominated flow. The Fraser River is a typical snow melt dominated river with low winter flow, a sharp spring increase in flow with a late spring peak followed by a gradual decline throughout the summer and fall. During the last 30 years of this century the models show that climate change may cause the Fraser River to become rainfall dominated in some years with the peak flows occurring as a result of heavy summer and fall rainfall events.

Temperature conditions for each year in the normal period (1961-1990) were examined to determine the year that was most detrimental to salmon spawning success. Conditions for this year were compared to the temperature conditions that salmon could be expected; to encounter in the future with climate change. By the end of the century it is expected that at least every second year will have conditions that are more detrimental to spawning than the worst year in the normal period.