Recently observed temperature data suggests that areas of Alberta have warmed slightly over the past 50 years, as measured by average annual temperature. The last 20 years seem to show much of this increase is due to higher minimum temperatures and warmer winters. However, the global climate system is extremely complex and temperature information alone cannot explain what the possible effects of climate change might mean for Alberta. Because the components of the hydrologic cycle are all interrelated, feedback from one component (for example, temperature) leads to changes in other processes (evaporation, precipitation) - leading to further changes (streamflows and runoff, groundwater recharge and discharge)... and so on.

It has been suggested that increased temperatures could 'accelerate' the hydrologic cycle, meaning that increased precipitation and increased evaporation would be expected. However, whether or not this would cause less (or more) runoff and streamflow in our rivers depends upon the relative amount of change between the two variables. Also, if more rainfall (but less snowfall) resulted from higher temperatures, it is possible that reduced streamflow in the plains and prairie areas could occur even if overall annual precipitation totals increased. This is because the annual spring runoff and snowmelt provides such a significant contribution to the annual water balance. Due to the complexity and interdependence of the variables, and combined with the complexity and uncertainty of modeling global weather patterns, determining the possible effects of climate change for Alberta is very difficult. Therefore, much of our climate change knowledge is still based on measured data and observations.

Climate records for precipitation in Alberta are about the same in length as for temperature - generally less than 100 years in most places. Precipitation and its variability have been discussed in the climate data web page. An analysis of annual precipitation totals at nine stations in Alberta indicates that no clear trend has been identified. This means that the average precipitation does not seem to be changing much, although it appears that the variability one year to the next may be decreasing. Alberta has experienced a series of dry years, although these seem to be within the range of historical patterns. A test for seasonal patterns still needs to be undertaken to see if winter snowfall and summer rainfall averages have changed over time.

Alberta Environment has examined historical streamflows in nine major rivers. There has been concern about recent dry conditions throughout the Province. The analysis indicates that these conditions seem to fit within the range that we have observed historically. Although the possibility of climate change cannot be ruled out, the study did not identify a clear or consistent pattern of significant decline in natural annual streamflow volumes over the past 90 years - the longest period where data is available. Perception of declining river flows is likely driven by two factors: first, increasing net consumption of water, which results in lower-than-natural river flows; and second, from flow regulation, reducing variability in flows thereby leading to observations of lower flows during traditionally higher-flow periods. Sample plots of historical recorded annual streamflow volumes for two rivers are shown below, representing one southern river (Bow at Calgary) and one northern river (Athabasca at Athabasca).

	Bow River at Calgary				Athabasca River at Athabasca

You can download the entire report Trends in Historical Annual Flows for Major Rivers in Alberta from the Information Centre. The report is 1.9 MB in size and has been posted in Adobe Postscript (.pdf) format. You will require the Adobe Acrobat Viewer, which can be downloaded for free from Adobe Systems Inc.

Although it is not yet clear whether a long-term decline in streamflows may be occurring in Alberta, the wise and efficient use of water is becoming increasingly important. Both higher water diversions for consumptive uses, and potential effects due to climate change, can have the same net effect on water supply in that the amount of water available in lakes and rivers has been reduced. Drought can occur almost anywhere in the Province and can have relatively short-term but significant impacts on water supplies. In addition, allocations of water in some areas (particularly in the south) have nearly reached the limit of available supply, requiring more efficient use of the existing resource in order to support a growing population and economy. Refer to the provincial Water Strategy for more information on the steps that Alberta is taking to ensure that water is wisely managed for the future.