Work: Annual and Seasonal Flow Trends

To allow for the most detailed analysis possible, the trend analysis was based on a 30-year time period (1971-2000). In order to confirm if the 1971-2000 period results in different trends than other time periods, the 1971-2000 trends were compared to trends covering the periods of 1912-2001, 1951-1980, 1961-1990, and 1970-2008.

From the trend comparison analysis it can be concluded that the application of the 1971-2000 period for trend analysis does not generally result in extremely negative trends, and rarely results in the highest positive trend. On the contrary, and especially in southern Alberta, the use of the 1971-2000 period results in rather too positive trends, especially when compared to longer time periods. Therefore, using the 1971-2000 trends can be interpreted as resulting in either average or under-estimating trends. Therefore, reported trends are more likely to be more negative than the long-term trends.

 

Summary of Alberta Streamflow Trends (1971 to 2000)

Out of 102 watersheds for which trend analyses could be carried out, 60 had negative trends in mean annual streamflow. 14 watersheds had a negative streamflow of over 1% per year, which means that after 10 years, over 10% less streamflow would be available if the detected trends were to continue.

 

Annual Streamflows

water-yield-map2

The mean annual flow is declining in southern Alberta (Oldman, Milk, lower Bow) as well as northern Alberta (lower North Saskatchewan, Athabasca, Peace) and increasing in western-central Alberta (upper Bow, Red Deer, upper North Saskatchewan). However, the only watersheds that exhibit highly significant trends are the Athabasca and the Churchill Rivers, both with the strongest negative trends, and the central Peace River.

 

alberta trend min annual flow2Minimum Annual Flows

As minimum flows are more sensitive to environmental changes, the trends are stronger in magnitude (both negative and positive trends). The spatial pattern across Alberta is not as clear as the mean annual trends, with many major watersheds having both strong positive and strong negative trends, most of which are also highly significant. Again, the Athabasca and Churchill Rivers stand out as rivers which have strong negative trends.

 

alberta trend max annual flow2Maximum Annual Flows

The spatial pattern of the maximum annual flow is quite similar to the mean annual flow, with the Red Deer River having the strongest increase in maximum flows.

However, with the exception of the Peace River and the Churchill River, most maximum annual flow trends are not significant.

 

Seasonal Streamflows

awri trend-percent-of-mean-winter-q2Winter Flows

With few exceptions, such as large parts of the Athabasca River and the Churchill River, winter flows are increasing.

This can be explained by the recent increase in rainfall during winter, which is not stored, such as snow, and can run off to become streamflow.

 

awri trend-percent-of-mean-spring-q2Spring Flows

Spring flows are declining in southern Alberta, with the exception of the St. Mary watershed, which contributes about one quarter of the streamflow in the Oldman River watershed. Some headwaters in the Bow, as well as the upper North Saskatchewan River and most of the Peace River show an increase in spring streamflow. The Athabasca River and the Churchill River show a strong decline in spring streamflows.

awri trend-percent-of-mean-summer-q2Summer Flows

The spatial pattern across Alberta of summer flows is quite similar to the mean annual flow. Central Alberta exhibits increasing flows (central Bow, Red Deer, North Saskatchewan, upper Athabasca), while the rest is showing declining trends. Other than in some northern watersheds, most trends have a significance level of under 80%.

 

awri trend-percent-of-mean-fall-q2Autumn Flows

With few exceptions, the autumn streamflow trends are quite similar to the summer streamflow trends.

 

 

Work: Alberta's Water Yield

Water Yield can be calculated by dividing the mean annual volume of streamflow that is produced in a nested watershed (expressed in cubic meters per year), by the area of the nested watershed (expressed in square kilometers).

 

Water Yield =

Mean annual volume of streamflow (produced in a nested watershed)
Area of the nested watershed

 

The area of a nested watershed can be determined using the following approach:

nestedarea

    • The watershed associated with Station 1 (orange area in the Figure on the left) has a nested area of 15 km2 and a gross area of 15 km2 (they are the same, as no further upstream watershed exists).

 

  • The watershed associated with Station 2 (green area in the Figure on the left) has a nested area of 10 km2 and a gross area of 25 km2 (sum of this green watershed and the upstream orange watershed).

The water yield can also be expressed in mm, as both precipitation and evaporation are typically expressed in mm. For example, a watershed with 1,000 mm annual precipitation, and an annual 40%, (i.e. 400 mm), water loss due to evaporation, would have a water yield of 600 mm per year.

A total of 287 watersheds in Alberta were analyzed for water yield. The water yields vary from negative values in 12 prairie watersheds, where more water enters the watershed than is flowing out (this is possible due to evaporation losses within the watershed), to values of over half a million m3 per km2 per year in 21 high altitude Rocky Mountain watersheds. The water yield in Alberta has a distinct spatial distribution, with three major areas.

Water-Yield-Map

  • The highest yields, over 300,000 cubic meters (per square kilometer per year), reflected as the dark blue regions on the map, are produced in the Rocky Mountains. Within the Rocky Mountains, Alberta’s south-west corner has the highest yields (also including the St. Mary’s watershed, which has its headwaters and highest yields in Montana of 640,000 cubic meters (per square kilometer per year). These high-yielding watersheds produce, on average, over half a million cubic meters (per square kilometer per year).
  • The lowest water yields are produced in the prairies, reflected as the dark red regions on the map, where the combined effects of low annual precipitation and high evaporation losses result in very low (under 25,000 cubic meters (per square kilometer per year), and occasionally negative, water yields, averaging just under 10,000 cubic meters (per square kilometer per year).
  • The third region is the in-between region, reflected as the yellow-gold regions on the map, and found mainly in central and northern Alberta (as well as between the high-yield and low-yield regions). Here, water yields range from 25,000-300,000 cubic meters (per square kilometer per year), with an average of just over 100,000 cubic meters (per square kilometer per year).

 

Summary of Water Yield analysis based on 287 watersheds across Alberta

 

Water Yield
(m3 per km2 per year)

Water Yield
(millimeters)

Number of watersheds

Average

137,000

137

-

Minimum

-35,000

-35

-

Maximum

1,084,000

1,084

-

Median

64,000

64

-

Low yield

>25,000

>25

83

Medium yield

25,000 – 300,000

25 - 300

164

High yield

>300,000

>300

40 

Percent Contribution of Major Watersheds

WaterYieldOverallPercent

The second map shows what proportion of water yield within each of the major watersheds is produced where. This map is useful for water managers, as it provides insight into which are the most water producing watersheds.

The percent water yield is calculated by dividing the water yield of a nested watershed by the water yield at the outlet of a major watershed (eg: Bow River) and multiplying by 100. For example, if the watershed at Station 1 has an annual water yield of 3 million cubic meters, and the water yield at the outlet at Station 2 is 4 million cubic meters, then the percentage contribution of Watershed 1 is 75%. Assuming the same annual water yield (expressed in cubic meters per square kilometer), the larger the watershed, the higher its relative contribution.

The reader must bear in mind that the percentage (colour) is dependent on the size of the watershed. For example, where two neighbouring watersheds have the same water yield per km2, the larger watershed would have a higher proportion of water contribution. For example, during 1971 - 2000, almost 33% of all water flowing out of the Bow River at the confluence with the Oldman River is produced by two small sub-watersheds upstream of Banff, while another approximately 45% is produced in the other Rocky Mountain and adjacent foothill sub-watersheds. The entire lower half of the Bow River watersheds produces only, on average, 3% of the streamflow.

Work: Water Yield and Streamflow Trend Analysis for Alberta's Watersheds

Alberta is a province with a very diverse climate. The consequence is that some watersheds capture large amounts of water for downstream users, while other watersheds capture almost no water.

Agriculture, energy, and economic development over the last century has transformed Alberta. Water often remains a significant limiting factor to population growth, economic development and environmental protection. Whether one considers irrigation, tourism, recreation, or the economic development in urban and rural areas, water remains the key to unlocking new opportunities. When we dd in the uncertainties  associated with climate change, it is clear that an inventory of current water resources is the first step towards prudent water resources management.

alberta-water-yield-map2

Though there is considerable spatial agro-hydrological information available on watersheds, soils, and land suitability for Canada (National Land and Water Information Service) and the prairies (Agri-Environment Services Branch), many important hydro-climatological variables are not available at a provincial or regional scale.

Efforts to develop an inventory of Alberta's current water resources (Alberta Hydro-Climatological Atlas) have been significantly advanced by the research of Dr. Stefan Kienzle (Associate Professor, Dept. of Geography) at the University of Lethbridge, with funding and support from the Alberta Water Research Institute (now Alberta Innovates Energy and Environment Solutions), and Alberta Innovates Technology Futures.

Dr. Kienzle's report titled Water Yield and Streamflow Trend Analysis for Alberta Watersheds provides a comprehensive analysis of Alberta's streamflow records (from 1971 to 2000) for both magnitude and possible trends.

 

We encourage you to learn more about this research and Alberta's water yield, and its river and streamflow trends, by clicking the links below:

Alberta's Water Yield

  • Cubic Meters (per square kilometer per year
  • Percent Contribution (for major Alberta watersheds)

Annual and Seasonal Flow Trends

  • Annual Flows (mean, min, max.)
  • Seasonal Flows (winter, spring, summer, fall)

 

Contact us, if you have a question for Stefan Kienzle on the report Water Yield and Streamflow Trend Analysis for Alberta Watersheds.