Farmers cannot change the weather but they can make better use of what naturally comes their way.
Capturing snow can increase surface moisture or help avoid excess runoff for the often dry Prairies, without a need for more dams and irrigation, said John Pomeroy of the University of Saskatchewan.
The book Snow Cover, co-written by Pomeroy and Don Gray, suggested that farmers can get an extra four kilograms per acre of spring wheat yield for every extra millimetre of water (four bushels of spring wheat per acre for every inch of rain) from the melt of a snowpack.
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The snow water equivalent, or SWE, used to convert the water from snow to units of rainfall is the equivalent depth of water over a unit of land that would result if a snowpack was melted.
Pomeroy explained that 10 mm of rainfall is the same as 10 mm SWE in terms of the water delivery to the ground. He said 10 mm SWE could be a snow depth of two to 20 centimetres.
On a broader scale of drought-proofing, Lake Diefenbaker in Saskatchewan is a good resource that can store water from one season to the next.
It has not been fully used, said Pomeroy, who expects irrigation from the lake to be expanded for areas with high heat units where high value crops are possible. He noted the example of southern Alberta, where sugar beets and feedlot industries have flourished on the irrigated lands.
Although not designed principally for flood protection, Lake Diefenbaker has also played a role in protecting municipalities from rising waters resulting from heavy rains in Alberta, especially this spring and summer. Dams in Alberta also mitigated flood damage.
Climate change, global warming and extremes of weather could alter prairie weather and precipitation in the coming centuries.
The average annual precipitation received throughout much of the Prairies is 300 to 380 mm, with snow accounting for 39 percent of that amount.
In one scenario, the Prairies could see more precipitation in the form of snow each year and in-field snow management could become more important to retain moisture across the fields, said Pomeroy.
“About 30 to 40 percent of winter snowfall evaporates off on a summerfallow field,” he said, adding much snow also evaporates in a snowstorm.
Water drainage into the soil can be increased by as much as 40 percent under continuous cropping-minimum tillage systems. At the same time, the runoff from fields is decreased by 25 percent.
That means fewer sloughs, dugouts and streams for farmers relying on that water resource.
He cited the impact that minimum tillage has had on wildlife conservation lands around St. Denis, Sask., where sloughs have dried up.
“We’ve become very efficient water managers in the last 30 years,” he said. “We change things and we change the hydrology of the Prairies.”
There are several snow trapping techniques available to farmers:
- Trap strips: Trap or deflector strips are narrow lines of tall stubble in the field. They are usually 40 to 60 centimetres wide and can be created by attaching a V-shaped deflector unit to the swather or combine header.
The deflector separates and bends the stems of the crop sideways, so they are cut to form a strip of stubble in the shape of an inverted V, about 250 mm higher than the nearby stubble.
- Alternate height stubble: This practice involves harvesting a crop and leaving bands of stubble of alternating heights within a field. Studies around Regina found that stubble crops can double the accumulation of snow.
Deflector strips cut off heads but leave a lot of stubble, which act as mini snow fences, trapping a lot in good snow years. The height of cut on the swather is changed on each round of the field. It produces a series of bands of stubble, each the width of the swather from 15-30 cm to 30-60 cm.
Research in a field at Eston, Sask., found the bands of tall stubble resulted in an estimated increase of 30 mm of snow water over fields with uniformly low stubble.
Alternate height stubble and trap strips are generally more effective in trapping snow than level tall stubble, but the benefits vary with snowfall and wind.
Typically up to 60 mm of additional water equivalent can be gained over a field in southern Saskatchewan by these stubble management techniques.
- Tall stubble: High stubble is often seen in straight combining, with the height varying 30 to 70 cm. It normally catches a significant amount of snow each winter.
Blowing snow in open areas can remove up to three-fourths of annual snowfall. Wheat stubble in southern Saskatchewan reduces snow loss by half compared to that on fallow fields.
- Snow ridges: Parallel ridges of earth and snow are plowed into the fields at regular intervals to trap more snow. They should be oriented perpendicular to the primary blowing snow direction, typically northwest to southeast on the Prairies.
The drawbacks to this technique include mid-winter melts and packing down of ridges, which reduce their size and collection capacity.
The ridges stick up so they are prone to evaporation when a dry warm wind hits them. Snow walls contaminated by dirt will also melt down faster.
The cost of fuel and wear and tear on the tractor are other deterrents to the use of snow ridges.
- Shelterbelts, windbreaks and fences: A host of plants, from carragana and ash to sudan grass and tall wheatgrass, can be used to trap blowing snow.
One tall barrier is usually more effective than several shorter barriers. Porous fences are more efficient than solid fences in trapping snow and maximum drift lengths can be 35 times the fence height.
Fences should be taller than the height of average winter drifts in order to trap snow effectively.
