History Shows This Season Will Be Dry. Or Wet. Maybe

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“It is quite striking though, that we’ve had a lot more very dry years in the last 10 years than in the past.”

AF contributor

lethbridge

Some people note the date of a fog on the calendar and confidently predict rain 90 days later. Others prefer to put their faith in the Old Farmer’s Almanac or the predictions in their favourite farm publication.

“I hope the fog-theory believers are right,” says Ralph Wright, soil-moisture specialist in the Alberta Agriculture agrometeorology applications and modelling section. “Moisture across the province is at a one-in-25-year low. That means many areas will be in real trouble if they don’t get at least normal precipitation in spring and during the growing season.”

Wright says there’s no scientific way to predict whether this will be another dry year. “It appears to be totally random. Wet years follow dry and dry years follow dry. There’s no apparent pattern to help us predict the sort of growing season we’ll have. It is quite striking though, that we’ve had a lot more very dry years in the last 10 years than in the past.”

The first thing is to understand what is normal for each part of the province, says Wright. Then, the important thing is how different the current situation is from normal. This year, soil moisture is very low in many areas, but normal or above-normal moisture in the next few months could make a big difference.

The main months for moisture are earliest in areas south of Calgary, with six to eight per cent of annual moisture arriving in each of March and April, then 14 to 18 per cent in May and again in June. As spring spreads north, areas from Red Deer north get to eight to 12 per cent of their annual moisture in May with areas north of Edmonton seeing high-moisture months even later.

Areas north of Calgary get as much as 20 per cent of their annual precipitation in June and again in July. In the Peace country, peak moisture is even later with significant August rains, but snow accumulation contributes more to soil moisture than it does in other areas.

Records online

Wright uses records from the province’s 273 stations to model soil moisture. The old system of having a person probe fields and hand-test soil moisture is now used only to “ground-truth” the models. The old system is less precise, but checking at 300 points across the province each year shows the models are accurate.

Wright has been using the weather records to develop maps of temperature and precipitation over time, going back to 1961. There are thousands of these maps in the AgroClimatic Information Service (ACIS) pages of Alberta Agriculture’s website. “The maps give really good perspectives on weather relative to normal in all areas,” Wright says. “A person might see, for example, that some areas are likely to be short of hay, or have particularly good crops, so they can hedge their bets. We can’t predict weather beyond the next week or so, but good information on the current situation can help a lot.”

Wright says that the data allows the province to see long-term weather changes and recognize any climate-change effects.

“If areas are in long-term drought we can calculate water storage needs. We can quickly see shifts in weather patterns and tie them to crops, perhaps we can expand high-value crops or calculate the risk for a crop in an area.”

More sites coming

To expand the use of Alberta Agriculture’s high-quality weather data, it is posted immediately to the web where the public and researchers can access it. “We hope to add another 50 weather stations to the system with help from the federal government, and Alberta Sustainable Resource Development is planning to add their 180 weather stations to the ACIS website, providing even more accurate information,” says Wright.

Various organizations subscribe to the instant information. Specialcrops groups use it to forecast disease outbreaks, custom sprayers or farmers with widespread operations can check conditions in other areas. AFSC uses the information provide crop insurance programs and to gauge the extent and severity of storms or frosts.

Anyone can access hourly or daily information from any or all of the weather stations. Power uses can get automatic data feeds by subscribing to the ACIS RSS feed. In addition, you can access thousands of maps of normal and current moisture and heat unit accumulation at Alberta Agriculture’s ACIS site. A Google search for Alberta Agriculture weather maps will also bring up the site. You may need to choose “maps” from the left side of the main page.

www.agric.gov.ab.ca/app116/quick.jsp

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