Abstract: The May-July period over the Canadian Prairies in 2010 was the wettest in 60 years and possibly 100 years. In July the federal and three prairie provincial governments announced $450 million in funding to assist waterlogged farmers. Causal factors are considered to be El Nino conditions during the past winter and spring months, below normal North American snow cover in April and extremely low sunspot activity.

The Canadian prairies produce over 50 million tonnes of grain, over half of which is wheat. In terms of planted area, yield and quality the most weather-sensitive months are May-September with May-July being the most critical for yield. (Garnett 2002). The prairies are one of the most drought-prone regions in Canada, where droughts (recurring or irregular) of moderate-to-severe intensity have occurred for hundreds of years (Khandekar, 2004). The recent drought years of 1999-2002 are fresh in the memories of many Prairie farmers. That drought period prompted several Alberta University professors to write to the then-Premier of Alberta, Mr. Ralph Klein, an ‘Open Letter’ urging him to support the Kyoto Accord and to develop a GHG (Greenhouse gas) reduction strategy for Alberta and by extension the other Prairie Provinces (The Open Letter was published in major newspapers in Alberta in July/August 2002). The Open Letter further suggested that droughts on the Prairies could be exacerbated as human-induced concentration of GHGs would continue to increase in the future.

Against this backdrop, it is worth noting that April to September of 2010 brought more than 150% of normal rainfall to the prairie grain-growing region. The months of May through July were the wettest in the last 60 years and possibly in 100 years. This summer’s almost record-breaking rains on the Prairies were reminiscent of the summer 2005, when parts of the city of Calgary as well as several other localities on the Prairies were flooded. For the prairies as a whole May-August 2010 brought 144% of normal precipitation compared to 122% of normal in 2005.

The 2005 flood situation on the Prairies prompted (the then) Prime Minister Rt. Hon. Paul Martin to make a special visit to the Prairies and declare emergency funding for flood affected regions. As this summer’s harvest season continues, prospects are for a significantly reduced harvest, primarily due to excessive rains and delayed sowing due to waterlogged farms into early June. Why are the Canadian Prairies subject to such extreme drought/wet summers?

What is driving the summer rainfall pattern? In this short article we analyse Prairie drought (and wet periods) using a simple teleconnective analysis of large-scale atmosphere ocean and snow cover patterns plus a new approach developed recently by Garnett et al (2006).

Concluding Remarks

This past summer’s excessive rains on the Canadian Prairies appear to be due to a favourable combination of SSTs in the equatorial Pacific in conjunction with solar impact related to diminished sunspot numbers. Besides SSTs and low sunspot activity, a lower-than-normal snow cover during the spring months (April-May) may also have helped in producing a near-record rainfall on the Prairies.

The current solar minimum has not been equalled since 1933 (Livingston and Penn, 2009). These authors (Livingston and Penn) further project sunspots to vanish altogether by 2015.

What is in store for the summer of 2011? The La Nina conditions have been strengthening in recent months with sea surface temperature anomalies at the Nino 3.4 region averaging -1.2C below normal for the past three months. This is almost two standard deviations below normal.

Persistence of La Nina conditions for next spring (2011) together with continuing low sunspot activity may determine summer precipitation on the Prairies for 2011 and possibly beyond.

Could the Solar Cycle 24 (2010-2021) now commencing, parallel conditions experienced by Manitoba’s Selkirk Settlers who arrived in the Red River region between 1795 and 1823 during the Dalton Minimum of the sunspot cycles? In those years, sunspot activity failed to reach 50 sunspots per month. The settlers experienced frost, floods and locusts and probably would not have survived had it not been for the estimated 60 million bison that roamed the
Great Plains around 1800 (Green, 1974). A recent book (Plimer 2009) describes the Dalton Minimum period as an extraordinarily cold time in Europe. How the Prairie summer weather evolves in response to the equatorial Pacific SST distribution and low sunspot activity over the next few years remains an important research area at present.

Read the full analysis here.