The Gleaner

Warmer and wetter is the weather trend for the Chateauguay Valley


The regular weather reports are based on statistics that have been recorded in paper format as prescribed by Environment Quebec when the Ormstown weather station began in 1965. To develop the “trendlines” and “projections” referred to in this article required the appropriate computer skills to achieve the desired results, which this weather observer and recorder does not possess. As neighbour and good friend, Hugh Maynard offered to provide such a service for the benefit of our readers while using the 56 years of accumulated statistics provided from the Ormstown weather station.

The accumulated record of weather data over the last 56 years shows a trend toward warmer average temperatures and increased precipitation, and particularly so since the year 2000.

The rise in annual average temperatures is correlated by a similar rise in crop heat units, which is a measurement of cumulative heat during the growing season that farmers use to keep an eye on the progress of, particularly, their corn crop. Corn yields have also risen over the same time period, but there are other factors to take into consideration for this statistic, which we will look at further down in the article.


The annual average temperature for the last 56 years is 6.74 degrees Celsius, which is just over half a degree higher than the average temperature during the first decade of this period (1967-1976). However, over the last 23 years, since the year 2000, the average temperature has increased to 7.25 C, and five of the six warmest years (average temperature 8.0 C or higher) have occurred in this latter time period as well.


The warmest year was 2012, with an average temperature of 8.35 C, followed by 2020 at 8.31 C. The coolest year was 1972 (which was also the second-highest year for precipitation), with an average temperature of 5.35 C, followed by 1992 at 5.36 C.


Average annual precipitation – the sum of all the rain, freezing rain and melted snow over the last 56 years – now stands at 996 millimetres. This is only slightly above the average for the first decade (977 mm, 1967-1976) and only slightly below the average for 2000-2022 at 1052 mm. But the amount of annual precipitation has been steadily increasing, with three of the four years with precipitation in excess of 1200 mm occurring since 2000. The highest annual precipitation recorded over the last 56 years was this past year, 2022, at 1238 mm, and the lowest amount was 766 mm, and that was in 1988.

Crop Heat Units

Crop heat units (CHU) have also been steadily increasing over the last 49 years (the recording of heat units on the farm started in 1973). The annual average heat unit count is now 3104 CHU, which is 205 CHU more than the first decade of this period (1973-1982). However, over the last 23 years, since the year 2000, the average heat unit count has risen to 3259 CHU, and 10 of the 12 highest years for heat units have occurred since the year 2000. The highest CHU count was 3655 in 2021 and the lowest was 2684 in 2000.


Crop heat units (CHU) are calculated daily, using a formula that takes into account the maximum and minimum temperatures in order to account for a crop’s negative response to higher temperatures. The units are calculated (for this data set) from the day the first corn is planted (usually in the first half of May) until the date of the first killing frost (usually in the second week of October).

Keep in mind that the heat unit rating for the Valley in 1965, when grain corn production began in earnest, was considered to be 2650 CHU by provincial sources. We must also take into consideration other factors that have influenced total recorded heat units, not the least of which was tile drainage which was not common prior to 1980. This has added one to two weeks to the growing season and resulting heat unit accumulation. Also, GMO corn varieties have had cold tolerance and other positive factors bred into them which allows for the seeds to be planted into cooler soils and enables an earlier start to planting. In addition, climate change has extended the growing season in the fall but at the same time making it more difficult to determine the specific date of the killing frost (fewer hard frosts) compared to 40 years ago.

Corn Yield

So, it would make sense that if temperatures, crop heat units, and precipitation have all been on the rise, corn yields should increase as well. Well, they have, but there are other important factors that have influenced corn yield in recent years, so it is a challenge to correlate the increase in corn yields just to the weather.


The average corn yield on the Finlayson farm since 1978, when annual record keeping started, is 4.0 metric tonnes to the acre (mt/ac). Prior to this, in the late 1960s when corn production first started in the area, yields were around 2 imperial tons per acre, or 1.8 mt/ac. This compares to 3.3 mt/ac from 1978 to 1987, and 4.5 mt/ac since the year 2000. The highest-yielding year was 5.3 mt/ac in 2021 (also the same year as record CHU), and the lowest was 2.7 mt/ac, the first year records were kept on the farm in 1978.

Corn production is also influenced by several factors other than weather. The first is cultivation practices, which is probably not a substantive influence on the Finlayson farm given that these have not changed much since 1978 – the fields are plowed in the fall, harrowed and planted in the spring, and harvested in the fall. Many corn producers in the area have switched to no-till or minimum tillage where they seed the crop directly into the previous year’s plant residue without plowing. This can sometimes increase yields, depending on the weather and other agronomic practices.

The second influence is tile drainage, which was installed on the farm in 1977 and 1984. Tile drainage removes the excess water in the soil in springtime and during periods of heavy rainfall, allowing the land to dry out and warm up quicker, extending the crop season by up to several weeks. Tile drainage makes a recognized contribution to yield pretty much everywhere it is installed.

The third influence was the introduction of genetically modified corn seed, which was first planted on the Finlayson farm in the year 2000. GM seed has generally increased corn yields, anywhere from 5 to 20 per cent, depending on the variety, the soil type and other agronomic factors.

Where to next?

The trend for the region over the last 56 years has been warmer and wetter weather. A steady yet moderate increase for average temperature and precipitation over the whole period appears to be picking up pace in the second half of the time span. If the trend continues, then the average annual temperature will reach 8.0 C in 2038 based on the 56-year trend line, and as early as 2033 when extrapolating the 2000-2022 trend line.


The trend line for annual average precipitation is not quite as pronounced but still increasing, estimated to reach 1100 mm of precipitation by 2040 based on the 56-year period, and by 2035 based on the 2000-2022 period.

For crop heat units the trend line will also continue to rise, but at a slower pace. The estimate based on the 1974-2022 period reaches 3500 CHU by 2033, and by 2030 based on the 2000-2022 period.

For corn yields, there are too many variables beside the weather to make a prediction, but just for the fun of it, if the current trend line continues, average corn yields will reach 5.0 mt/ac by 2025 based on the 1978-2022 period, which is even quicker than the 2000-2022 period which gives an estimate of 2030 for the same yield. At that rate, maybe we’ll see 5.5 mt/ac by 2040?


Latest stories

UPA campaign highlights the work of farmers to bridge gaps

Callan Forrester

Syrup season ends after roller-coaster run

Sarah Rennie

Egg-handling upgrades increase productivity at Les Fermes Valens

Sarah Rennie - LJI Reporter

Leave a comment

* By using this form you agree with the storage and handling of your data by this website.

Follow by Email