Climate Change in Southern Ontario

We would like to first make a distinction between weather and climate. These two often get confused with each other and it makes for confusing conversation. Climate is the prevailing weather in a region averaged over many years to describe the general humidity, temperature, precipitation and winds. Weather is the current, daily state of the atmosphere in a given location regarding heat, dryness, sunshine, wind and rain. Southern Ontario is experiencing a change in climate and it is affecting everyone, including farmers.

The consequences of climate change are accountable for the current trends and future projections of exposures affecting Southern Ontario crop production. Exposure is the result of being subjected to some effect or influence from a process of global change (Leichenko & O’Brien, 2008). Exposures can be further divided into primary exposures and secondary exposures. Primary exposures are systemic changes in temperature and precipitation that are irreversible. Some examples of primary exposures affecting Southern Ontario crops are increasing temperatures and a fluctuation in precipitation cycles. Secondary exposures are ecosystem level changes which occur in response to primary exposures resulting in a change in species composition, loss of land and increase in floods and droughts (Calvert, 2017). 

The average annual temperature in Ontario has risen by 1.4°C over the last 60 years. It is expected that this primary exposure will continue to worsen. This may not sound like very much, but it has a large impact. Models suggest that by 2050 the average annual temperature could increase by an additional 2.5°C to 3.7°C in Ontario (OCCIAR, n.d.). Secondary exposure events associated with increasing temperature include an increase in drought conditions, plant pathogens, and pest outbreaks. Ontario is expected to incur a greater frequency of heat events and droughts (OCCIAR, n.d.).

Droughts can severely affect crop production as large crops that do not receive sufficient rainfall require extensive irrigation measures in order to survive. Temperature has a large impact on the development of plant disease epidemics in Ontario. Disease will be prevalent if temperatures are more stressful for the plant than for the pathogen (Boland et al. 2004). With warmer summers and increased evaporation expected to occur, it is likely that drier periods will be more intense, creating less water available from runoff and low soil moisture (OCCIAR, n.d.). The increase in drought events and drought duration are very similar to the conditions previously experienced in the U.S. Midwest which lead to a 37% decrease in overall crop yield in a single year (Rosenzweig, 2001).

Pests thrive under conditions of higher temperatures as a result of their cold-blooded nature. The higher temperatures increase insects rates of development and can even shorten the time between generations, leading to an increased amount of pests overall (Rosenzweig, 2001). Larger pest populations are problematic, as they are able to disseminate further and faster, resulting in more damaged crop fields. As Southern Ontario is projected to have increased temperatures year round, this also increases the chance of pest survival, from year to year (Horst, 2017). Moreover, with crop stress becoming more prevalent, their susceptibility to pest impact and proliferation is only worsened.

Another primary exposure affecting Southern Ontario crop production is fluctuations in precipitation. Precipitation in Southwestern Ontario has experienced a dramatic change over the last 80 years (Tan & Reynolds, 2003). Annual precipitation had a significant decrease during 1978-1998 and then a weak increase during 1999-2013 (Government of Ontario, 2016). Future climates show more precipitation in winter, spring and fall and less precipitation in the summer. The monthly projected precipitation patterns are expected to remain the same in 2100, indicating that summers will continue to remain dry (Government of Ontario, 2016).

Extreme rainfall events are expected to become more intense and occur more often in Southern Ontario (OCCIAR, n.d.). Between 1979 and 2004 the southwestern part of Ontario received the greatest amount of heavy rainfall events in its recorded history (Chiotti & Lavender, 2008). The projected increases in both frequency and intensity of extreme rainfall events are expected to result in an increased summer flood risk (Chiotti & Lavender, 2008). Entire crop fields can be destroyed due to summer floods when the plants are still sensitive.

Now, low precipitation and increased extreme rainfall events may sound contradictory but this is a very dangerous combination. Low precipitation means we will experience drought and our daily atmosphere will be very dry. Extreme rainfall refers to storms that result in flooding.

The ground can only absorb so much before it reaches a saturation point. After this occurs the water sits on top of the soil and builds up, destroying everything in its path. Floods are especially worsened when the ground is dry and cracked due to low precipitation and its ability to absorb is weakened.

This is why adaption strategies in agriculture are so important. Read our other blog posts for more information on how farmers are coping with climate change!


Leichenco, R.M and O’Brien, K.L. (2008) Environmental Change and Globalization. Oxford university press. New York.

Ontario Centre for Climate Impacts and Adaptation Resources (OCCIAR), (n.d.). Agriculture: In a changing climate. Sudbury, ON: MIRARCO/Laurentian University.

Boland G. J., Melzer M. S. Hopkin A., Higgins V., Nassuth A. (2004). Climate change and plant diseases in Ontario. Can. J. Plant Pathol. 26, 335-350.

Rosenzweig, C., Iglesias, A., Yang, X. B., Epstein, P. R., & Chivian, E. (2001). Climate change and extreme weather events; implications for food production, plant diseases, and pests. Global change & human health, 2(2), 90-104.

Tan C.S., Zhang T. Q., Drury C. F., Reynolds W. D., Oloya T., Gaynor J. D. (2007). Water quality and crop production improvement using a wetland-reservoir and drainage/subsurface irrigation system. Canadian Water Resources Journal, 32(2), 129-136.

Chiotti, Q. and Lanender, B. (2008): Ontario, in From Impacts to Adaptation: Canada in a Changing Climate 2007, edited by D.S. Lemmen, F.J. Warren, J. Lacroix and E. Bush; Government of Canada, Ottawa, ON, p. 227-274.

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