More humid than usual? It might be the corn

This is a cornfield in Mill Hill, Pa., on Aug. 29, 2023. (AP Photo/Gene J. Puskar)

As the summer heat settles in, many Canadians will feel the above-average temperatures and thick humidity, Environment Canada forecasted in June.

While sources of humidity often come from places such as the Gulf of Mexico, the real culprit may be close to home — our own crops and vegetation.

According to Environment and Climate Change Canada senior climatologist David Phillips, "evapotranspiration" or "crop sweat" is a major contributor to rising humidity levels and could fuel more extreme weather.

What is evapotranspiration

Evapotranspiration is the process by which plants absorb water through their roots, use it to hydrate and cool themselves, and then release that moisture into the atmosphere through tiny pores on leaves known as "stomata."

Phillips says this is similar to how humans sweat to regulate their body temperature. "All crops sweat, all crops evaporate."

"If there is a good amount of moisture, almost [like] an engine goes on. Through photosynthesis the plants are creating protein and the crops of corn or berries are growing," Phillips says.

Phillips adds that the volume of moisture released can significantly impact the surrounding environment.

Rising humidity levels

Phillips says a single hectare of agricultural land can evaporate up to 40,000 litres of water into the air every day.

"We're talking a huge amount of moisture," he says.

The closer the air temperature and dew point — or the temperature at which air becomes saturated — are, the more humid it is, he added.

Corn belts

This influx of moisture comes from more than just the Canadian Prairies. The U.S. Corn Belt, which spans several states including Illinois and Iowa, boasts around 90 million acres of corn, according to Phillips. Meanwhile, Canada has four million acres of corn in provinces such as Manitoba, Alberta, Saskatchewan, Ontario and Quebec, he says.

"So a lot of the heat that we feel from crop sweat will come from the United States," Phillips says.

Phillips says soybeans, potatoes and wheat also grow around this time and can add to the humidity.

Wilder storms

Crops moisture doesn't just make the air feel stickier — it can also fuel more extreme weather events.

Phillips explains that the additional humidity can act as "fuel" for thunderstorms, causing them to become "supersized" and more destructive.

Phillips says this could include hail, strong winds and other weather.

Phillips says, "Crops do create weather, and often it just augments or adds to whatever the current situation is. So it can make it worse. It can energize that storm. It can push up into the atmosphere."

"This creates a situation where the moisture condenses, it releases energy, or energy storm, and the storm gets wilder," he adds.

So the next time you're sweltering in the summer heat and humidity, remember that not just bodies of water contribute to the soupy air. Your local crops, from corn to soybeans, are likely pumping moisture into the air too.