It is estimated that by聽, 70% of people will live in cities.
This is a staggering statistic to bear in mind while you take a trip down memory lane. Remember summers in the city? The thick air wrapping itself tightly around your body? Or the oppressive stench of garbage baking in the summer heat? Or, my favorite, the constant beads of sweat dripping from places on your body you didn't even know were capable of sweating? Maybe that鈥檚 why so many people are eager to leave when school鈥檚 out.
As someone who spent my summers in New York City growing up, I mastered the art of beating the August heat. From dabbing cold water on my wrists, to spotting the trees with the best shade in the park (a secret I鈥檒l never reveal!). I learned how to survive New York heatwaves.
We owe the summertime stickiness in part to the urban heat island (UHI) effect. The UHI effect is a fancy way of describing the ways in which cities trap heat and feel warmer than the surrounding suburbs. In fact, average daytime temperatures in cities are聽聽than areas outside of the city, and nighttime temperatures are about聽.
Cities feel hotter because urbanization often replaces natural surfaces like vegetation, soil, and bodies of water with roads and buildings. This replacement is significant because these natural areas cool the air via a process called聽, while also providing shade.
Evapotranspiration is the combination of transpiration and evaporation. Transpiration happens when the roots of trees and vegetation absorb water and then emit it through their leaves. Evaporation takes place when water is converted from a liquid to a gas. These two processes work together to cool the air by using the heat in the air to evaporate water.
But it is not just the removal of water and greenery that contributes to a warmer city. The聽聽we use to build cities such as asphalt, concrete pavements, and tar roofing reflect fewer infrared wavelengths, absorbing them instead. With nowhere else to go, this heat is reemitted into the atmosphere, making us feel warmer.
However, not all urban heat islands are created equal.
聽published in 2023, researchers found that 64% of community districts in New York City showed high incidences of heat vulnerability. Most of these communities were in the boroughs of the Bronx or Brooklyn. This study found that social vulnerability in NYC was strongly associated with poverty prevalence. The authors concluded that, in NYC, poorer communities are more likely to live in neighborhoods that are more exposed to聽.
There鈥檚 more.
This study also found that within the communities studied in New York City, the more densely populated a neighborhood was, the less green space there was. Further, they identified that there is greater exposure to green space in more affluent communities, as opposed to those living in low-income neighborhoods. To live in a city does not have to mean to live without nature. For some, they are afforded the luxury of living amongst beautiful urban parks and green spaces. For others, this luxury is not a reality.
It鈥檚 hopeful to see that greening efforts like planting trees, implementing street gardens, or building parks have gained traction as viable solutions to this issue. But how do we make sure this development is equitable? Is there a way to give communities autonomy and therefore the necessary resources to cultivate their own green infrastructure?
Researcher Carson Silvera and his team think so.
聽led by Silvera, he and his team investigated the role and importance of private gardens to mitigate the UHI effect and microclimate regulation. A聽聽describes the climatic conditions of an area of land, usually less than a square kilometer. His study compared the power of green public spaces versus green private spaces to influence microclimates across Rio de Janeiro, Brazil.
It turns out that private green spaces, such as in people鈥檚 yards, are more helpful for cooling than parks and other public green areas. Why? Likely because there is more of it across the city, cites Silvera. An important finding was that it doesn鈥檛 always matter how much green space there is, but where it is located, and how it is arranged. This means that even a bunch of small patches with irregular edges of greenspace can have an impactful influence on microclimates, if they are designed well.
So this begs the question: Is your herb garden nature鈥檚 AC? The answer is unclear. Research on the cooling effects of private greenspaces is scarce, with Silvera鈥檚 being one of the few scientists studying the issue. While your modest herb garden may not make you feel cooler, it can offer other benefits. These small green spaces can foster a sense of connection with nature, which is especially valuable in urban areas. Your herb garden, though small, can provide a refreshing touch - or a breath of fresh air, no pun intended - in the concrete jungle.
So, while your basil and mint may not replace your AC unit, they could still contribute to a more fruitful and nature-connected way of urban living.
Eva Kellner is a fourth year B.A.Sc. student in the Interfaculty Program in Environment.
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