Weatherz School: Urban heat island effect

With big temp swings, fog, and lake effect snow, Lake Superior’s influence on our weather is common knowledge. However, our weather isn’t only influenced by natural features like the Great Lakes. Cities can be warmer than surrounding rural areas because of the urban heat island effect.

Vegetation is a key player in regulating temperature. An area of wildland with trees and grass can have a consistent high temperature. In this case, it’s 85 degrees. Once we develop that land and replace vegetation with a city, there are several factors that influence temperature.

Heat is emitted from cars, buildings and factories. Asphalt and dark rooftops retain heat much better than vegetation. Concrete surfaces reduce surface moisture. And, less trees means less shade and less cooling from evapotranspiration.

All of this together can lead to a temperature difference between 5 and 10 degrees. On a day that would have a high of 85 over natural landscape, it can be 92 downtown in a big city. This is the urban heat island effect. This effect is the greatest on days with sunshine and light winds. The Twin Ports isn’t a large urban area, but we can still experience a heat island effect.

As a country, the concrete jungle has come to replace a lot of green space. According to the 2010 U.S. Census, 80.7% of the population lives in urban areas. This is a 12.1% increase from the urban population in 2000 of 79%. What that trend was over the most recent decade has yet to be seen. The Census Bureau plans to announce final urban areas based on the 2020 census this December.

As urban population densities increase and natural land decreases, heat islands strengthen. This can exacerbate heat waves.