For the same reason that sweating on a hot day cools us down, evaporation helps keep air temperatures cool as well. Stormwater systems however allow much less water to seep into soil than in rural areas. In cities, most rain water is funneled from rooftops, lawns,and pavement via drainage systems. A heat island map has been created for Chicago and the most severe areas correspond with the areas that have the fewest trees. These are being more heavily targeted.

Why are Nelly and the City of Chicago so concerned about the heat? The
most tragic reason is that heat waves kill and the heat island effect can contribute to the severity of these heat waves. The Chicago heat wave of 1995 for example killed 739 people in one week. More recently, the Chicago Marathon was called off earlier this month for the first time in its 30 year history due to heat. It is a daunting thought that there are more deaths due to heat in recent years than hurricanes, earthquakes, and lightning combined. In addition, the heat island effect is causing increased electric use from air conditioning due to elevated temperatures.

Unlike the song suggests, the best remedies probably don’t include taking off all our clothes. The City of Chicago created a plan to address the heat island effect, which includes replacing dark-colored surfaces with light-colored reflective surfaces, planting trees, green roofs, rain barrels and increasing impervious surfaces. Over 500,000 trees have been planted, many by local non-profit agencies. Chicago benefits from over 3.5 million square feet of green roofs either constructed or in the works. Instead of getting hot and bothered by the heat island effect, Chicago is taking actions to remedy it.