The air temperature in urban areas is often systematically higher compared to their more natural surroundings. This difference in temperature is known as the “urban heat island” effect. Urban heat islands vary considerably depending on the size of the city, the amount of greenery, and how densely built up and well ventilated it is.
The urban heat island effect is one characteristic of a city’s microclimate that can form in any season. The urban-rural temperature difference is especially visible during summer and at nighttime. In Swiss cities, the temperature at night can be up to 5-7°C higher than in the surrounding rural areas. During the day, the temperature difference between urban and rural site is usually smaller, and air temperatures in cities are often only slightly elevated.
Due to the climate change-induced rising temperatures the issue of urban heating becomes ever more pressing. People living in urban areas tend to be more exposed to heat stress and the resulting health risks compared to people living in non-urban areas.