Localized cooling thanks to paving that releases water vapor
In greater urban areas, the temperature can be as much as ten Kelvin higher than in surrounding rural areas, which has given rise to the term "urban heat island". To reduce this effect, the basic idea is for concrete paving stones to be able to store water. During the hot summer months, the water is transported as needed to the surface, where it evaporates and cools the stone surface in a process known as evaporation enthalpy. One effect of this integrated water store is to inhibit the concrete from absorbing and storing heat in the first place – it’s this absorbed heat that tends to prevent the concrete from cooling properly in the evening and at night. Initial measurements indicated that under certain conditions, a temperature drop in the region of ten Kelvin is realistic. This is a difference comparable to a dry concrete surface and a stretch of grass in the midday sun.