In the temperate zone during a clear sunny day the income of solar irradiance is about 1000 W m-2, which means that an area of 1ha gets up to 10 MW of solar energy. What happens with this energy depends on the availability of water and the type of land cover (2, 5). Most of the solar energy on dry surfaces is converted into sensible heat, which warms up the ground and the air above it (3). In summer, temperatures of such surfaces can exceed 50°C. However, if the surface is covered by functional vegetation (and well stocked with water) 70 – 80 % of the energy can be dissipated through water evapotranspiration (the sum of transpiration and evaporation), which means conversion into latent heat, responsible for landscape cooling (2, 6). As a consequence of the cooling effect of evapotranspiration, the vegetation cover well supplied with water is substantially cooler than adjacent dry surfaces. This can be conveniently documented by means of thermo-vision (4).
The aim of this poster is to demonstrate how trees may work as a perfect air-conditioning system driven by the solar energy and using water. We present several IR photographs of towns with adjacent tree stands in South Bohemia (Czech Republic), which clearly illustrate how vegetation cover in urban areas have a substantial effect on the local climate.