A reduction of evapotranspiration in urban areas results in higher surface temperatures. In the natural landscape most precipitation is evaporated or transpired whereas in urban areas, evapotranspiration is greatly decreased and rainwater is instead quickly directed to drainage networks. The increase of urban areas promotes a higher priority to decentralized measures of rainwater retention and new strategies in water supply and management. Rainwater is stored and used for irrigation, greening and adiabatic cooling.
The potential of achieving an evaporative cooling in Berlin is high since we are talking of a considerable annual storage (annual average precipitation in Berlin is of in of 500 mm).
With infiltrating decentralized systems, such as swales and swale- trench systems, a partial evaporation of precipitation is achieved. However, the proportion is only of about 10%.
The more effective measures lies within the following:
Tree-Drainage trench system, and raingardens