For a significant number of urban hydrological issues, for example, water supply, water quality, groundwater recharge, saline intrusions, and flood runoff, knowledge of evaporation rates is required. However, because little is known about the magnitude of these rates and their spatial variability, broad assumptions have to be made.
In this paper we investigate urban evaporation rates using both field observations and numerical modelling. First, directly measured summertime evaporation rates, using micrometeorological techniques (eddy correlation), in areas of seven North American cities (Chicago, Los Angeles, Mexico City, Miami, Sacramento, Tucson, and Vancouver) are presented. These data demonstrate the importance of urban evaporation and illustrate clear differences for downtown, light industrial and residential areas. Second, numerical modelling for one large North American city (Indianapolis, Indiana) is used to demonstrate the spatial variability of evaporation rates and the implications of land use change.