An analytical framework for estimating the urban effect on climate

The surface energy budget has been used to illustrate the influence of urban landscape on both global and regional climate. This was done using empirical as well as remotely sensed data of components of the surface energy equation. At the global scale, the urban land cover has the least impact on the sensible and latent heat fluxes compared to the other land cover types. Replacing the urban land cover with vegetation did not result in a significant change to the proportionate values of the turbulent fluxes originally due to vegetation. The least impact of current urbanization on the global climate in terms of radiation and surface fluxes is because the urban land cover has the smallest fraction of all the land cover types. The relative importance of the urban landscape at the regional scale was illustrated using the example of Chester County and surroundings near Philadelphia, Pennsylvania, in the USA. The urban effect becomes more important as the fraction of urban land cover to the total increases. This is illustrated by computing turbulent fluxes for 1987, 1988, 1991, 1993 and 1996 over the Chester County area. Urbanization in Chester County and surrounding areas increased from 11% in 1987 to 19% in 1996. In 1996, urban land cover produced the largest proportionate sensible (21.4 Wm−2) and latent (14.2 Wm−2) heat fluxes during winter. During the 1996 summer, urban and vegetation land cover produced the largest proportionate sensible heat (59.2 Wm−2) while urban land cover produced the second largest proportionate latent heat flux (39.5 Wm−2). The implications of this simple analytical study point to the need to account for the urban landscape particularly in regional studies. Copyright © 2009 Royal Meteorological Society