SIMULATIONS OF ANNUAL DEGREE-DAY IMPACTS OF URBAN VEGETATIVE AUGMENTATION

One approach for reducing summertime energy consumption in cities is t hrough implementation of urban vegetation planting programs. While the direct effect of such programs is to cool individual buildings and ai r conditioning condenser units, there is also an indirect regional coo ling associated with increasing vegetative cover. This paper models th e regional cooling impacts of urban vegetation augmentation through a series of meteorological simulations. Numerical experiments were condu cted for a hypothetical city located at various latitudes (25-45 degre es N) and subjected to several background climate conditions. Simulati ons were conducted for one day from each month of the year to determin e seasonal variability of the impacts of vegetation on urban climates. To provide a simple and useful index of the climatic impact of urban vegetation, cooling and heating degree days were calculated for each s imulation. Comparison of baseline degree days for six modeled cities a t various latitudes across the United States with the corresponding hi storical climate data indicate that the modeling approach was successf ul in reproducing the general temperature profile characteristics of e ach city. Simulation results indicate that the regional climate can be significantly cooled through the planting of urban vegetation. For re gions of low-to-moderate ambient humidity, increasing the vegetative f raction of the core of a hypothetical city by less than 0.065 resulted in an estimated 3-5% decrease in summertime cooling loads. It is beli eved that this effect could be doubled by application of a more ambiti ous program. This energy saving is due to the indirect regional coolin g effects of vegetation, and does ndt include the direct energy saving s associated with shading of individual buildings. The wintertime ener gy costs associated with vegetative augmentation were found to be smal ler than the summertime savings, and may be negligible in the case of deciduous vegetation. (C) 1997 Elsevier Science Ltd.