Evaluation of Vegetation Effects on the Generation and Modification of Mesoscale Circulations

Abstract

The purpose of the present study is to evaluate (i) the effect of vegetated surfaces on modifying sea breeze and daytime thermally induced upslope flows, and (ii) the generation of thermally induced flow by vegetated areas contrasted by bare soil area. In order to address these objectives, the following tasks were carried out: 1) previous documented studies with implication for (i) and (ii) are reviewed; 2) the main features of the thermal balance of vegetated surfaces are outlined qualitatively; 3) a quantitative evaluation of the various components in the thermal balance based on documented observational studies is provided; and 4) scale analyses and numerical model simulations are used to provide quantitative evaluations of the circulations involved with (i) and (ii) for several illustrative cases. The study suggests that the impact of vegetated surfaces in those cases is highly dependent on the environmental conditions as well as vegetation characteristics. For ideal environmental conditions resulting in high evapotranspiration rates over extended dense vegetated areas, it is shown that the circulation types listed in (i) are substantially reduced. For the situation described by (ii), circulations with an intensity close to that of a sea breeze can develop when the vegetation is very dense, and covers an extended area, and under favorable environmental conditions. The reduction in these impacts for more frequent real world situations involved with less favorable environmental conditions as well as with relatively sparse vegetated areas is also evaluated.