Microclimate Modification by Urban Shade Trees – An Integrated Approach to Aid Ecosystem Service Based Decision-making

Abstract

Since microclimate regulation is one of the most important services of vegetation that is directly perceived by urban population, many studies aimed to evaluate and map this service on different spatial scales. Most of the investigations focused on the modification of only one parameter, namely the reduction of air temperature. However, it is important to state that thermal sensation, health and well-being are influenced by more atmospheric parameters, including air humidity, wind velocity and the three-dimensional short- and long-wave radiation environment as well. This necessitates the assessment of the modification effect of urban vegetation on the thermal components separately. With the above mentioned objective, this paper presents the initial results of a microclimate investigation series carried out in Szeged, South-East Hungary. Systematic on-site measurements were carried out with a pair of special human-biometeorological stations on 20 clear summer days of 2015 in order to reveal the small-scale climate regulation potential of single trees in urban environment. Five healthy, mature trees were selected for the analysis, without the disturbing (additional shading) effect of any other trees or artificial objects. We compare separately the median values of the main thermal parameters – air temperature, relative humidity, as well as the short- and long-wave radiation components from the upper and lower hemisphere – measured under the canopy of the trees, and in the sun. Our results demonstrate that all of the five investigated tree specimens have significantly greater impact on the components of the radiation budget, while the modification of air temperature and humidity is rather small. Inter-species differences seem to be small in the warmest hours of the day, and may be attributed to the dimensional and canopy-characteristics. During the development of ecosystem service indicators it would be advisable to use integrated human-biometeorological indices which take into account all meteorological parameters that influence considerably human thermal comfort.