Land use as key element for urban heat island inception in small cities. Case study: Barlad City, Romania

Abstract

The study investigates the thermal characteristics of the urban area of Bârlad city, Romania, in relation with urban land use (LU) and land cover (LC). This was done using Land Surface Temperature (LST) data provided by Moderate Resolution Imaging Spectroradiometer (MODIS) and mobile measurements conducted during stable atmospheric conditions. To identify important factors that influence Surface Urban Heat Island (SUHI) and Canopy Layer Urban Heat Island (CLUHI) two types of LU/LC classifications were used. At the annual level, during the day, the highest LST values are observed in the most densely built-up areas of the city, with values exceeding 18°C. The lowest LST instead are observed in the northern area of the city, with prevailing natural areas, where LST values reach 17.4°C. During the night, the urban area maintains constantly high LST above 4°C, while the lowest LST values are observed in the forested area in the eastern part of the city, where mean LST drops close to 3°C. The results of this study highlight the significant impact that LU/LC has on the inception of SUHI in small cities. Generally, built-up surfaces from Urban Atlas (UA) and Local Climate Zones (LCZ) classifications, are warmer than natural land cover types, both during day and night, with at least 0.5 to 1.5°C, which is enough to outline a clearly delimited SUHI especially during summer days. During stable atmospheric conditions the CLUHI exhibits large intensities emphasized by local cooling processes manifested especially during thermal inversion conditions.