URBAN HEAT ISLAND INTENSITY OF ZAGREB IN SUMMER AND WINTER SEASON

Abstract

The urban heat island (UHI) marks an area of higher temperature in the city compared to the non-urban surroundings. It is mostly caused by thermal properties of urban materials that easily absorb heat, but there are many other factors contributing to it. The UHI intensity is defined as the difference in spatially averaged temperature between urban area and non-urban surroundings. In the annual course UHI intensity is most pronounced in the cold part of the year. UHI intensity analyses was carried out using the data of seven meteorological and climatological stations in the city of Zagreb and surrounding area. The period of analyses was 1995-2014, which is the longest time series available for all stations. UHI intensity in the city of Zagreb was determined using average, minimum and maximum daily temperatures for summer and winter season. Additionally, the analyses for July and January, the warmest and coldest months in annual course of temperature respectively, were carried out. The occurrence of UHI intensity was also analysed since it was expected that differences in temperature would be highest in winter and in January. Higher temperatures in the stations in the city compared to the non-urban surroundings, especially in the cold part of the year, confirms the existence of a UHI. The variations and its causes in UHI intensity between different parts of the city of Zagreb was researched in the paper. Also, the impact of UHI on the increase of temperature in Zagreb was determined, where the highest temperature increase is expected in the stations in the city center.