Satellite-Driven Assessment of Surface Urban Heat Islands in the City of Zagreb, Croatia

Abstract

Abstract. This study aims to assess surface urban heat islands (SUHIs) pattern over the city of Zagreb, Croatia, based on satellite (optical and thermal) remote sensing data. The spatio-temporal identification of SUHIs is analysed using the 12 sets of Landsat 8 imagery acquired during 2017 (in each month of the year). Vegetation cover within the city boundaries is extracted by using Principal Component Analysis (PCA) data fusion method on calculated three vegetation indices (VI): Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and Ratio Vegetation Index (RVI) for each set of bands. The first principal component was used to compute the land surface temperature (LST) and deductive Environmental Criticality Index (ECI). As expected, the relationship between LST and all VI scores shows a negative correlation and is most negative with RVI. The environmentally critical areas and the patterns of seasonal variations of the SUHIs in the city of Zagreb were identified based on the LST, ECI and vegetation cover. The city centre, an industrial area in the eastern part and an area with shopping centers and commercial buildings in the western part of the city were identified as the most critical areas.

The Urban Heat Island Analysis for the City of Zagreb in the Period 2013–2022 Utilizing Landsat 8 Satellite Imagery

“…Specific hotspots, the hottest points in the City of Zagreb, coincide with extensive facilities such as shopping centres and industrial zones that consume and emit a lot of energy and residential areas. The same conclusion was presented in a year-long study of Zagreb's UHI, confirming the results' reliability [18]. Industrial zones in the western and eastern parts of the city are continuously represented as UHI hotspots on the maps.…”

“…For the City of Zagreb, the study area in this research, data on the relationship between LST (SUHI), and several vegetation indices have already been presented for 2017. The results showed a significant contribution of vegetation to urban climate regulation in a local context [18]. Furthermore, the results of this study also confirm the suitability of the remote sensing methodology in calculating LST for the City of Zagreb, with high correlation values found between in situ measurements and calculated LST during the day time [18].…”

“…The results showed a significant contribution of vegetation to urban climate regulation in a local context [18]. Furthermore, the results of this study also confirm the suitability of the remote sensing methodology in calculating LST for the City of Zagreb, with high correlation values found between in situ measurements and calculated LST during the day time [18]. In the study area, more research has been conducted in climatology and meteorology using more in situ measurements to describe and explain long-term climate change in the City of Zagreb [41][42][43].…”

“…Intensification of the published research exploring UHI within city boundaries can be noticed since 2014 at different spatial scales from meso-to micro-scale [8]. The diverse LST values within urban landscapes are expressed as the SUHI or the surface urban heat island and have far-reaching consequences for the city and its residents [6,15,18].…”

“…TIRS sensor can note neighbouring parts of the spectrum ranging from 10 to 12 µm, which allows the precise calculation of the LST using the data about atmospheric throughput and reflection collected by the satellite. Based on the aforementioned, Landsat 8 allows the simple calculation of the LST, and, consequently, the UHI, environmental critical index (ECI), and other indicators related to the LST from the same satellite imagery [18]. Thermal remote sensing represents one of the essential tools and methods employed that results in high-precision measurements of thermal properties inside cities with a resolution ranging from 30 m to 1 km, depending on a chosen satellite [8].…”