Determination of the spatio-temporal character of the urban heat island effect in Ordu city center and its surroundings

This study aims to investigate the spatial and temporal character of the Urban Heat Island (UHI) effect in the case of Ordu city center and its surroundings. The UHI effect is a phenomenon characterised by higher surface and air temperatures in urban areas compared to the surrounding rural areas. Land cover change due to urbanisation and construction processes leads to the expansion of the areas under the UHI effect. Moreover, global climate change, which has accelerated since the industrial revolution, causes the impact of UHI to be felt more obviously in cities. The study includes Ordu city center and the rural areas in its surroundings. Remote sensing data and geographical information systems were utilised in the study. In order to reveal the temporal change of the UHI effect, thermal infrared data obtained from Landsat 7 ETM+ for the year 2000 and Landsat 8 OLI/TIRS satellites for the years 2013 and 2023 were converted into Land Surface Temperature (LST) maps. Then, the spatial distribution of the areas under the influence of UHI was revealed based on LST. The variation of the UHI effect between different Local Climate Zones (LCZ) was analysed. Based on the correlation between vegetation and built environment indices and LST, the contribution of surface characteristics to the UHI effect was evaluated. The variation of UHI effect in the urban-rural gradient was evaluated by multiple ring buffer zone analysis. The variation of the UHI effect between day and night time periods was revealed by using Random Forest Regression on low spatial resolution MODIS data. Finally, the cooling effects of urban parks, which are considered as an effective tool in mitigating the UHI effect, were evaluated. The findings show that the built-up areas expanded by approximately 65% in the period between 2000 and 2023 and significant increases occurred in terms of LST in the new built-up areas. The average LST has increased continuously over the years. During the 23-year period, the mean LST increased by 2°C, from 24.9°C to 26.9°C. In 2000, the areas under the influence of UHI, which corresponded to 13.9% of the study area, expanded to 19.2% of the area. The difference in LST between the UHI and non-UHI areas has also gradually widened over the years. In 2000, the difference between the two regions was 3.6°C, while it increased to 4.3°C in 2013 and 4.6°C in 2023. In the research area, the major locations where Urban Hot Spot formation is observed are industrial areas, metal roofs, artificial material artificial turf fields, areas with low vegetation cover and residential areas. The highest average LST values were recorded in Local Climate Zone (LCZ-2, 32°C) and LCZ-3 (31.2°C), while the lowest average LST value of 23.7°C was recorded in LCZ-17, which represents water bodies. In the study area, there is a high negative correlation between LST values and vegetation indices, while there is a high positive correlation between LST and spectral indices focusing on the built environment. While the average LST values decrease from the urban core to the rural areas, the vegetation cover ratio gradually increases. The difference in mean LST between urban and rural areas has also increased over time. The maximum temperature difference between the average LST values was 2.7°C in 2000, 5.9°C in 2013 and 7.2°C in 2023. In the research area; the difference between day and night surface temperatures has decreased over the years. In 2000, the difference between day and night LST was 11.5°C, whereas it decreased to 10.6°C in 2013 and to 8.5°C in 2023. While the day and night LST values have tended to increase significantly in urban areas, relatively lower LST levels have been observed in rural areas. As a result, Ordu is a city where the impact of UHI is becoming increasingly noticeable due to urbanisation. The results of the study provide significant information for local administrations, landscape architects working in the region, urban planners and policy makers in Ordu city center and its surroundings. With this doctoral dissertation, a spatial and temporal frame of reference has been drawn for Ordu city center and its surrounding area in terms of reducing the impact of UHI and developing strategies for adaptation to climate change.