Abstract
In recent decades, unsustainable urban development stemming from uncontrolled changes in land cover and the accumulation of population and activities have given rise to adverse environmental consequences, such as the formation of urban heat islands (UHIs) and changes in urban microclimates. The formation and intensity of UHIs can be influenced not only by the type of land cover, but also by other factors, such as the spatial patterns of thermal clusters (e.g., dimensions, contiguity, and integration). By emphasising the differences between semi-arid and cold-and-humid climates in terms of the thermal-spatial behaviours of various types of land cover in these climates, this paper aims to assess the behavioural patterns of thermal clusters in Tehran, Iran. To this end, the relationship between the land surface temperature (LST) and the types of land cover is first demonstrated using combined multispectral satellite images taken by Operational Land Imager (OLI), Thermal Infrared Sensor (TIRS) of the Landsat8 and MODIS, and Sentinel satellites to determine LST and land cover. The effects of different behavioural patterns of thermal clusters on the formation of daytime urban heat islands are then analysed through spatial cross-correlation analysis. Lastly, the thermal behaviours of each cluster are separately examined to reveal how their spatial patterns, such as contiguity, affect the intensity and formation of UHI, with the assumption that each point in a contiguous surface may exhibit different thermal behaviours, depending on its distance from the edge or centre. The results of this study show that the daytime UHIs do not occur in the central parts of Tehran, and instead they are created in the surrounding layer, which mostly consists of barren cover. This finding contrasts with previous research conducted regarding cities located in cold-and-humid climates. Our research also finds that the more compact the hot and cool clusters are, the more contiguous they become, which leads to an increase in UHIs. The results suggest that for every 100 pix/km2 increase, the cluster temperature increases by approximately 0.7–1 °C. Additionally, placing cool clusters near or in combination with hot clusters interrupts the effect of the hot clusters, leading to a significant temperature reduction. The paper concludes with recommendations for potential sustainable and context-based solutions to UHI problems in semi-arid climates that relate to the determination of the optimal contiguity distance and land use integration patterns for thermal clusters.
Highlights
Changes in land cover have profound impacts on the formation and size of urban heat islands (UHIs) [1], i.e., areas that are measurably warmer than their surroundings [2,3].This is because many man-made land covers store solar energy and release it into the urban canopy at different times of the day
(3) In addition to assessing the effects of different land covers on the formation of UHIs, we investigate the influences of different spatial patterns of thermal clusters on reducing or increasing the effects of UHI in the context of a city located in a semiarid climate
We present the results obtained by following the procedures described in the methodology section to identify the impacts of the form and size of different types of land covers on the intensity of UHIs
Summary
Changes in land cover have profound impacts on the formation and size of urban heat islands (UHIs) [1], i.e., areas that are measurably warmer than their surroundings [2,3]. This is because many man-made land covers store solar energy and release it into the urban canopy at different times of the day. Within the context of urban climates, these microclimates primarily refer to UHIs. Having a higher temperature in the central parts of a city than in the peripheral areas raises the thermal discomfort of citizens, with negative consequences such as increased energy demands [11], air pollution [12], and mortality [13]
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