Abstract
Surface urban heat island (SUHI) is defined as the elevated land surface temperature (LST) in urban area in comparison with non-urban areas, and it can influence the energy consumption, comfort and health of urban residents. In this study, the existence of daytime SUHI, in Cairo and its new towns during the summer, is investigated using three different approaches; (1) utilization of pre-urbanization observations as LST references; (2) utilization of rural observations as LST references (urban–rural difference); and (3) utilization of the SIUHI (Surface Intra Urban Heat Island) approach. A time series of Landsat TM & ETM+ data (46 images) from 1984 to 2015 was employed in this study for daytime LST calculation during summer. Different statistical hypothesis tests were utilized for the evaluation of LST and SUHI in the case studies. The results demonstrated that there is no significant LST difference between the urban areas studied, and their corresponding built-up areas. In addition, daytime LST in new towns during the summer is 2 K warmer than in Cairo. Utilization of a pre-urbanization observations approach, alongside an evaluation of the long-term trend, demonstrated that there is no daytime SUHI during the summer in the study areas, and construction activities in the study areas do not result in cooling or warming effects. Utilization of the rural observations approach showed that LST is lower in Cairo than its surrounding areas. This demonstrates why the selection of suitable rural references in SUHI studies is an important and complicated task, and how this approach may lead to misinterpretation in desert city areas with significant landscape and surface difference with their most surrounding areas (e.g., Cairo). Results showed that, although SIUHI technique can be representative for the changes of variance of LST in urban areas, it is not able to identify the changes of mean LST in urban areas.
Highlights
Urban Heat Island (UHI) is defined as significantly warmer air temperature in an urban area compared to its surrounding non-urban area, as a result of urbanization
SIUHI technique is only able to highlight the temporal changes in standard deviation (SD) of land surface temperature (LST) and this technique is not able to detect the temporal changes of mean LST in an urban area, which is due to urbanization
The other rural areas in the northern and southern parts of Cairo can be employed for evaluation of urban–rural difference, it is clear that the selection of suitable rural references in Surface urban heat island (SUHI) studies is an important and complicated task, and this approach can lead to misinterpretation as the urban–rural difference approach is highly dependent on the characteristics of the selected rural areas, especially in urban areas in desert
Summary
Urban Heat Island (UHI) is defined as significantly warmer air temperature in an urban area compared to its surrounding non-urban area, as a result of urbanization. Heat stored by surfaces and features in urban areas during the daytime is released at nighttime, and it has a lot of influence on the development of atmospheric heat island at nighttime. In 1950, around 29% of the global population lived in urban areas This proportion had grown to 47% by the year 2000, and it is predicted that this will grow to 69% by the year 2050 [2]. Urban areas are continuously growing [3], and the number of people exposed to temperature and heat stress impact is expected to increase [4]. The combined effects of growing urbanization and demographic change (e.g., population aging) increase both the risk of heat stress, and its mortality rates [5,6,7,8]. Strzepek and Smith [11]
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