Urban thermal effect in a high-altitude, semi-arid city: Tabriz, Iran

The urban heat island (UHI) is a ubiquitous outcome of urbanization, that is the transformation of the natural landscape and the concentration of human activities. These properties alter the natural surface-air exchanges, raising surface and air temperatures, which affects building energy use and thermal heat stress. However, the impacts of these changes depends greatly on the background climate. There have been significant advancements in UHI studies of cities in temperate climates located in high-income countries. Studies on high-altitude, cold, and dry cities are rare.  

This paper reports on a UHI study on the semi-arid city of Tabriz (Iran), which has a cold and dry climate (Köppen type BSk) and is situated at 1,350 m above sea-level. The city is almost confined entirely by mountain chains - with a significant elevation difference of around 200 m between its eastern and western parts - which resulted in a compact urban landscape. This built area is surrounded by bare lands that exhibit different diurnal thermal characteristics compared to cities located in temperate climates. An investigation into the nighttime canopy level UHI of Tabriz was conducted using a traverse approach during summer, revelaing the pattern and timing of the urban temperature effect.

This work builds on that research and focuses on the surface UHI over the course of the year. This study consists of several steps: (1) Characterizing city structure using Local Climate Zones along with socio-economic information; (2) Seasonal assessment of the diurnal urban thermal environment using remote sensing data, and; (3) linking it to the characteristics of the urban landscape using machine learning methods. 

The outcome of the study will reveal how UHI is beneficial to high-altitude cities in cold and dry climates and the implications of mitigating UHI in summer while enhancing it during cold seasons for energy efficiency.