Assessing Urban Heat Island Effect and its Correlation with Topography and Surface Vegetation Characteristics in Mashhad City (NE Iran): Case Study on a Local Climate Change

Development of cities and reduction of green spaces is one of the important and influential factors in the formation of heat islands, a phenomenon that has become one of the important problems in cities. The urban heat island (UHI) is a concept that refers to the increase in temperature in urban areas compared to rural areas or urban outskirts. This temperature increase is due to the abundance of buildings, roads, parking lots, and other human structures in cities, as well as the reduction of green spaces and water, and also the increase in human activities such as traffic and industries. This study conducts an analysis on the complex relationships between topography, surface biophysical properties, and the UHI effect in Mashhad city (NE Iran), serving as a local case study for understanding climate change impacts. For this purpose, land use was extracted from Sentinel 2A images using the object-oriented processing method of satellite images. In the next step, using the thermal bands of Landsat 9 images and the MODIS sensor, urban heat islands were calculated for the city of Mashhad during the day and night. Finally, the correlation between temperature distribution during the day and night with land use, topography, vegetation, etc. was calculated. According to the obtained results, the significant loss of vegetation within and around the city has contributed to notable changes in surface characteristics. The transition from a relatively cool temperature layer (25-29 °C) to an average temperature class (33-37 °C) indicates the impact of vegetation loss on local dynamics. Moreover, the manipulation of slopes around the city has led to temperature increase, resulting in the emergence of hot (41-44 °C) and very hot (45-47 °C) temperature classes. The redistribution of surface clusters, particularly in the northwest, south, and southwest of Mashhad, is linked to specific land use changes. Additionally, the temporal variability of surface temperatures was examined, revealing the highest temperatures in July and August and the lowest in Azar. The spatial range of surface temperature exhibited seasonal variations, with the highest range observed in April and spring and the lowest in October and autumn. Moreover, the observed changes in surface temperature patterns highlight the significant impact of anthropogenic land use modifications on local climate dynamics. The expansion of the urban heat island phenomenon in Mashhad is evident through the overall increase in surface temperature and the reduction in temperature differentials between urban areas and their surroundings. Overall, this research provides important insights into the complex interplay between topography, land use changes, and surface dynamics in Mashhad, emphasizing the critical role of land use changes in shaping local climate patterns. It underscores the need to consider environmental impacts, urban development decisions, and land use planning to address the challenges posed by the expanding UHI effect and promote sustainable and climate-conscious development.

Keywords: Urban Heat Island, Surface temperature, Land use changes, Topography, Mashhad, Environmental management, Urban planning, Spatial analysis.