The relationship between urban vegetation and land surface temperature in Isfahan city using Landsat TM and OLI satellite images and LST index

During the past decades, population growth, rapid industrialization, increased air pollution at low levels of the atmosphere, and the impact of heat island have caused dramatic changes in the local climate of the big cities. The release of heat energy increased greenhouse gas emissions, and land use change are among the main causes of local climate change in cities. The effects of urban environments on the atmosphere appear more often as thermal islands. Green space would be effective in reducing the temperature and increasing the humidity, and finally reducing the thermal island phenomenon as well as reducing runoff, improving the comfort of the citizens and, ultimately, the sustainability of the urban environment. The objectives of this study were to prepare land use maps and NDVI vegetation index, as well as land surface temperature maps, and to study the distribution of thermal patterns of land surface and temporal and spatial variations of vegetation and their relation in Isfahan from 1985 to 2016.

For this purpose, satellite imagery was downloaded from the US Geological Survey site. Using the three Landsat satellite TM images of August 1985, 2010, and 2016, the NDVI index was quantitated using Terrset software, and their maps were prepared. Then, by generating land use maps using the maximum likelihood supervised classification method, the analysis of the changes in land uses (such as city, road, agricultural fields, barren lands, river, mountains, and green spaces) was done. Finally, Land Surface Temperature (LST) index was used to estimate the land surface temperature (LST) and its relationship with the vegetation maps.

The trend of land use/cover changes in the study area showed that during the study period, severe degradation occurred in the green space of the area and the main part of these changes was the conversion of green spaces to urban areas. Also, the results indicated an inverse relationship between LST and NDVI index. The results showed that the growth of urban heat islands was toward areas that had encountered poor vegetation and developed constructional uses (residential, industrial, etc.). The results also indicate an accelerated increase in temperature in recent years compared to previous years, as the average annual temperature increase in the period from 2010 to 2016 was 0.61 °C, while the average temperature increase of 0.05 °C was observed from1985 to 2010.

The analysis of the changes in thermal islands of Isfahan was indicative of the increase of thermal islands and spatial reduction in urban cool areas. It can be concluded that the changes occurred in this 30-year period (1985-2016) in various aspects, such as population increase, urban area increase, and land use change eventually increased the area of hot spots. Because of the correlation between surface temperature and NDVI vegetation index, the necessity of protecting vegetation and green space, especially in urban areas, is a critical variable for climate change modification for responsible institutions in urban management. The results of this study could provide critical insights on precise and effective urban vegetation management with the purpose of Urban Heat Island mitigation for urban planners and managers.