Surface Urban Heat Islands changes analysis considering the effects of Covid-19 lockdown

In this research, the effects of Covid-19 lockdown and limitations on human activities were investigated on urban heat islands. The multi-temporal images which were taken by the Landsat-8 OLI sensor in the spring 2017-2021 were used. For investigating the effects of lockdown in the spring of 2020, the status of surface urban heat island (SUHI) maps during the same period of lockdown in the three years before and the following year have been examined. The proposed method in this paper consists of two main steps: (1) producing the SUHI maps using the rule-based analysis of land surface temperature (LST), normalized difference vegetation index (NDVI) and land use/land cover (LULC) maps and (2) quantitatively analyzing the behavioral changes in the SUHIs during Covid-19 lockdown and comparing their changes with the previous and subsequent years. The obtained results of performing the proposed post-classification change detection confirm that applying the lockdown led to changes in the area percentage of high, medium and low SUHI classes by -17.61%, + 4.8% and +12.8%, respectively. Reducing the restrictions in 2021 caused an increase again in the area of high SUHI class by +18.87% and a decrease in the areas of medium and low classes. Change analysis considering LULC object types reveals that the area percentage of high SUHI class in built up is decreased by -7.48% in 2020 compared to its average of three years before lockdown (which is 6.1% more than decreasing in vegetation cover). In addition, the analysis of LST and NDVI obtained from Landsat-8 satellite images in the years 2017 to 2021 reveals that the Covid-19 lockdown applied in spring 2020 caused a decrease of -22.52 in LST values and an increase of +0.103 in NDVI compared to the average of its last three years.