Abstract
Urban heat island (UHI) is a phenomenon which may have adverse effects on our environment and is stimulated as a result of urbanization or land cover changes. Thermal remote sensing has been found beneficial to study the effect of urbanization on UHI intensity. This paper analyses the variation in land surface temperature (LST) with land cover changes in Varanasi city of India from 1989 to 2018 using Landsat satellite images. A new index named Urban Heat Intensity Ratio Index (UHIRI) was proposed to quantify the urban heat intensity from 1989 to 2018 which was found to increase from 0.36 in year 1989 to 0.87 in year 2018. Further, contribution of each land cover towards UHI was determined using land cover contribution index (LCCI). The negative value of LCCI for water and vegetation indicates its negative contribution towards UHI, whereas positive value of LCCI for bare soil and built-ups depicted its positive contribution towards UHI. The LCCI value for urban land cover shows significant increase in 29 years, i.e. 0.49, 1.43, 3.40 and 4.37 for years 1989, 1997, 2008 and 2018, respectively. The changes in normalized LST from years 1989 to 2018 for the conversion of bare land to built-ups and vegetation to built-ups were found to be as −0.11 and 0.42, respectively. This led to conclusion that the replacement of vegetation with urban land cover has severe impact on increasing UHI intensity.
Highlights
Urban heat island (UHI) is a phenomenon which may have adverse effects on our environment and is stimulated as a result of urbanisation or land cover changes
The Urban Heat Intensity Ratio Index (UHIRI) value includes both the contribution of temperature difference from built-up and natural land cover as well as proportion of built-up land in the study areas. This index has the potential to explain the effect of urbanisation on Land surface temperature (LST) in areas with greater heterogeneity in land-use and land-cover (LULC) types
In order to study the behaviour of LST with different LULC types, LST statistics of each land cover were obtained for the four different years i.e. 1989, 1997, 2008 and 2018 and found that the bare land and built-up land covers shows higher LST values as compared to the mean LST of entire area revealing positive contribution towards UHI
Summary
Urban heat island (UHI) is a phenomenon which may have adverse effects on our environment and is stimulated as a result of urbanisation or land cover changes. In the recent past few decades, urbanisation has increased as a consequence of rapid population growth which led to adverse effect on our environment. People’s migration from rural to urban areas is the major cause for urbanisation or growth in the urban sprawl at a large extent due to the increased human activity in the cities. This account for the land-use and land-cover (LULC) shift from natural land to impervious surface, transportation, industry modifies the thermal conduction with the environment. The impervious land like buildings, roads etc. have higher thermal capacity which captivates heat during day and releases during night
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