Urban heat island (UHI) is a specific area, generally in urban regions where the environment is much hotter than the nearby rural areas because of human activities and increase in impervious surface. Human initiated land use/land spread changes bit by bit extending the impenetrable surface in the types of buildings and road network during the urbanization.
This adjustment in the surface materials and land utilization of the city regions impact nearby temperatures and make urban territories hotter than the encompassing non-urbanized regions.
High surface temperature affects the local climate and public health and consumes more energy for air-conditioning or refrigeration. It is not a direct indication of global warming but urbanization, forestation and green building technology may be directly related research topics.
Land Surface Temperature (LST):
It is a general climate variable, which refers to the temperature measured in the air close (1 m) to the earth surface in an open area. It is applicable to any place. The LST of a place is the indicator of its climate change and radiation exchange with atmosphere.
It is important for meteorology, soil moisture and environmental studies. LST is the minimum, average / mean, and maximum temperature of the surface areas.
Therefore, mapping change in LST plays an important role in local and regional environment condition of the city. Introduction of thermal remote sensing technology has offered prospects for gaining information at various spatial goals and inclusion of earth surface.
Land Surface temperature is determined utilizing thermal band of satellite information and gives basic and valuable data of LST patterns and it’s interrelationship with surface qualities.
There are numerous methods to measure and investigate the surface temperature, for this several algorithms such as split-window, dual angle and single-channel are available to estimate the LST and to understand the influence of the characteristics of urban surfaces on UHI.
In the below example, image processing software used to create land use land cover map and Split window Algorithm was used to derive land surface temperature in GIS environment.
Land Surface Temperature can be calculated from At-Satellite Brightness Temperature (BT) as:
LST=BT/[1+(w * BT/C2)ln(e)]
Where, BT=at-sensor brightness temperature, w = wavelength of emitted radiance, C2 =1.4388×10-2mK, h=Plank’s constant i.e. 6.626×10−34 Js, s=Boltzmann constant (1.38 × 10−23J/K), c = velocity of light (2.998 × 108 m/s), e =Land Surface Emissivity (LSE).
Outcome of Land surface temperature shown in below figure:
Figure showing Land surface temperature of 1999
Figure showing Land surface temperature of 2016
Above two figures show the land surface temperature of 1999 and 2016, which is further categorized in to three class based on distance from city center using buffer tool of GIS. This way one can understand how temperature is changing, when moving away from built up area.
Surface temperature of the study area has increased by 4.4◦C during 1999 to 2016. Thus, increase in non-evaporating surfaces such as settlement, bare soil and rocky land have contributed to increase in land surface temperature of the study area.