AEGAEUM JOURNAL ISSN NO: 0776-3808
Urban Heat Island Phenomenon - A Case Study of Nashik
Akash Bhamare1 & Shishir Dadhich2 1PG student in Town & Country Planning, Department of Civil Engineering, SOET, Sandip University, Nashik, Maharashtra, India. 2Assistant Professor in Town & Country Planning, Department of Civil Engineering, SOET, Sandip University, Nashik, Maharashtra, India. Email-Id: [email protected],[email protected]
Abstract: Urban heat islands are areas in cities having a higher temperature than their surrounding rural areas. Urbanization has led to an increase in the impervious surface and increases anthropogenic heat causing warming of the urban area. Rapid urbanization is seen in Nashik with a nearly twofold increase of urban population. UHI intensity of Nashik was studied using Landsat 8 imagery and ArcGIS software. LST was calculated using NDVI and emissivity values obtained using ArcGIS and Landsat 8 data. UHI intensity of 5.7oC was found in the study area. Maximum LST observed in Nashik was 44.5oC. 52.5% of the study area was found to be lying between 36-39oC surface temperature range. Keywords: Remote Sensing, Land Surface Temperature, Urban Heat Island, Urbanization, Urban Heat Island Intensity
1. Introduction Industrialization and urbanization are responsible for increasing population in urban areas. In 2018, 55% of the world’s population was living in urban areas. 416 million urban dwellers are estimated for India during 2018 and 2050 [3]. During 2018 and 2050, growth of 416 million urban populations is estimated for India [3]. Urbanization is the major factor causing global warming. Due to urbanization, cities are growing in size leading to the expansion of built- up area and impervious surfaces at the cost of reduction of natural surfaces. Cities affect the energy balance of the earth and result in raising the temperature of urban areas. Variation in urban and the temperature of their rural surrounding is observed throughout the world by different researchers. Luke Howard was the first to observe that air temperatures in cities are higher than their rural surroundings. Manley defined this difference as an urban heat island (UHI). UHI is closely related to human comfort and quality of life. UHI has an adverse impact on the environment and human health. UHI is dependent on many factors such as anthropogenic heat, built-up density, city size, land use type, urban geometry, urban materials, weather, the topography of the area etc. UHI has adverse impacts like increased air pollution, frequency of heatwaves, mortality rate, thermal comfort, diseases and epidemics etc. UHI can be differentiated in two types – Atmospheric UHI (AUHI) and Surface UHI (SUHI). Atmospheric UHI is generally measured using data from meteorological stations and traverse survey. Surface UHI is measured using remote sensing. Remote sensing data provide continuous coverage over a large area and real-time data acquisition is also possible. Remote sensing can provide data with high temporal and spatial resolution. SUHI studies are successfully carried out throughout the world.
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In AUHI air temperature is considered for identification similarly for SUHI, land surface temperature (LST) is an important parameter used for identification of UHI. Land surface temperature (LST) can be defined as a radiative temperature of the earth’s surface. LST is calculated using thermal bands of satellite imagery. In this study, Landsat 8 satellite data is used. 1.1 Objectives: The study aims to determine UHI intensity for Nashik city by following objectives to persuade the aim are: To calculate the Normalized Difference Vegetation Index (NDVI) To calculate LST To calculate UHI intensity
2. Study Area Nashik city has a mythological, socio-cultural and historical importance. Nashik is known as grape city or wine city. The Nashik Municipal Corporation area is lying between 19o 55’ and 20o 05’ North Latitude and 73o 41’ and 73o 54’ East Longitude. It is situated on the eastern slope of the north-south of Sahayadri ranges. The Nashik Municipal Corporation covers an area of about 267.48 square kilometres (26747.75 hectares) and includes 25 villages. Two rivers, river Godavari and river Nasardi flow through the centre of the city in the west-east direction. River Darna forms the southern boundary of the Corporation area to which river Waldevi flowing through the southern part of the area, meets near Chehedi.
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Figure 1. Study Area- Nashik 3. Methodology 3.1 Data: For this study, Landsat 8 satellite image of 5th May 2019 was used. It was obtained from the USGS website. ArcMap software was used for satellite image processing. Band 4 (Red), Band 5 (NIR), Band 10 & 11 (TIRS) bands were used for analysis. Landsat level 1- L1TP data product was used. Atmospheric correction of the bands was done. LST was retrieved using the following methodology:
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Figure 2. Methodology for LST retrieval 3.2 Process: 1. Top of Atmosphere (TOA) Radiance:
= ∙ + where: = Spectral radiance (W/ (m2 * sr * μm))
= Radiance multiplicative scaling factor for the band (RADIANCE_MULT_BAND_n from the metadata)
= Radiance additive scaling factor for the band (RADIANCE_ADD_BAND_n from the metadata)
= Level 1-pixel value in DN 2. Top of Atmosphere (TOA) Brightness Temperature: This is the effective at-satellite temperatures of the viewed Earth-atmosphere system under an assumption of unity emissivity and using pre-launch calibration constants listed in Metadata. The conversion formula is: = + 1 where:
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T = Top of atmosphere brightness temperature (K) K1 = Band-specific thermal conversion constant from the metadata (K1_CONSTANT_BAND_x, where x is the thermal band number) K2 = Band-specific thermal conversion constant from the metadata (K2_CONSTANT_BAND_x, where x is the thermal band number) 3. Normalized Differential Vegetation Index (NDVI): The Normalized Differential Vegetation Index (NDVI) is a standardized vegetation index which Calculated using Near Infra-red (Band 5) and Red (Band 4) bands. NDVI = (NIR – RED) / (NIR + RED) Where: RED= DN values from the RED band NIR= DN values from Near-Infrared band 4. Land Surface Emissivity (LSE): Land surface emissivity (LSE) is the average emissivity of an element of the surface of the Earth calculated from NDVI values. PV = [(NDVI – NDVI min) / (NDVI max + NDVI min)]2 Where: PV = Proportion of Vegetation NDVI = DN values from NDVI Image NDVI min = Minimum DN values from NDVI Image NDVI max = Maximum DN values from NDVI Image Emissivity was calculated using the equation provided by [5]: E = 0.004 * PV + 0.986 Where: E = Land Surface Emissivity PV = Proportion of Vegetation 5. Land Surface Temperature (LST): The Land Surface Temperature (LST) is the radiative temperature Which calculated using Top of atmosphere brightness temperature, Wavelength of emitted radiance, Land Surface Emissivity. LST = (T / (1 + (W * (T / 14380) * ln(E)))
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Where: W = Wavelength of emitted radiance 6. Urban Heat Island Intensity (UHI): UHI was calculated using the following method: = + 2 Where: = Mean LST value of the area, = Standard deviation of LST.
4. Results
NDVI maps show that NDVI values ranged between -0.17 to 0.76. The land surface map has been derived using brightness temperature and LSE. Results from
Figure 4. LST Map
Figure 3. NDVI Map
land surface temperature analysis showed that minimum and maximum temperature in the study area were 30oC & 45oC with a mean temperature of 38oC. Maximum UHI intensity of 5.7oC was observed from the analysis. UHI Area of 85.20 square kilometres was found in the study area of 267. 48 square kilometres.
Table 1. Temperature Classes Temperature Area % and areas 30-33 3.1194 1.16% 33-36 47.2068 17.56%
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AEGAEUM JOURNAL ISSN NO: 0776-3808
36-39 141.1686 52.50% 39-42 75.1356 27.94%
42-45 2.2581 0.84% Total 268.8885 100.00%
Figure 5. UHI Map
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Conclusion:
NDVI, LST and UHI map for the study area were determined using ArcGIS. UHI intensity of 5.7oC was found in Nashik city. The maximum surface temperature was 44.5oC. LST values reveal that 52.50% of the study area, the surface temperature lies in the range of 36-39oC and 27.94% area lies in the range of 39-42oC.
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