Introduction
Urbanisation is a form of metropolitan growth that is a response to often bewildering sets of
economic, social, and political forces and to the physical geography of an area. It is the increase
in the population of cities in proportion to the region’s rural population. The 20th century is
witnessing “the rapid urbanisation of the world’s population”, as the global proportion of
urban population rose dramatically from 13% (220 million) in 1900, to 29% (732 million) in
1950, to 49% (3.2 billion) in 2005 and is projected to rise to 60% (4.9 billion) by 2030 (UN,
2005). Urban ecosystems are the consequence of the intrinsic nature of humans as social
beings to live together (Sudhira et al., 2003; Ramachandra and Uttam Kumar, 2008). The
process of urbanisation contributed by infrastructure initiatives, consequent population growth
and migration results in the growth of villages into towns, towns into cities and cities into
metros. Urbanisation and urban sprawl have posed serious challenges to the decision makers
in the city planning and management process involving plethora of issues like infrastructure
development, traffic congestion, and basic amenities (electricity, water, and sanitation), etc.
(Kulkarni and Ramachandra, 2006). Apart from this, major implications of urbanisation are:
- Loss of wetlands and green spaces: Urbanisation has telling influences on the natural
resources such as decline in green spaces including wetlands and / or depleting
groundwater table.
- Floods: Common consequences of urban development are increased peak discharge and
frequency of floods as land is converted from fields or woodlands to roads and parking lots,
it loses its ability to absorb rainfall. Conversion of water bodies to residential layouts has
compounded the problem by removing the interconnectivities in an undulating terrain.
Encroachment of natural drains, alteration of topography involving the construction of
high rise buildings, removal of vegetative cover, reclamation of wetlands are the prime
reasons for frequent flooding even during normal rainfall post 2000.
- Decline in groundwater table: Studies reveal the removal of waterbodies has led to the
decline in water table. Water table has declined to 300 m from 28 m over a period of 20
years after the reclamation of lake with its catchment for commercial activities. Also,
groundwater table in intensely urbanized area such as whitefield, etc. has now dropped
to 400 to 500m.
- Heat island: Surface and atmospheric temperatures are increased by anthropogenic
heat discharge due to energy consumption, increased land surface coverage by artificial
materials having high heat capacities and conductivities, and the associated decreases
in vegetation and water pervious surfaces, which reduce surface temperature through
evapotranspiration.
- Increased carbon footprint: Due to the adoption of inappropriate building architecture,
the consumption of electricity has increased in certain corporation wards drastically. The
building design conducive to tropical climate would have reduced the dependence on
electricity. Higher energy consumption, enhanced pollution levels due to the increase of
private vehicles, traffic bottlenecks have contributed to carbon emissions significantly. Apart
from these, mismanagement of solid and liquid wastes has aggravated the situation.
Unplanned urbanisation has drastically altered the drainage characteristics of natural
catchments, or drainage areas, by increasing the volume and rate of surface runoff. Drainage
systems are unable to cope with the increased volume of water and are often encountered
with the blockage due to indiscriminate disposal of solid wastes. Encroachment of
wetlands, floodplains, etc. obstructs floodways causing loss of natural flood storage.
Damages from urban flooding could be categorized as: direct damage – typically material
damage caused by water or flowing water, and indirect damage – e.g. traffic disruptions,
administrative and labour costs, production losses, spreading of diseases, etc.
Studies on the phenomenon of Urban Heat Island (UHI) using satellite derived land
surface temperature (LST) measurements have been conducted using various satellite
data products acquired in thermal region of the electromagnetic spectrum. Currently
available satellite thermal infrared sensors provide different spatial resolution and
temporal coverage data that can be used to estimate LST. The Geostationary Operational
Environmental Satellite (GOES) has a 4-km resolution in the thermal infrared, while the
NOAA-Advanced Very High Resolution Radiometer (AVHRR) and the Terra and Aqua-MODIS have 1-km spatial resolutions. Significantly high resolution data come from the
Terra-Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)
which has a 90-m pixel resolution, the Landsat-5 Thematic Mapper (TM) which has a
120-m resolution, and Landsat-7 Enhanced Thematic Mapper (ETM) which has a 60-m
resolution. However, these instruments have a repeat cycle of 16 days (Li et. al., 2004;
Ramachandra and Uttam Kumar, 2009). Weng (2001, 2003) examined LST pattern and its
relationship with land cover (LC) in Guangzhou and in the urban clusters in the Zhujiang
Delta, China. Nikolakopopulos et al., (2003) have used Landsat-5 TM and Landsat-7
ETM+ data for creating the temperature profile of Alfios River Basin. Stathopoulou and
Cartalis (2007) have used Landsat ETM+ data to identify daytime urban heat island using
Corine LC data for major cities in Greece. Using a Landsat ETM+ imagery of City of
Indianapolis, IN, USA, Weng et al., (2004) examined the surface temperature UHI in the
city. They derived LST and analysed their spatial variations using Landsat ETM+ thermal
measurements with the urban vegetation abundance and investigated their relationship.
UHI studies have traditionally been conducted for isolated locations and with in situ
measurements of air temperatures. The advent of satellite remote sensing technology has
made it possible to study UHI both remotely and on continental or global scales (Streutker,
2002). In this work, Landsat data of 1973 (of 79 m spatial resolution), 1992 and 2000 (30
m), IRS LISS-III data of 1999 and 2006 (23.5 m) and MODIS data of 2002 and 2007
(with 250 m to 500 m spatial resolution) are used with supervised pattern classifiers based
on maximum likelihood (ML) estimation. Also, an attempt is made to map land surface
temperatures across various LC types to understand heat island effect.
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