 |
Indian coastline stretches about 5700 kms on the mainland
and about 7500 kms including the two island territories
and exhibits most of the known geomorphological features
of coastal zones. Presently, Indian coastline is facing
increasing human pressures e.g., overexploitation
of marine resources, dumping of industrial and toxic
wastes, oil spills and leaks which have resulted in
substantial damage to its ecosystems. The impact of
global warming-induced sea level rise due to thermal
expansion of near- surface ocean water has great significance
to India due to its extensive low-lying densely populated
coastal zone. Sea level rise is likely to result in
loss of land due to submergence of coastal areas,
inland extension of saline intrusion and ground water
contamination and may have wide economic, cultural
and ecological repercussions. Observations suggest
that the sea level has risen at a rate of 2.5 mm year
-1 along the Indian coastline since 1950s. A mean
sea level rise of between 15 and 38 cm is projected
by the mid- 21 st century along India’s coast.
Added to this, a 15% projected increase in intensity
of tropical cyclones would significantly enhance the
vulnerability of populations living in cyclone prone
coastal regions of India. Other sectors vulnerable
to the climate change include freshwater resources,
industry, agriculture, fisheries, tourism and human
settlements. Given that many climate change impacts
on India’s coastal zone feature irreversible
effects, the appropriate national policy response
should enhance the resilience and adaptation potential
of these areas.
India has been identified as one amongst 27 countries
which are most vulnerable to the impacts of global
warming related accelerated sea level rise (UNEP,
1989). The high degree of vulnerability of Indian
coasts can be mainly attributed to extensive low-lying
coastal area, high population density, frequent occurence
of cyclones and storms, high rate of coastal environmental
degradation on account of pollution and non-sustainable
development. Most of the people residing in coastal
zones are directly dependent on natural resource bases
of coastal ecosystems. Any global warming-induced
climatic change
such as increase in sea surface temperature, change
in frequency, intensity or tracks of cyclones, sea
level rise may aggravate the potential risks to coastal
zones. The rise in sea level could result in the loss
of cultivable land due to inundation, salt water intrusion
into coastal ecosystems and into groundwater systems
and loss of terrestrial and marine biodiversity. In
this paper, an attempt has been made to assess the
vulnerability of various sectors of coastal zones
to the impacts of sea level rise and some suggestions
on response strategies and adaptation measures have
been outlined.
General Features of Indian Coastline
Indian coastline extends to about 5700 kms on mainland
and to about 7500 kms including two groups of islands.
Western coastline has a wide continental shelf having
an area of about 0.31 million km 2 which is marked
by backwaters and mud flats. East coast consists of
Tamil Nadu coast, Andhra coast, Orissa
coast and West Bengal coast, which is flat and deltaic
and rich in mangrove forests covering an area of about
1430 km 2. Mangroves are located all along estuarine
areas, deltas, tidal creeks, mud flats, salt marshes
and extend to about 6740 km 2 (about 7% of world’s
mangrove areas). Major estuarine areas located along
the Indian coasts extend to about 2.6 million hectares
(Gauda & Panigrahy, 1999).
Coral reefs are predominant on small islands in Gulf
of Kutch, Gulf of Mannar in Tamil Nadu and on Lakshadweeep
and Andaman and Nicobar groups of islands. Ecosystems
such as coral reefs, mangroves, estuaries and deltas
are rich in biodiversity which play a crucial role
in fishery production besides protecting the coastal
zones from erosion by wave action. India ranked 5
th
in fishery productivity in Asia in 1996 (Grainger
& Garcia, 1996). A total number of 11 major and
130 minor sea ports located in coastal zones are economic
engines of International and National Trade and Commerce
in India.
Factors Affecting Vulnerability of Indian
Coastal Zones
Anthropogenic/Socio-economic factors Coastal zones
in India are currently facing increasing stresses
and shocks as a consequence of cumulative environment
change driven by population growth, urbanisation,
industrial development, trade and capital flows, liberalisation
of transnational corporation activity and life style,
attitudinal changes and unsustainable growth leading
to degradation of coastal zones and ecosystems. A
large percentage of coastal population is directly
dependent on coastal and marine resources like mangroves
and other coastal vegetations, agriculture and fisheries
for their livelihood. Any impact to the coastal ecosystem
may affect the coastal population in almost every
sector of their lives. Exploration and exploitation
of oil and gas activities in the offshore regions
like Godawari, Krishna and Bombay have resulted in
pollution of coastal ecosystems. The problem of freshwater
is already acute in coastal regions of Tamil Nadu,
Gujarat, West Bengal and Orissa due to the over-extraction
of groundwater which has resulted in lowering of groundwater
table and salt water intrusion. The lowering of groundwater
table has also led to subsidense of coastal land causing
high relative sea level rise. Lagoons located across
the coastal regions of India tend to be decreasing
in area due to silting of sediments and plant growing.
Sea-level rise and reduction of river-borne sediments
will decelerate delta progradation and wetland renewal.
The rich biodiversity is seriously threatened by loss
of wetlands due to sea level rise.
As a result of major coral bleaching in 1998, many
reefs dominated by branching species in Indian Seas
have been severely damaged with high mortality of
these species. In coastal seas around Andaman Islands
of India, reef community structure has switched from
dominance by fast-growing branching species to monopolization
by the more physically rigorous and slow-growing massive
corals. Quarrying of coral reefs in Lakshdweep islands,
Gulf of Mannar in Tamil Nadu and Gulf of Kutch in
Gujarat for the manufacture of calcium carbonate and
construction purposes has exposed the coasts to the
eroding actions of the waves (Qasim, 1999). Mining
of monazite sands for extracting a number of rare
earth elements like ilmenite, zircon and rutile along
Kerala coast at levels below sea water has resulted
in submergence of land, salt water intrusion into
fresh water and erosion. Mining of cast iron ore along
Goa coast has led to the formation of acidic waste
lands making the land more vulnerable to the impacts
of sea level rise and erosion. The vulnerability of
coastal zones to an increasing range of stresses and
shocks are likely to be exacerbated by climate change.
Climate change
Future climate change and estimated sea level rise
on Indian coastal zone Past observations on the mean
sea level along the Indian coast indicate a long-term
rising trend of about 1.0 mm year -1 on an annual
mean basis. However, the recent data suggests a rising
trend of 2.5 mm year -1 in sea level rise along Indian
coastline. Model simulation studies based on an ensemble
of four A-O GCM outputs indicate that the oceanic
region adjoining the Indian subcontinent is likely
to warm up at its surface by about 1.5-2.0 o C by
the middle of this century and by about 2.5-3.5 o
C by the end of the century. The corresponding thermal
expansion related sea level rise is expected to be
between 15 to 38 cm by the middle of century and between
46 to 59 cm by the end of the century (Lal & Aggarwal,
2000). This simulated rise in sea level by 46 to 59
cm along Indian coastline is comparable with the projected
global mean sea level rise of 50 cm by the end of
this century and may have significant impact on coastal
zones of India.
Sea surface temperature and tropical cyclones
Global warming would result in an increase in sea
surface temperatures as a result of which changes
in the frequency, intensity or tracks in cyclones
hitting the coastal zones may take place. India is
frequently affected by tropical cyclones and storms
particularly during or around monsoon season. About
6.5%
(Neumann, 1993) of about world’s 80 tropical
storms (McBride, 1995) are formed annually in the
Indian ocean. Frequency of formation of cyclones is
5-6 times more in Bay of Bengal as compared to Arabian
Sea (IMD, 1979). Therefore, the east coast of India
(particularly the States of Andhra Pradesh, Orissa
and West Bengal) is more vulnerable than the west
coast to the fury of cyclones and massive damage of
life and property occurs almost every year. The number
of cyclones and depresssions formed per annum over
the Bay of Bengal, the Arabian Sea and land during
the last century along with the all-India mean temperature
annomalies for the same period.
10,000 and demonstrates the extreme significance of
impacts related to climate variability and extremes.
There have been a number of studies on the likelihood
of changes in the tropical storms in the event of
global warming (Knutson et al., 1999; Henderson-Sellers
et al., 1998; Royer et al., 1998 and Krishnamurti
et al., 1998). Some recent global climate model experiments
suggest a future decline in tropical cyclone frequency
(Royer et al., 1998). Although the studies carried
out so far are inconclusive on the likely changes
in frequency of cyclones with global warming, it is
almost certain that an increase in sea surface temperature
will be accompanied by a corresponding increase in
cyclone intensity. Recent studies suggest a possile
increase in cyclone intensity of 10-20% for a rise
in sea surface temperature of 2 to 4 o C. The impacts
of any increase in the frequency or intensity of cyclones
due to global warming and consequent sea level rise
could be disproportionately large not only in heavily
populated coastal areas but also in terms of the paralyzing
devastation in low income rural areas of India.
Storm surges are generated by the winds and the atmospheric
pressure changes associated with cyclones. At low
latitude land-locked locations such as Bay of Bengal,
tropical cyclones are the major cause of storm surges.
Amplification in storm surge heights should result
from the occurrence of stronger winds and low pressure
associated with more intense tropical storms. Thus,
an increase in sea surface temperature due to climate
change should lead to higher peaks of storm surges
and a greater risk of coastal disasters along the
east coast of India in the event of sea level rise.
Vulnerability Assessment
Land inundation and population affected Recent studies
on the potential impact of one meter sea level rise
along Indian coast provide an idea about the land
which could be inundated and the population that would
be affected provided no protective measures are taken.
It has been suggested that the total area of 5763
km 2 along the Coastal States of India i.e., 0.41%
could be inundated and almost 7.1 million i.e., 4.6
% of coastal population could be directly affected
(TERI, 1996). The most vulnerable areas along the
Indian coastline are the Kutch region of Gujarat,
Mumbai and South Kerala. Deltas of rivers Ganges (West
Bengal), Cauvery (Tamil Nadu), Krishna and Godawari
(Andhra Pradesh), Mahanadi (Orissa) and also the islands
of Lakshadweep Archipelago would be totally lost.
Vulnerability of the region can be assessed not only
in terms of physical exposure to sea level rise but
also in terms of the level of socio-economic development
of that region like population density, land uses,
level of infrastructure and other investments. From
a purely physical point of view, Gujarat and West
Bengal would be most affected since they stand to
lose the maximum land area to one meter sea level
rise. In terms of population, West Bengal, Maharashtra
and Tamil Nadu would be worst affected because of
their high population density. In terms of the fractional
area, Goa would be most affected as it would lose
almost 4.34 % of its total area.
Salt water intrusion and fresh water resources
and
agriculture
In the coastal regions of Tamil Nadu, salinity of
groundwater due to the intrusion of seawater into
the subsurface aquifer is a major problem (Subramanian,
2000). Due to excess withdrawal of groundwater, the
water table has fallen too far below thereby allowing
seawater to percolate. Similarly, in Gujarat due to
uncontrolled withdrawal of groundwater, the ground
water is becoming highly saline apart from the fact
that depth of the water table reaching at places beyond
200 meters (Subramanian, 2000). Coastal aquifer system
will be more contaminated with salinity bringing greater
complicacy to the problem of tapping usable groundwater
(Mohanty, 1990). In coastal regions of West Bengal
and Orissa, the problem of fresh water is fairly acute
because of the depth of water table and high cost
of lifting the same from the depth of 700-1000 meters.
The shallow salt water table often renders stored
water in ditches and ponds brackish and surface soil
saline. In view of this, only one kharif crop could
be possible (Jhingran, 1989). Tidal ingress and pushing
up of saline waters inland may extend by 35-50 kms
beyond the present limit (Mohanty & Ray, 1987)
and during storm conditions, the spread of salinity
in the low-lying agricultural lands may ruin the prospect
of crops. The potential impacts of one meter sea level
rise on the land uses affected in the Coastal States
in terms of the share of total land affected are shown
in (TERI, 1996). The cultivated land would be worst
affected by both inundation and intrusion due to rising
sea level.
Vulnerability of mangroves, coral reefs and
other
ecosystems
Intensive production systems and large scale facilities
used to raise high value shrimp, salmon and other
premium species has taken a heavy toll on coastal
habitats, with mangrove swamps in India being cleared
at an alarming rate. Coastal ecosystems like mangroves,
coral reefs provide natural protection to coasts by
dissipating considerable wave energy and hence only
smaller waves of moderate intensity reach the shore
and break. Coastal erosion is caused by forces of
nature but very often accentuated by anthropogenic
activities like making of structures on shores, removal
of the materials from the shores etc. The fishery
resources of India are being depleted by over fishing,
excessive use of pesticide, industrial pollution and
even construction of coastal structures. The loss
of inshore fish nursery habitats by coastal development,
and pollution from land-based activities cause significant
change to ecosystems supporting fisheries. The impact
of global warming on fishery will depend on the complicated
food chain, which could be disturbed by sea level
rise, change in ocean currents, and alteration of
the mixing layer thickness.
The rich biodiversity of the wetlands in India is
seriously threatened by loss of wetlands due to sea
level rise. India’s Sunderbans are highly vulnerable
to sea level rise since it will change the salinity
distribution and hence the productivity. The effect
of sea level rise will depend on the type of mangrove
forest, these may either keep pace with the rising
sea level rise or these may be submerged. Large scale
changes in species composition and zonation in mangrove
forests are also expected due to changes in sedimentation
and organic accumulation, nature of coastal profile
and species interaction.
Response Strategies and Adaptation options
The impact of sea level rise on Indian coastline could
be significant which is already under stress due to
unsustainable human activities. To devise appropriate
and effective response strategies, it is essential
to make vulnerability assessment studies at regional
and local levels. For this, all the factors related
to eustatic sea level rise, local hydrological, meteorological
and oceanographic changes, local compaction and tectonic
movements need to be considered. There is an urgent
need to make a systematic inventory on tidal gauge
measurements, mud flats and drifts, estuarine activities
and other socio-economic activities which are being
carried out in coastal zones. Efforts should be initiated
to protect the coastal zones form erosion, salt water
intrusion by judiciously choosing the hard (e.g.,
seawall, revetments, groins etc.) or soft structures(e.g.,
regeneration of natural protective systems like mangroves,
coral reefs or replenishment of sandy beeches). Coastal
zone management plan should also include research
and development activities for cost effective methods
for the protection of coastal lands. Rules and regulations
must be framed and enforced to have a control over
the developmental activities and to put restrictions
on seaward extrusion. Such tasks should produce a
mix of products and services from the available coastal
resources, which should enhance India’s coastal
resilience and facilitate adaptation.
