Managing Natural Disasters in Coastal Areas- an overview
S K Srivastav
President, CIMO & Addl. Director General of Meteorology, India Meteorological Department
Introduction
Natural disasters are events caused by the forces of nature that adversely effect
on human settlements, and environment. The coastal zone is the transitional area
between land and sea. It is defined, as a strip of land and sea of varying width
depending on the nature of the environment and management needs. It seldom
corresponds to existing administrative or planning units. The natural coastal systems
and the areas in which human activities involve the use of coastal resources may
therefore extend well beyond the limit of territorial waters and many kilometres inland.
The worldwide average width of the coastal zone on the terrestrial side is said to be 60
km. The zone occupies less than 15% of the Earth's land surface, yet it accommodates
more than 60% of the world's population. Furthermore, only 40% of the one million-km of
coastline is accessible and temperate enough to be habitable. As a result, coastal zones
are marked by above-average concentrations of people and economic activity. This
coupled with their proximity to the ocean makes them one of the most sensitive zones
for natural disasters. In the future, it is estimated that about 600 million people will
occupy coastal flood plain land below the 1000-year flood level by 2100 (Nicholls and
Mimura (1998).
Every year natural disasters result in considerable damages to life and property
not only in the coastal zones but also in other vulnerable areas. 2001 has been a year of
average losses, as compared to 1999 with record number and 2000 with few losses.
Figure 1 gives the numbers of natural disasters and their damage estimates. As coastal
zones are more prone to natural disasters there must be better management policies to
adjust and cope with such events. In most countries throughout the World, coastal zone
management has traditionally been practiced in a sectoral fashion, based upon political
or socio-economic boundaries. More recently, the concept of Integrated Coastal Zone
Management (ICZM) has led to the idea that coastal zones would be more effectively
and efficiently managed on the basis of information inputs from various sectors including
improved weather warning and management systems. Remote sensing, Geographical
Information Systems (GIS) and the Information Technology offer potential solutions for
ICZM. Remote sensing has, for a long time, been an invaluable source of environmental
data and information. It has many advantages, including the capability to collect data
over large tracts of land at any one time, and at a range of scales, from low-resolution
data covering large areas, to high-resolution data covering smaller areas. Moreover,
remote sensing provides a unique ability to collect both terrestrial and marine data in one
seamless dataset. With the vast amount of data available about the coast, and with the
potential to add even more data into the system (including remotely sensed imagery,
and online GIS), there also needs to be a new, more simple, but also more effective way
of gaining quick and easy access to this data and information.
Figure 1. Natural disasters – numbers and their damage estimates during the
years (Topics 2001, Annual Review: Natural Catastrophes in 200 by Munich Re
Group)
Potential Natural Hazards to Coastal Zones
There are a wide variety of meteorological phenomena, which pose a threat to
the coastal zones. They could be roughly listed the following:





Floods/flash floods, cloud burst, heavy precipitation
Tropical cyclones and their associated storm surges
Severe convective storms - thunderstorms, hailstorms, tornadoes,
lightening, dust storms, sand storms
Heat wave and cold wave
Snow avalanches
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
Sea erosion
The spatial and temporal scales of these hazards vary widely from short-lived, violent
phenomena of limited extent (e.g. severe thunderstorms), through large systems (e.g.
tropical cyclones). These events can subject large regions to disastrous weather
phenomena like strong winds, heavy flood-producing rains, storm surges and coastal
flooding, heavy snowfall, blizzard conditions, freezing rain and extreme hot or cold
temperature conditions for periods of several days. With this wide variety of the scales of
weather phenomena, the requirements of meteorological and hydrological forecasting for
effective early warning of these hazards also vary spanning over a very broad spectrum.
These can range from very short range forecasts of less than one hour in the case of
severe thunderstorms and flash floods; through short and medium range forecasts of
from a few hours to days for tropical cyclones, heavy rains, extreme temperatures and
high winds.
The various natural hazards pertaining to coastal zones can be summarized as
below:
Meteorological
(M)
Hydrological
(H)
Geological
(G)
Human Activity
Induced
(A)
Cyclone
Wind Damage
Severe Thunderstorm
Heat & Cold Waves
Heavy Rainfall
Urban Floods
Drought
Volcano
Srorm Surge
Earthquakes
Floods
Tsunami
Chemical Leak
Climate Change
Air Pollution
(Oil Spills)
Salinization
Siltation
Water Pollution
Tropical cyclones
Tropical cyclones are intense vortices in the atmosphere with strong winds
circulating anti-clockwise around a low-pressure area in the Northern Hemisphere and
clockwise in the Southern Hemisphere. They are capable of causing massive destruction
in three ways: by high winds; heavy rainfall causing inland flooding; and storm surge
inundating low lying areas. Tropical cyclones form in the warm tropical oceans where the
sea surface temperature is at least 26.5 C. They may last with destructive power for two
weeks or more where a large open sea is available. The storm surges are by far the
greatest killers in a cyclone. The Bay of Bengal region has the distinction of having
experienced the world’s highest recorded storm tide of 41 feet (1876 Bakerganj cyclone
near Megna estuary, Bangladesh). As a result of storm surge, sea water inundates low
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lying areas of coastal regions causing heavy floods in the coastal areas, eroding
beaches and embankments, destroying vegetation and reducing soil fertility. Very strong
winds may damage overhead installations, dwellings, communication systems, trees
etc., resulting in loss of life and property. Flood and tidal waves due to storm surges
pollute drinking water sources resulting in shortage of drinking water and causing outbreak of epidemics, mostly water borne diseases. Past records show that very heavy
loss of life due to tropical cyclones have occurred in the coastal areas.
Floods
Floods are excessive accumulation or flows of water, which result from heavy
rainfall. They include flash floods, which are caused by rapidly rising and falling rivers
and overland flows resulting from the rapid run-off of intense rainfall from upland areas
(usually hilly upstream); river floods in which river water spills over adjoining land;
rainwater floods from the ponding of rainfall run-off and the raised ground water-table
flood plain depression; tidal flooding, usually saline from the outflow of coastal rivers at
high tides; and storm surge floods associated with the passage of tropical cyclones.
Excessive runoff from the catchment due to heavy rainfall, concentrated in short
time periods resulting in the spilling over the banks of the river channel may be due to
inadequate channel capacity.
Heavy sediments brought from the catchments are
deposited on the riverbed reducing the channel capacity thereby increasing the flood
risk, Breaching of embankments/failure of a dam results in flood inundation. Human
interference with the floodplain disturb the flow regime and increases the flood risk, The
drainage congestion caused by natural processes and human activities further
aggravates the flood problem.
Climate Change and sea-level rise
Many coastal areas are already experiencing coastal erosion, sea-water intrusion
and sea-flooding. The increased sea-levels due to climate change may aggravate these
problems. Productive coastal ecosystems, coastal settlements and islands will be
vulnerable to these pressures. Tropical and sub-tropical coastlines, which are under
significant population pressures, will be significantly impacted by these changes.
Salinization of potable ground water, inundation of coastal zone and erosion will be
exacerbated. Climate change will also directly impact coastal wetlands, especially
mangroves, coral reefs, lagoons and estuaries. Large scale bleaching of corals has been
already reported. The extent of impacts will depend on the rate of sea-level rise. Strict
protection; preparation of action plan for each component, regeneration, and providing
space for backward movement of species are some mitigating measures.
Effects of climate change on coastal has been mostly considered from the
standpoint of sea-level rise. Increase in air-sea and sea-surface temperatures, changes
in wave characteristics, storminess and tidal regions will also impact coastal zones. Sealevel rise will impact the low-lying areas such as deltas and coastal plains. More severe
storm-surge flooding, saltwater intrusion and sedimentation will be some of the potential
impacts of climate change on coastal areas.
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Tsunami
Tsunami’s (Japanese for "harbor wave”), are large waves generated by
earthquakes, landslides, volcanic eruptions, explosions, and even the impact of cosmic
bodies, which can savagely attack coastlines, causing devastating property damage and
loss of life. Coastal zones are always prone to such tsunami hazards caused by natural
phenomena occurring at regions far removed from the actual coastal zone. Although,
tsunami is sometimes referred to as "seismic sea wave" because of its frequent
association with an earthquake it can also be caused by a non-seismic event, such as a
landslide or meteorite impact.
Tsunamis are characterized as shallow-water waves, with long periods and wave
lengths. They are often observed with wavelengths in excess of 100 km and period on
the order of one hour. Due to their large wavelengths, tsunamis propagate at high
speeds, great transoceanic distances with limited energy losses. As a tsunami
approaches shore, it begins to slow and grow in height. They inundate and flood
hundreds of meters inland past the typical high-water level, damaging homes and other
coastal structures. Despite energy losses on approaching shore, tsunamis still reach the
coast with tremendous amounts of energy with great erosional potential, undermining
trees and other coastal vegetation.
Observational aspects
Surface weather
A dense network of observations is required to assess and mitigate weatherrelated hazards to the coastal zone. Also, ocean based data collections through buoys is
necessary. Installation of Automatic Weather Stations over coastal areas will immensely
help monitoring and warning coastal zones about hazardous weather. It is important to
consider the topography and vulnerability of the coastal zone to severe weather before
deciding on the weather station network requirements. The network should also be
capable of disseminating the weather data collected on real time basis for use in
forecasting offices. This will enable quick diagnosis and planning of mitigative
measures. Severe weather systems affecting coastal areas mostly have their origins in
the seas and oceans adjoining the coast. It is therefore necessary to enhance the data
collection efforts over the oceans. Although space based and remotely sensed data is
available is important to have actual observation at the surface. Ship observations and
data from ocean buoys are crucial while decisions are taken on track forecasts of
storms. Both in-situ and remote sensing techniques have been evolving during recent
past. Automatic Weather Stations (AWS) and Automatic Weather Systems (AWSs)
have taken an operational status in some of the important development in Ground Based
Remote Sensing Techniques. The monitoring system for specific type of natural disaster
need a combination of several techniques as some of these pointedly observe whereas
some others provide supporting observation to evolve warning mechanisms. This needs
high degree of expertise and investment.
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Satellite observations
Satellite measurements systems have been continually evolving to enable better
monitoring of synoptic systems over the oceanic regions adjacent to coastal areas.
Satellite based systems are used to obtain both images and quantitative information
about meteorological features of the lowest 20 km of the atmosphere. Space-based
observations together with surface-based networks provide invaluable monitoring of
weather and climate, providing prior information on natural hazards. Since the 1960s,
when the first weather satellites were introduced, the space-based observational
systems have evolved substantially. They have been particularly useful in monitoring
coastal zones and biological activity as well as weather hazards associated to coastal
zones.
Doppler Radar and other Radar networks
Radar observations are very useful in detection and monitoring severe weather,
which could be potentially disastrous. Since there is a wide range of weather
phenomena, a variety of radar characteristics are used according to requirements. A
reliable radar network can provide adequate means for monitoring severe weather over
a large stretch of coastal zone. The present generations of Doppler radars, which can
identify and provide a measure of intense winds associated with tropical storms and
thunderstorms downbursts, have enhanced our capabilities. Radars can also provide
good description of heavy precipitation associated with mesoscale weather systems
often encountered in coastal areas with topography. Optimal network of radars can
therefore help in monitoring hazardous weather capable of damaging effects on coastal
zone. Figure 1 shows a Doppler radar image of a weather system over the southeastern
coast of India.
Figure 1. A typical PPI (Z) of a weather system over Southeast coast of India.
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Monitoring System for Coastal Hazards
1.
For effective monitoring and early warning about coastal zone natural hazards
there should be an integrated monitoring system. The system will incorporate latest
technologies of meteorological instruments coupled with suitable networking
mechanisms and dissemination system. The systematical diagram below illustrates the
components of such a system.
Coastal Zone Monitoring System
Monitoring System
(Land)
Surface
Meteorological
Remote
Space
Based
Ground Based
Automatic Weather Stations
Sodar (Doppler)
AVHRR
Lidars
Water Vapour
High Response Raingauges
Wind Profilers
CCD Camera
Disdrometers
Doppler Radars
High resolution GPS Radiosonde
Mesoscale Observation Stations
Microwave
Radiometer
GPS Occultation
From Water Vapour
LWS
Advance Lightning
Detection System
High Resolution Camera
for
Land Images
Quantitative
Precipitation
Multi Channel SST
ATOVS
Microwave
Sensing
TRMM
Colour Monitoring
Multiscanning
TOMM and other Ozone
Measuring Payload
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2.
It is imperative from coastal zone management that the integrated observations,
both from land and sea, should be evaluated. The monitoring of sea state and other
parameters is a complex, logistically difficult and expensive proposition. Sea platforms
like the data buoys, instruments on board ships, etc. need to be deployed supplemented
with merchant navy ships. Recent development of polar orbit satellites has unanimously
complemented with inaccessible data sets. However, standardization and calibration of
weather parameters yet remains a problem. Development of new techniques like ARGO
floats are providing very useful means in collection of valuable sub-surface sea data.
Consolidated efforts are required to homogenize the entire land and sea data in order to
make best use in Atmosphere – Land – Ocean coupled models to evolve a reliable
forecasting system.
Monitoring System
(Ocean)
Surface
Date buoy Parameters:

Pressure,

Temperature

Relative Humidity

Winds

Sea Surface Temperature

Salinity

Precipitation

And Tidal Winds etc.
Instrumented ships Parameters:

Salinity

Temperature Profile

XBT

Radiosondes etc
Remote
Radar Products:

Storm Surge

Winds

Precipitation
Satellites:

Ocean Colour

Tidal Waves

Surface Winds

SST

Water Vapour

Precipitation
Merchant Ship for surface Parameters:
ARGOs Parameters:

Ocean Current

Temperature

Salinity
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Integrated Management Strategies for Coastal Zone
Integrated management strategies to ensure safety against natural hazards such
as high waves, storm surges, and tsunamis have to be evolved and operationalized. In
urbanized coastal zone vulnerability of support systems like waste management
facilities, water supply and roads need to be taken into account. Disaster prevention
facilities along the coast may have to be strengthened keeping in view present and
potential (including those due to climate change) damage threats. Increased water table
due to sea-level rise may weaken coastal structures and predispose them to other
natural hazards like earthquakes and storm related damages. If we carefully examine
the process of risk reduction we arrive to the following five basic steps:






Evolving efficient monitoring and surveillance system
Evolving accurate early warning systems
Putting in places an efficient warning dissemination system
Evolving pre-disaster hazard, vulnerability and risk assessment inventories
Evolving efficient post-disaster management and mitigation strategy.
Public Awareness.
In addition to conventional techniques, a number of new techniques have
emerged in the recent past in the area of whether and climate monitoring. Evaluations
of high-resolution area specific models have been developed. Their operational uses
have become possible due to high-speed bulk data crunching computers available at
lower prices. Thus, in addition to surveillance system have provided effective tool in
providing early warning for some of the natural disaster effective. Rapid strides in
satellite communication have resulted into fail-safe warning dissemination system. The
technological interventions are showing the results for evolving effective meteorology’s
for risk assessment and management during pre and post disaster periods. However,
this area is still in evolution phase and lot of work needs to be done.
Availability of advance computer and development of software technologies have
allowed rapid strides to management strategies of natural disaster. Multi-LayerGeographical Information System (GIS) has emerged as most handy tool for effective
management in different phases of disaster. However, these technologies are still in
evolution phase and adoption in developing countries needs to be encouraged.
In summary, there is a strong need for integrating physical impacts and
socioeconomic implications in the coastal zone. Both evolving integrated observational
network and disaster management planning is an inter-disciplinary, inter-commissional
issue. Thus, there is also a growing need for emphasis on effectively bringing together
researchers, policymakers, other stakeholders and resident communities and creating a
framework that integrates into the current coastal management procedures.
References
Munich Re, 2000: Topics—Annual Review of Natural Disasters 1999 (supplementary data and
analyses provided by Munich Reinsurance Group/Geoscience Research Group,
MRNatCatSERVICE). Munich Reinsurance Group, Munich, Germany, 46 pp.
Nicholls, R.J. and Mimura, 1998: Regional issues raised by sea-level rise and their policy
implications, Climate Research, 11(1), 5-18.
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