Disasters

UNIT 2: DISASTERS DUE TO CLIMATE CHANGESDr. Pranesh M. R., Dr. Shashi Shankar A., Mr. Prashanth J.

2.1 INTRODUCTION

A disaster is the impact of a natural or human-made hazard that negatively affects society or environment. The root of the word disaster ("bad star" in Greek) comes from an astrological idea that when the stars are in a bad position a bad event will happen.

Disaster is an event or series of events, which gives rise to casualties and damage or loss of properties, infrastructures, environment, essential services or means of livelihood on such a scale which is beyond the normal capacity of the affected community to cope with. Disaster is also sometimes described as a “catastrophic situation in which the normal pattern of life or eco-system has been disrupted and extra-ordinary emergency interventions are required to save and preserve lives and/or the environment”.

An environmental disaster is a disaster to the natural environment due to human activity, which distinguishes it from the concept of a natural disaster. It is also distinct from intentional acts of war such as nuclear bombings.

In contemporary academia, disasters are seen as the consequence of inappropriately managed risk. These risks are the product of hazards and vulnerability. Hazards that strike in areas with low vulnerability are not considered a disaster, as is the case in uninhabited regions.

Developing countries suffer the greatest costs when a disaster hits – more than 95 percent of all deaths caused by disasters occur in developing countries, and losses due to natural disasters are 20 times greater (as a percentage of GDP) in developing countries than in industrialized countries.

India being a developing country is vulnerable, in varying degrees, to a large number of disasters. More than 58.6 per cent of the landmass is prone to earthquakes of moderate to very high intensity; over 40 million hectares (12%) of its land is prone to floods and river erosion; close to 5,700 kms, out of the 7,516 kms long coastline is prone to cyclones and tsunamis; 68% of its cultivable area is vulnerable to droughts; and, its hilly areas are at risk from landslides and avalanches. Moreover, India is also vulnerable to Chemical, Biological, Radiological and Nuclear (CBRN) emergencies and other man-made disasters. Fig. 2.1 shows the Indian climatic risk map showing the different regions prone to different types of disasters. Disaster risks in India are further compounded by increasing vulnerabilities related to changing demographics and socio-economic conditions, unplanned urbanization, development within high-risk zones, environmental degradation, climate change, geological hazards, epidemics and pandemics. Fig. 2.2 shows the major disasters that occurred in India during 1980-2009.

Disasters due to climate changes Page 1

Fig. 2.1 India climatic disaster risk map

Fig. 2.2: Major disasters in India during 1980 to 2009


2.2 CLASSIFICATION OF DISASTERS

For more than a century researchers have been studying disasters and for more than forty years disaster research has been institutionalized through the Disaster Research Center. Many researchers reflect a common opinion when they argue that all disasters can be seen as being human-made, their reasoning being that human actions before the strike of the hazard can prevent it developing into a disaster. All disasters are, hence, the result of human failure to introduce appropriate disaster management measures. Hazards are routinely divided into natural or human-made, although complex disasters, where there is no single root cause, are more common in developing countries. A specific disaster may spawn a secondary disaster that increases the impact. A classic example is an earthquake that causes a tsunami, resulting in coastal flooding. Fig. 2.3 shows the different types of disasters. Disasters may be broadly classified into,

(1) Natural Disasters: A natural disaster is the consequence when a natural hazard (e.g., volcanic eruption or earthquake) affects humans. Human vulnerability, caused by the lack of appropriate emergency management, leads to financial, environmental, or human impact. The resulting loss depends on the capacity of the population to support or resist the disaster: their resilience. This understanding is concentrated in the formulation: "disasters occur when hazards meet vulnerability". A natural hazard will hence never result in a natural disaster in areas without vulnerability, e.g., strong earthquakes in uninhabited areas. The term natural has consequently been disputed because the events simply are not hazards or disasters without human involvement.

(2) Man-made Disasters: Disasters caused by human action, negligence, error, or involving the failure of a system are called man-made disasters. Man-made disasters are in turn categorized as technological or sociological. Technological disasters are the results of failure of technology, such as engineering failures, transport disasters, or environmental disasters. Sociological disasters have a strong human motive, such as criminal acts, stampedes, riots, and war.

Fig. 2.3: Flow-chart of classification of disasters


2.3 INDIAN MONSOON

In India, the word monsoon commonly refers to the system that visits the continent every year and gives us rain. The commencement of the ‘rainy season’ is associated with the onset of the monsoon and the end of the rainy season with the retreat of the monsoon. For the country as a whole, most of the rainfall occurs during the summer monsoon season June-September. The Indian atmosphere remains on loaded with monsoon throughout the year. The Arabs came to India as traders and named this seasonal reversal of the wind system as 'Monsoon'. The word monsoon is derived from the Arabic word 'Mausim' which means season.

2.3.1 The onset of the monsoon and withdrawal

Onset: Generally, the monsoon arrives at the southern tip of the Indian peninsular by the first week of June. Subsequently, it divides into two branches, viz. the Arabian Sea branch and the Bay of Bengal branch. The Arabian Sea branch reaches Mumbai about ten days later, i.e. around 10th of June. The Bay of Bengal rapidly advances and reaches Assam in the first week of June. The monsoon winds are then deflected by high mountains and move towards west over the Ganga plains. The Arabian Sea branch of the monsoon arrives over Surashtra-Kuchchh and central part of the country by mid-June. The Arabian Sea and the Bay of Bengal branches of the monsoon merge over the northwestern part of the Ganga plains. Delhi usually receives monsoon showers from the Bay of Bengal branch by the end of June. Western Uttar Pradesh, Punjab, Haryana, and eastern Rajasthan experience monsoon by the first week of July. The monsoon reaches Himachal Pradesh and the rest of the country by mid-July. Fig. 2.4 shows the monsoon onset map of India.

Withdrawal: Withdrawal or the retreat of the monsoon is a more gradual process. The monsoon begins to withdraw from the northwestern states of India by early September. The monsoon withdraws completely from the northern part of the Indian peninsular by mid-October. The monsoon withdraws from the rest by the country by early December. The islands receive the very first monsoon showers from the first week of April to the first week of May; progressively from south to north. The withdrawal of monsoon in the islands takes place from the first week of December to the first week of January. Fig. 2.5 shows the retreat of monsoon in India.

2.3.2 The Seasons

There are four main seasons in India, viz. the cold weather season, the hot weather season, the advancing monsoon and the retreating monsoon.

The Cold Weather Season (winter): The winter season begins from mid-November and stays till February; in northern India. December and January are the coldest months in the northern part of India. The temperature ranges between 10°-15°C in the northern plains, while it ranges between 24°-25°C in Chennai. The northeast trade winds prevail over the


country in this season. As these winds blow from land to sea, most parts of the country experience a dry season. The winter rainfall is in small amount but is very important for the rabi crop. The peninsular region does not get a well-defined winter because of the moderating influence of the sea.

Fig. 2.4: Monsoon onset map of India

Fig. 2.5: Retreating monsoon of India (As on 2013 December)


The Hot Weather Season (summer): The summer season is from March to May. During this period, the global heat belt shifts towards north because of the apparent northward movement of the sun. During summer, the temperatures rise and air pressure falls in the northern part of the country. Towards the end of May, an elongated low-pressure area develops in the region which extends from the Thar Desert in the northwest to Patna and Chhotanagpur in the east and southeast. Dust storms are very common in northern India during the month of May. This is also the season of localized thunderstorms; accompanied by violent winds, torrential downpours, and hail. Pre-monsoon showers are common towards the end of the summer season; especially in Kerala and Karnataka. They are often called ‘mango showers’ as they help in the early ripening of mangoes.

Advancing Monsoon (the rainy season): The rainy season begins from early June. The low-pressure condition over the northern plains intensifies at this time. It attracts the trade winds from the southern hemisphere. These south-east trade winds cross the equator and blow in a south-westerly direction to enter the Indian peninsula as the south-west monsoon. These winds bring abundant moisture to the subcontinent. The monsoon winds cover the country in about a month. The north-eastern part of the country receives the maximum rainfall of this season. Meghalaya receives the highest average rainfall in the world. Monsoon tends to have ‘breaks’ in rainfall; which means that there are wet and dry spells in between. These breaks in the monsoon are because of the movement of the monsoon trough. The trough and its axis keep on moving northwards or southward due to various reasons. The movement of the monsoon trough determines the spatial distribution of rainfall. The monsoon is famous for its uncertainties. It may cause heavy floods in one part of the country, and may be responsible for droughts in other part. Because of its uncertain behaviour, it sometimes disturbs the farming schedule in India. Fig. 2.6 shows the distribution of rainy season in India.

Retreating Monsoon (The Transition Season): During October-November, the sun apparently moves towards the south. During this period, the monsoon trough over the northern plains becomes weaker. The south-west monsoon winds weaken and start withdrawing gradually. The monsoon withdraws from the northern plains by the beginning of October. The retreat of the monsoon is marked by clear skies and rise in temperature. While day temperatures are high, nights are cool and pleasant. Humidity would still be present. High temperature and humidity, makes the weather quite uncomfortable during the day. This is commonly known as “October Heat”. The temperature begins to fall rapidly in northern India by the second half of October. The low-pressure conditions over northwestern India move to the Bay of Bengal by early November. This shift leads to cyclonic depressions over the Andaman Sea. These cyclones usually cross the eastern coasts of India and cause heavy and widespread rain. These cyclones may also arrive at the Coasts of Orissa, West Bengal and Bangladesh. These cyclones contribute to the bulk of the rainfall of the Coromandel Coast.


Fig. 2.6: Indian Seasonal Rainfall

2.3.3 Distribution of Rainfall

The western coast and northeastern India receive over 4000 mm of rainfall annually. The annual rainfall is less than 600 mm in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab. Rainfall is also low in the interior of the Deccan Plateau and east of the Sahyadris. The area around Leh also gets low rainfall. The rest of the country gets moderate rainfall. Snowfall is restricted to the Himalayan region.

2.4 FLOODS

Floods are natural phenomena which result from the precipitation and form an essential source of freshwater. In case of extreme precipitation, melting of snow, rise of groundwater, storm surges or tsunami, water flows beyond the normal limits of the water bodies, thereby causing flooding. Extreme flooding is the most taxing of water-related natural hazards to life forms, socio-economic activities, material assets, as well as cultural and ecological resources.

India is one of the most flood prone countries in the world. The principal reasons for flood lie in the very nature of natural ecological systems in this country, namely, the monsoon, the highly silted river systems and the steep and highly erodible mountains, particularly those of the Himalayan ranges. The average rainfall in India is 1150 mm with significant variation across the country. The annual rainfall along the western coast and


Western Ghats, Khasi hills and over most of the Brahmaputra valley amounts to more than 2500 mm. Most of the floods occur during the monsoon period and are usually associated with tropical storms or depressions, active monsoon conditions and break monsoon situations. Major flood prone areas in India are shown in Fig. 2.7.

Floods occur in almost all rivers basins in India. The main causes of floods are heavy rainfall, inadequate capacity of rivers to carry the high flood discharge, inadequate drainage to carry away the rainwater quickly to streams/ rivers. Ice jams or landslides blocking streams; typhoons and cyclones also cause floods. Flash floods occur due to high rate of water flow as also due to poor permeability of the soil. Areas with hardpan just below the surface of the soil are more prone to floods as water fails to seep down to the deeper layers.

Vulnerability to floods is mainly caused by the high population density, widespread poverty, unemployment, illiteracy, enormous pressure on rural land, and an economy traditionally dominated by agriculture. Children and women are particularly vulnerable. Eighty five percent of the deaths during disasters are of women and children (Centre for Research on the Epidemiology of Disasters, CRED 2000). Presently there is an inadequate level of protection in the country against floods. Though non-structural measures improve the preparedness to floods and reduce losses, the necessity of structural measures would always remain to reduce the extent of physical damage caused by floods.

There are many causes of flooding including, but not limited to the following:

(1) Seasonal Flooding: According to some scientists, the record floods of 1990 were caused by global warming, the theories that the earth’s atmosphere traps heat near the earth, slowly warming the earth. This greenhouse effect may have heated the water in the Gulf of Mexico, causing it to evaporate faster. With more water vapor in the lower atmosphere, small storms escalated into large systems with lots of moisture. If the global warming theory is correct, sea levels will rise three to five feet in 60 years. Coastal areas may be partially submerged underwater or easily flooded.

(2) Coastal Flooding: The earth has seven oceans that cover almost three-fourths of its surface. Naturally, wind and other events caused ocean water to sometimes overflow. When this happens, flooding on the shores occurs. Ocean storms can dump lots of water on a coast, raising the sea level in that area. These are known as storm surges, and cause coastal flooding.

Coastal flooding usually occurs as a result of severe storms, either tropical or winter storms. Ocean waves intensify on the open ocean, and these storms make surface water much choppier and fierce than normal. Raging winds can create huge waves that crash on unprotected beaches.


Fig. 2.7: Flood prone map of India

The effects of flooding can be divided into following categories:

2.4.1 Primary effects:

Physical damage- Can range anywhere from bridges, cars, buildings, sewer systems, roadways, canals and any other type of structure.

Casualties- People and livestock die due to drowning. It can also lead to epidemics and diseases.

2.4.2 Secondary effects:

Water supplies- Contamination of water. Clean drinking water becomes scarce. Diseases- Unhygienic conditions. Spread of water-borne diseases Crops and food supplies- Shortage of food crops can be caused due to loss of

entire harvest. Trees - Non-tolerant species can die from suffocation


2.4.3 Tertiary/long-term effects:

Economic- Economic hardship, due to: temporary decline in tourism, rebuilding costs, food shortage leading to price increase etc

2.5 DROUGHT

Drought is a condition of lesser than normal availability of water, and as such it is a management issue as a technical one. A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. Although droughts can persist for several years, even a short, intense drought can cause significant damage and harm the local economy. According to the UN, an area of fertile soil the size of Ukraine (approx. 603,628 km²) is lost every year because of drought, deforestation and climate instability.

The complex interplay of climate factors (lack of enough rainfall, uneven distribution over time and space), and non-climate factors (such as land situation and water management practices) results in widespread and sometime irreversible impacts on vulnerable livelihood systems. During a drought season, low rainfall in many parts of the region and consequent depressed agricultural production and erosion of productive assets can result in malnutrition, migration and shifts in occupational patterns.

When the word ‘drought’ is used commonly, the intended definition is meteorological drought, which is brought about when there is prolonged period with less than average precipitation. However, there are generally three types of conditions that are referred to as drought. Other than meteorological drought, agricultural drought is brought about when there is insufficient moisture for average crop production and hydrological drought is brought about when the water reserves available in sources such as aquifers, lakes and reservoirs fall below the statistical average.

Generally, rainfall is related to the amount of water vapour in the atmosphere, combined with the upward forcing of the air mass containing that water vapour. If either of these is reduced, the result is a drought. In case of India, droughts are generally caused by failure of summer monsoon. Fig. 2.8 shows areas prone to drought in India. The bluish colors indicate areas that get more rain than is evaporated from the heat, while the yellow to brown shades indicate regions where evaporation is greater than precipitation. The browner the color, the drier the region.

Periods of drought can have significant environmental, agricultural, health, economic and social consequences. Some of effects include death of livestock, reduced crop yields, wildfires, dust storms, malnutrition, dehydration and related diseases, famine due to lack of water for irrigation, mass migration, war over natural resources, reduced electricity production and social unrest.


Fig. 2.8: Areas prone to drought in India

2.6 LANDSLIDE

A landslide is a geological phenomenon which includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments. Although the action of gravity is the primary driving force for a landslide to occur, there are other contributing factors affecting the original slope stability. Typically, pre-conditional factors build up specific sub-surface conditions that make the area/slope prone to failure, whereas the actual landslide often requires a trigger before being released.

Landslides are caused when the stability of a slope changes from a stable to an unstable condition. A change in the stability of a slope can be caused by a number of factors, acting together or alone:

2.6.1 Natural causes:

Groundwater pressure acting to destabilize the slope Loss or absence of vertical vegetative structure, soil nutrients, and soil structure. Erosion of the toe of a slope by rivers or ocean waves


Weakening of a slope through saturation by snowmelt, glaciers melting, or heavy rains

Earthquakes adding loads to barely-stable slopes Earthquake-caused liquefaction destabilizing slopes Volcanic eruptions

Fig. 2.9: Landslide prone areas


2.6.2 Human causes:

Vibrations from machinery or traffic Blasting Earthwork which alters the shape of a slope, or which imposes new loads on an

existing slope In shallow soils, the removal of deep-rooted vegetation that binds colluviums to

bedrock Construction, agricultural, or forestry activities which change the amount of water

which infiltrates into the soil.

Landslides may destroy human habitat, block roads, bury buildings, destroy plantations and consequently cause great economic loss. Landslides can also threaten ‘life line' services such as water, power, telecommunication and transportation network. Fig. 2.9 shows the landslide prone areas in India.

2.7 CYCLONE

Cyclone is a large scale, atmospheric wind and pressure system characterized by low pressure at its centre and by circular wind motion. Millions of people living in the coastal areas of the west Atlantic, east and south Pacific and north and south Indian Ocean, regularly face cyclones, also known as ‘hurricane’ in western hemisphere, ‘typhoon’ in western Pacific, ‘willy willy’ near Australia and ‘baguious’ in Philippines.

Every cyclone begins as tropical low-pressure depression, created by oceanic temperature rising above 260C, which rotates clockwise in the southern hemisphere and anticlockwise in the northern hemisphere, forming a gigantic and highly volatile atmospheric system, with an eye at the vortex (10-50 km) which is a relatively calm area, an eyewall (10-15 km high and 50 km long) of gale winds and intense clouds and spiral bands of convective clouds with torrential rains (a few km wide and hundreds of km long), that move above 34 knots (64km/h). The cyclones moving more than 90 km, 120 km and 225 km per hour respectively have been classified as severe, very severe and super cyclone.

More often the cyclone blows over and dissipated by its own momentum without causing much damage due to reduction of the moisture and increase in surface friction, but sometimes it landfalls on the coastal settlements with very high wind velocity, torrential rain and massive storm surges, resulting in devastating damages to life and property. The major natural disaster that affects the coastal regions of India is cyclone and as India has a coastline of about 7516 kms, it is exposed to nearly 10 percent of the world’s tropical cyclones. About 71 percent of this area is in ten states (Gujarat, Maharashtra, Goa, Karnataka, Kerala, Tamil Nadu, Puducherry, Andhra Pradesh, Orissa and West Bengal). The islands of Andaman, Nicobar and Lakshadweep are also prone to cyclones. On an average, about five or six tropical cyclones form in the Bay of Bengal and Arabian sea and hit the coast every year. Out of these, two or three are severe. Table 2.1 shows the


major cyclones of India and Bangladesh. Fig. 2.10 shows the areas prone to cyclone in India.

Table 2.1: Major Cyclones of India and Bangladesh

Sl. No. Year Name of the Country No. of Deaths Storm Surge (in feet)

1 1737 Hoogli, West Bengal (India) 3,00,000 40’

2 1876 Bakerganj (Bangladesh) 2,50,000 10’-40’

3 1885 False point (Orissa) 5,000 22’

4 1960 Bangladesh 5,490 19’

5 1961 Bangladesh 11,468 16’

6 1970 Bangladesh 2,00,000 13- 17’

7 1971 Paradeep, Orissa (India) 10,000 7’- 20’

8 1977 Chirala, Andhra Pradesh 10,000 16’-18’

9 1990 Andhra Pradesh 990 13’-17’

10 1991 Bangladesh 1,38,000 7’-20’

11 1998 Porbander cyclone 1,173 --

12 1999 Paradeep, Orissa 9,885 30’

2.8 OCEAN ATMOSPHERE

The oceans and the atmosphere are the two large reservoirs of water in the Earth's hydrologic cycle. The two systems are complexly linked to one another and are responsible for Earth's weather and climate. The oceans help to regulate temperature in the lower part of the atmosphere. The atmosphere is in large part responsible for the circulation of ocean water through waves and currents.

Earth's atmosphere consists of a mixture of Nitrogen (N2) and Oxygen (O2). At the Earth's surface, dry air is composed of about 79% N2, 20% O2, and 1% Argon (Ar). It can also contain up to 4% water vapor at saturation, but saturation depends on temperature.

Relative humidity is the term used to describe saturation of atmosphere with water vapor. When the relative humidity is 100%, the atmosphere is saturated with respect to water vapor, and precipitation results. Other gases occur in the atmosphere in small amounts. Among the most important of these other gases is Carbon Dioxide (CO2).


Fig. 2.10: Map of India showing the cyclone prone areas

2.8.1 The atmosphere

The atmosphere has a layered structure as shown in Fig. 2.11. Each layer is defined on the basis of properties such as pressure, temperature, and chemical composition. The layer closest to the surface is called the troposphere, which extends to an altitude of 10 to 15 km. Temperature decreases upward in the troposphere to the tropopause (the boundary between the troposphere and the next layer up, the stratosphere). The troposphere contains about 90% of the mass of the atmosphere, including nearly all of the water vapor. Weather is controlled mostly in the troposphere.


Fig. 2.11: Layered atmosphere structure

2.8.2 Solar Radiation and the Atmosphere

Radiation reaching the Earth from the Sun is electromagnetic radiation. Electromagnetic radiation can be divided into different regions depending on wavelength. Note that visible light is the part of the electromagnetic spectrum to which human eyes are sensitive. Earth receives all wavelengths of solar radiation. But certain gases and other contaminants in the atmosphere have different effects on different wavelengths of radiation.

2.8.3 The Carbon Cycle

In order to understand whether or not humans are having an effect on atmospheric carbon concentrations, we must look at how carbon moves through the environment. Carbon is stored in four main reservoirs.

1. In the atmosphere as CO2 gas. From here it exchanges with seawater or water in the atmosphere to return to the oceans, or exchanges with the biosphere by photosynthesis, where it is extracted from the atmosphere by plants. CO2 returns to the atmosphere by respiration from living organisms, from decay of dead organisms, from weathering of rocks, from leakage of petroleum reservoirs, and from burning of fossil fuels by humans.

2. In the hydrosphere (oceans and surface waters) as dissolved CO2. From here it precipitates to form chemical sedimentary rocks, or is taken up by organisms to enter the biosphere. CO2 returns to the hydrosphere by dissolution of carbonate minerals in rocks and


shells, by respiration of living organisms, by reaction with the atmosphere, and by input from streams and groundwater.

3. In the biosphere where it occurs as organic compounds in organisms. CO2 enters the biosphere mainly through photosynthesis. From organisms it can return to the atmosphere by respiration and by decay when organisms die, or it can become buried in the Earth.

4. In the Earth's lithosphere as carbonate minerals, graphite, coal, petroleum. From here it can return to the atmosphere by weathering, volcanic eruptions, hot springs, or by human extraction and burning to produce energy.

Cycling between the atmosphere and the biosphere occurs about every 4.5 years. Cycling between the other reservoirs probably occurs on an average of millions of years.

2.8.4 Circulation in the Atmosphere

The air in troposphere undergoes circulation because of convection. Convection is a mode of heat transfer. Convection in the atmosphere is mainly the result of the fact that more of the Sun's heat energy is received by parts of the Earth near the Equator than at the poles. Thus, air at the equator is heated reducing its density. Lower density causes the air to rise. At the top of the troposphere this air spreads toward the poles.

If the Earth were not rotating, this would result in a convection cell, with warm moist air rising at the equator, spreading toward the poles along the top of the troposphere, cooling as it moves poleward, and then descending at the poles, as shown in the Fig. 2.12. Once back at the surface of the Earth, the dry cold air would circulate back toward the equator to become warmed once again.

Areas where warm air rises and cools are centers of low atmospheric pressure. In areas where cold air descends back to the surface, pressure is higher and these are centers of high atmospheric pressure.


Fig. 2.12: Circulation of air in atmosphere

The Fig. 2.13 would only apply to a non-rotating Earth. Since the Earth is in fact rotating, atmospheric circulation patterns are much more complex. The reason for this is the Coriolis Effect. The Coriolis Effect causes any body that moves on a rotating planet to turn to the right (clockwise) in the northern hemisphere and to the left (counterclockwise) in the southern hemisphere. The effect is negligible at the equator and increases both north and south toward the poles. The Coriolis Effect occurs because the Earth rotates out from under all moving bodies like water, air, and even airplanes. Note that the Coriolis Effect depends on the initial direction of motion and not on the compass direction. If you look along the initial direction of motion the mass will be deflected toward the right in the northern hemisphere and toward the left in the southern hemisphere.

Fig. 2.13: Coriolis Effect

2.8.5 Effect of Air Circulation on Climate

Atmospheric circulation is complicated by the distribution of land and water masses on the surface of the Earth and the topography of the land. If the Earth had no oceans and a


flat land surface, the major climatic zones would all run in belts parallel to the equator. But, since the oceans are the source of moisture and the elevation of the land surface helps control where moist air will rise, climatic zones depend not only on latitude, but also on the distribution and elevation of land masses. In general, however, most of the world's desert areas occur along the mid-latitudes where dry air descends along the mid-latitude high pressure zones.

2.8.6 Hydrological cycle

The hydrological cycle, also known as the water cycle or the H2O cycle, describes the continuous movement of water on, above and below the surface of the Earth. The global water cycle can be described with physical processes which form a continuum of water movement. Hydrologic cycle was defined by the National Research Council (NRC, 1982) the as “the pathway of water as it moves in its various phases to the atmosphere, to the earth, over and through the land, to the ocean and back to the atmosphere”. A fundamental characteristic of the hydrologic cycle is that it has no beginning and it has no end. Fig. 2.14 shows the typical water cycle. It can be studied by starting at any of the following processes: Precipitation, infiltration, transpiration, evaporation, percolation, runoff and groundwater storage.

Fig. 2.14: Hydrological cycle

The hydrologic cycle begins with precipitation in the form of rain, snow, sleet, or hail falling on the surface of the earth. As precipitation falls, some of it may evaporate directly into the atmosphere from bodies of water, and a portion may be intercepted by vegetation. The remainder reaches the ground where it can enter the soil by a process called infiltration. Some of the infiltrating water remains near the soil surface and evaporates into the atmosphere. Another portion is extracted by plant roots and transported to leaves where it is lost to the atmosphere as a vapor. This process is called transpiration. Water will infiltrate into the soil as long as the potential rate of infiltration exceeds the rate of precipitation. When the precipitation rate exceeds the infiltration rate, excess water builds on the soil surface and moves by overland flow called surface runoff. If surface runoff is excessive or concentrated, erosion can occur. Still another portion of water that enters the soil can move vertically or laterally out of the plant root zone. Significant lateral movement of water through the soil is called throughflow or interflow. Downward movement of water through the soil is referred to as percolation.


Percolating water eventually makes its way to a saturated zone, where all spaces between rock and soil particles are filled with water. The water filling the spaces between soil particles and rock in the saturated zone is called groundwater.

2.8.7 Water Budget Water has one of the highest heat capacities of all known substances. This means that it takes a lot of heat to raise the temperature of water by just one degree. Water thus absorbs a tremendous amount of heat from solar radiation, and furthermore, because solar radiation can penetrate water easily, large amounts of solar energy are stored in the world's oceans. Further, energy is absorbed by water vapor as the latent heat of vaporization, which is the heat required for evaporating water or changing it from a liquid to a vapor. This latent heat of vaporization is given up to the atmosphere when water condenses to form liquid water as rain. If the rain changes to a solid in the form of snow or ice, it also releases a quantity of heat known as the latent heat of fusion. Thus, both liquid water and water vapor are important in absorbing heat from solar radiation and transporting and redistributing this heat around the planet. This heat provides the energy to drive the convection system in the atmosphere and thus drives the water cycle and is responsible for hazards such as floods, thunderstorms, tornadoes, and tropical cyclones.

2.9 TSUNAMI

A tsunami is a series of water waves generated by unusual, abrupt and large disturbances of the surface caused by earthquakes, volcanic eruptions, landslides, slumps and meteor falls. Hence, the storm and typhoon caused by meteorological phenomena and tides are not categorized as a tsunami. Over the past 200 years 90% of the tsunamis were caused by earthquakes under sea. Although the number of tsunamis induced by landslide and volcanic eruption is small, the damage is huge because of significantly large tsunami heights within a small area.

The term ‘tsunami’ is a combination of two Japanese words, ‘nami’, meaning a wave and ‘tsu’, meaning in a harbour or port. Because a tsunami is generated by an earthquake under the seas is small, it could be significantly amplified to be noticed by the people in the shallow coast, especially in a port and harbour. These waves would attack a coastal area and cause loss of life, catastrophic destruction to structures and infrastructure, and severely erode the shoreline by repeated attacks of several waves. Human suffering during this flooding is enormous as people are swept along with other debris in the tsunami-induced currents at speeds up to 60 km/h resulting in multiple injuries like broken bones, lacerations, abrasions, punctures and crushed body cavities that often lead to drowning. Since 1850, tsunami worldwide including the 2004 Indian Ocean tsunami have claimed the lives of over 3,50,000 coastal residents. Fig. 2.15 shows the damage due to tsunamis in India.

There are two types of tsunamis, namely, distant and local tsunamis. In most instances, the propagation of wave system resulting from a distantly generated tsunami can be treated in a simplified manner. Relatively short-period tsunami waves are more easily


damped by friction and breaking; therefore, only longer period front-running waves are of concern at a coastal site located at a great distance from the generating source.

Tsunami in the deep ocean may have very long waves length of hundred of kilometer and travels at about 800 km per hour, but amplitude of only about 1 km. It remains undetected by ships in the deep sea. However, when it approaches the coast its wavelength diminishes but amplitude grows enormously, and it takes very little time to reach its full height. Computer model can provide tsunami arrival, usually within minutes of the arrival time. Tsunamis have great erosion potential, stripping beaches of sand, coastal vegetation and dissipating its energy through the destruction of houses and coastal structure.

Although 99% of the tsunami deaths occur near the generating source, tsunamis can travel across entire ocean basins without losing much power. The 1960 Chilean tsunami reached the coat of Japan, 17000 km far from the source, only 23 hours after the generation, propagating over the Pacific Ocean at a depth of about 4000 m with the speed of 720 km/h.

Fig. 2.15: Damage due to tsunamis in India

2.10 MITIGATION


Mitigation is the effort to reduce loss of life and property by lessening the impact of disasters. Mitigation is taking action now before the next disaster so as to reduce human and financial consequences later (analyzing risk, reducing risk, insuring against risk). Disaster mitigation measures are those that eliminate or reduce the impacts and risks of hazards through proactive measures taken before an emergency or disaster occurs.

In order to provide general approach to disaster risk management, the importance of any infrastructure has to be known first. Table 2.2 shows the classification of infrastructures based on different sectors of the infrastructure.

Table 2.2 Taxonomy of infrastructureSector System Major componentsWater Water Supply Reservoirs, wells transmission aqueducts

pumping stations Treatment plants Terminal reservoirs/Tanks Trunk lines Distribution lines

Sanitary sewer Sanitary sewer Mains pumping stations treatment plantsTransportation Highway Major bridges, conventional bridges

Tunnels Limited access highways Local roads

Railway Bridge tunnels Tracks/roadbeds Stations/terminals Maintenance yards Signaling and control centers

Air transportation Runways and taxiways passenger terminals

Fuel and freight facilities Air traffic control system

Water transportation Ports/cargo handling equipment inland waterways

Canal and locksEmergency services

Police Stations communications facilitiesFire Stations communications facilities

Specialized water supply facilitiesHealth care Hospitals

Various disasters have different impacts on environment and are in turn exacerbated by the different factors of the environment. Table 2.3 shows the environmental impacts of various disasters.

Table 2.3 Disasters and their environmental impacts


Disaster events

Potential environmental impacts

Exacerbating environmental factors

Flood, storms, hurricanes, typhoons, cyclones

Sewage overflow, chemical releases from roads, farms and factories;

Hazardous debris – chemicals, medical and other materials as disaster debris;

Water-damaged household chemicals (paint, pesticides, solvents); unsafe water supplies

Ground and surface water contamination;

Loss of top soil due to rapid drain of runoff.

Habitat and ecosystem destruction (e.g., coral reefs and mangroves)

Deforestation and water siltation

Urbanization and land use/ land cover changes

Droughts Habitat and crop destruction Water scarcity

Urbanization and unsustainable resource consumption

Deforestation and land use/ land cover changes

Landslides Damage/deterioration of habitat ecosystems

Land use functions, including agriculture

Groundwater and surface water contamination

Deforestation

Land use/land cover changes

2.10.1 Types of disaster mitigation

Disaster mitigation measures may be structural (e.g. flood dikes) or non-structural (e.g. land use zoning). Mitigation activities should incorporate the measurement and assessment of the evolving risk environment. Activities may include the creation of comprehensive, pro-active tools that help decide where to focus funding and efforts in risk reduction. Fig. 2.16 shows the typical flood risk management cycle generally adopted to mitigate a disaster.


Fig. 2.16: Typical Flood Risk Management Cycle

Some examples of mitigation measures include:

Hazard mapping Adoption and enforcement of land use and zoning practices Implementing and enforcing building codes Flood plain mapping Reinforced tornado safe rooms Burying of electrical cables to prevent ice build-up Raising of homes in flood-prone areas Disaster mitigation public awareness programs Insurance programs

2.10.2 Mitigation of Floods

Floods can occur due to the spilling of water out of the normal course from rivers, channels or lakes, overflow of urban drainage systems, accumulation of rain, rise in groundwater in coastal areas, storm surges, tsunamis, glacial lake outbursts, levee failures or dam breaks. It is important to identify all potential sources of flooding. Understanding flood hazard and flooding requires hydrometerological analysis, hydrologic and hydraulic simulation of surface runoffs, floods and inundations and mechanism of flooding.

The extent of the impact depends on the characteristic of the flooding in the exposed area, i.e., the depth, duration of flooding and the velocities of the flows. Other factors such as the concentration and type of pollutants carried by flood waters also influence the intensity of impact. Identification of flood hazards is often carried out in conjunction with other related hazards such as mudflows, debris flows and landslides in order to produce multi-hazard maps and management programs, essentially taking the river basin as the unit of assessment.


Flood hazards can be reduced by adopting different approaches, say, by moderating the flood peaks or delaying flood peaks by retarding the surface runoff. Some of the options for reducing flood risks are shown in Table 2.4.

Table 2.4: Different flood mitigation measuresReduce hazard Reduce exposure Reduce vulnerability Retaining water where

it falls (increasing infiltration, rooftop storing)

Retention basins (natural wetlands or depressions, man-made like school playgrounds, household underground tanks)

Dams and reservoirs Diversion channel Land use management

(e.g., house building codes in urban areas, infrastructure building practices, appropriate spatial planning)

Structural measures on the river (dykes, river training work such as flood walls, raised infrastructure such as roads and railways)

Structural and non-structural measures/ actions by individual

Land use regulations

Flood emergency measures (flood warning and evacuation)

Physical: by improving the infrastructure, well-being, occupational opportunities and living environment.

Constitutional: by facilitating equal participation opportunities, education and awareness, providing adequate skills and social support system.

Motivational: by building awareness and facilitating self-organization.

Some measures that could be adopted to reduce the effect of flooding are:

(1) Sandbags to protect property: If flood water does get into the house, people can use a pump to remove this water. But this takes a lot of time, and damage can still be done. People can evacuate their houses, if there is time. They may take precious belongings, pets and essential items such as clothes, food and money. They will have to stay somewhere else during the flood. But damage is still done to the property and has to be dealt with when the owners return.

Governments can spend money to make river banks higher. Soil or concrete can be used to make the river banks higher. This is called a levee. When there is more water in the river, it should stay in the channel as the banks are higher.

(2) Raising banks before a flood: Sometimes a flood wall can be built by the river bank to protect the town from floods. If the river bursts its banks, the water should stay in front of the flood wall. The water will not reach the town as it is trapped between the river bank and the flood wall. Flood walls are usually white.

(3) Dams: Dams are also used to control floods. In times of really heavy rainfall, more holes can be opened to allow more water to flow into the river downstream. The water can be released quickly before it has a chance to build up.


Floodways are artificial river channels which can be built to divert the flow of extra water in rivers. The water then has two channels to flow through in times of heavy rainfall, meaning that the river banks shouldn't burst.

(4) Floodways: Flood barriers can be built across rivers. These are like walls and are similar to dams. They are usually built near the mouth of a river. Flood barriers protect against floods caused by high tides or strong winds. The flood gate is closed to keep the water out of the river. In times of normal water level, the gates are kept open to allow ships to pass through. The Thames Flood Barrier is an example.

2.10.3 Droughts

Water management strategies seem to be the only solution to conserve the precious resource of water and at the same time increase its effective utilization for agriculture development. Government of India provides immediate assistance in the form of financial funding through National Calamity Contingency Fund (NCCF). The following steps needs to be incorporated in our day to day life to preserve the water:

o Stoppage of exploitation of ground water below annual recharge levels. o Desalination of sea water for irrigation or consumption.o Reducing excess of surface runoff of water into rivers will be a major mechanism.

The runoff can be checked to allow seepage into the ground. This will increase ground water level and also protect rivers from silting and erosion.

o Carefully planned crop rotation can help to minimize erosion and allow farmers to plant less water-dependent crops in drier years.

o Increasing recharge of ground water through construction of rainwater harvesting structures like; check dams, reservoirs, ponds, roof-top harvesting etc.

o Former wastewater (sewage) that has been treated and purified for reuse.o Building canals or redirecting rivers as massive attempts at irrigation in drought-

prone areas.o Water use may be regulated (particularly outdoors). This may involve regulating the

use of sprinklers, hoses or buckets on outdoor plants, the washing of motor vehicles or other outdoor hard surfaces (including roofs and paths), topping up of swimming pools, and also the fitting of water conservation devices inside the home (including shower heads, taps and dual flush toilets).

o Cloud seeding - an artificial technique to induce rainfall.

2.10.4 Landslides

Landslide mitigation refers to lessening the effect of landslides by constructing various man made projects on slopes which are vulnerable to landslides. The simplest means of dealing with landslide hazards is to avoid construction on steep slopes and existing landslides; however, this is not always practical. Regulating land use and development to ensure that construction does not reduce slope stability is another approach. In cases where landslides affect existing structures or cannot be avoided, physical controls can be


used. Planting or encouraging natural growth of vegetation can also be an effective means of slope stabilization.

Soil slopes can also be stabilized by adopting following measures: Stability increases when ground water is prevented from rising in the slide mass by

directing surface water away from the landslide, Draining ground water away from the landslide to reduce the potential for a rise in

ground-water level, Covering the landslide with an impermeable membrane, and (or) Minimizing surface irrigation. Slope stability is also increased when weight or

retaining structures are placed at the toe of the landslide or when mass (weight) is removed from the head of the slope.

2.10.5 Cyclones

The first and probably most complex task of cyclone mitigation is to map the hazard, risk and vulnerabilities of cyclone at all levels, analyze and assess the levels of risk and monitor it continuously. In the face of increasing risk of cyclonic hazards, mitigation would remain the key and the most effective strategy to reduce the risks of cyclone. Every country and community has to decide its own mitigation strategy according to its own risks, resources and capabilities. The structural mitigation measures generally refer to capital investment on physical constructions of other development works, which include engineering measures and construction of hazard-resistant and protective structures and other protective infrastructure. Non-structural measures refer to awareness and education, policies, techno-legal systems and practices, training, and capacity development.

Structures like seawalls and embankments are probably the most effective and capital-intensive investment to mitigate the risks of cyclones. A seawall is constructed usually of reinforced concrete on the inland part of a coast to prevent the ingress of storm surges arising out of cyclones. Seawalls are essential to protect coastal cities and harbours, saline water embankments are recommended to protect rural settlements and to prevent saline water ingress into agricultural and horticultural land. Such embankments are usually a ridge built with earth or rock to contain the storm surges.

Bioshields like mangroves, casuarinas, salicornia, laucaena, striplex, palms, bamboo and other tree species and halophytes and other shrub species that can inhabit lower tidal zones can also be adopted to reduce the effect of cyclones. These can block or buffer wave action with their stems, which can measure up to 30 m and several metres in circumference. They trap sediment in their roots, thereby maintain a shallow slope on the seabed that absorbs the energy of tidal surges. They also break the high velocity of winds and thus protect agricultural crops besides providing shelter and grazing lands for the livestock and farms. They reduce evaporation from the soil, transpiration from the plants and moderate extreme temperatures. They also protect fertile coastal agricultural land from erosion. They even serve as carbon sinks as they help enhance carbon sequestration


which makes coastal communities eligible for carbon credit to earn additional income. Besides, they promote sustainable fisheries by releasing nutrients into the water.

Cyclone shelters constructed at appropriate places within easy access of the vulnerable communities can also provide an immediate protection from deaths and injuries due to collapse of their houses. Such shelters are usually built on pillars above the danger level of the storm surges/inundation, are spacious enough to accommodate a few hundred people of the neighbouring villages and provide provisions of drinking water, sanitation, and kitchen and so on. During the normal season, such shelters can be utilized as schools, dispensaries or other community purposes.

2.10.6 Tsunamis

Tsunamis, like most natural disasters, are beyond human control. There are, however, a number of techniques that can minimize the harmful effects of tsunamis to the physical environment (including built structures) and to individuals and communities. Accompanied by an effective warning system, thoughtful design and strong community organization can reduce harm from Tsunamis and other natural disasters.

Specific Site Planning Strategies to Reduce Tsunami Risk

1. Avoid Inundation Areas: Site Buildings or infrastructure away from hazard area or locate on a high point.2. Slow Water: Forests, ditches, slopes, or berms can slow down waves and filter out debris. The success of this method depends on correctly estimating the force of the tsunami.3. Steering: Water can be steered to strategically placed angled walls, ditches and paved roads. Theoretically, porous dikes can reduce the impact of violent waves.4. Blocking: Walls, hardened terraces, berms and parking structures can be built to block waves.

Indicator of tsunamis: Some tsunamis are generated by physical disturbances, they produce physical indicators of their presence and intensity. Knowledge of these indicators can be used to mitigate the damage to a coastal community. If a tsunami is generated by a large earthquake, then the ground-shaking associated with the earthquake is a clear indicator of tsunami potential. Earthquake waves travel 25 times faster than tsunami waves. However, at least 5% of the tsunamis are not generated by strong shaking earthquakes. These earthquakes are ‘slow’ and at-risk population may feel only a mild shaking. Another indicator of tsunami is an abrupt change in sea level. A rapid drawdown of a harbour coastline well below low-tide level is the most reliable indicator of an approaching tsunami. As the exposed sea floor is rapidly filled by the approaching wave, the tsunami produces a loud roar similar to a jet plane. If the tsunami occurs at night when the exposed seafloor cannot be seen, this roar may be the most reliable indicator that a tsunami is approaching the coastline.

Some measures when tsunami warning system is sounded,


If you are at the beach or near the ocean and you feel the earth shake, move immediately to higher ground, do not wait for a tsunami warning to be announced. Stay away from rivers and streams that lead to the ocean as you would stay away from the beach and ocean if there is a tsunami. A regional tsunami from a local earthquake could strike some areas before a tsunami warning could be announced.

Tsunamis generated in distant locations will generally give people enough time to move to higher ground. For locally-generated tsunamis, where you might feel the ground shake, you may only have a few minutes to move to higher ground.

High, multi-story, reinforced concrete hotels are located in many low-lying coastal areas. The upper floors of these hotels can provide a safe place to find refuge should there be a tsunami warning and you cannot move quickly inland to higher ground. Local Civil Defense procedures may, however, not allow this type of evacuation in your area. Homes and small buildings located in low-lying coastal areas are not designed to withstand tsunami impacts. Do not stay in these structures should there be a tsunami warning.

Offshore reefs and shallow areas may help break the force of tsunami waves, but large and dangerous wave can still be a threat to coastal residents in these areas. Staying away from all low-lying areas is the safest advice when there is a tsunami warning.

2.12 PROTECTION OF COASTAL ZONE

A coastal zone is the interface between the land and water. These zones are important because a majority of the world's population inhabit such zones. Coastal zones are continually changing because of the dynamic interaction between the oceans and the land. Waves and winds along the coast are both eroding rock and depositing sediment on a continuous basis, and rates of erosion and deposition vary considerably from day to day along such zones. The energy reaching the coast can become high during storms, and such high energies make coastal zones areas of high vulnerability to natural hazards. Thus, an understanding of the interactions of the oceans and the land is essential in understanding the hazards associated with coastal zones. Tides, currents, and waves bring energy to the coast.

Coastal zones in India assumes importance because of high productivity of its ecosystems, concentration of population, exploitation of renewable and nonrenewable natural resources, discharge of waste effluents and municipal sewage, industrialization and spurt in recreational activities. Coastal zones are continuously changing because of the dynamic interactions between the ocean and land. Erosion and accretion, inundation due to sea level rise and storm surge, shifting of shoreline caused by natural or anthropogenic forces, such as construction of artificial structure, port and harbors leads to changes in the coastal zone and its environment.


Thus, regular monitoring of coastal zone is indispensable. Moreover, preparation of a suitable coastal zone management plan as well as implementation of regulations in the coastal zone require spatial information on the coastal land use and land forms along with high tide and low tide lines, the inventory and status of coastal habitats and information on ESAs (Ecologically Sensitive Areas).

Integrated coastal zone management (ICZM) is a process dealing with planning and management of development, keeping in view the interest of all stake holders and sustainability of natural resources. Main objectives of ICZM are conservation of critical habitats, maintaining biodiversity and sustainable use of coastal resources. ICZM comprise of two components, management and administration. The coastal resources like beaches, mudflats, corals, mangroves and submerged sea grass are unique and not available anywhere other than the coast. Developmental activities along the coast pose the threats to the productivity and existence of these ecosystems/habitats. ICZM should address these coastal resources issues and socio economic implications of coastal communities while going for economic development. Thus, environmentally effective coastal zone management depends upon accurate and comprehensive scientific data on which policy decisions can be based. Remote sensing data because of its repetitive, multispectral and synoptic nature have proved to be extremely useful in providing information on various components of the coastal environment and therefore for ICZM.

The concept of integrated Coastal Zone Management, involves zoning of the coastal area in to preservation, conservation buffer, utilization and development zones. The first step towards this was to develop ecological sensitivity index for the vital coastal habitats using remote sensing data. Satellite data of two time frames are required to prepare maps for vital coastal habitats such as coral reefs and mangrove maps at 1:25000 scale. These maps pertaining to two or more time frames are used for change detection in order to assess the ecological conditions of these important habitats. Integrating this information with spatial information like water depth, turbidity, socioeconomic data, and industries etc., qualitative ecological sensitivity index are generated to classify the habitats in good, degrading and degraded condition. The next step is to identify the vulnerability index of these habitats using the ecological sensitivity index as input. Anthropogenic pressure and various other related parameters like proximity of the habitation, population, approachability, existence and development of industries, port, jetty etc are considered in deriving the vulnerability index. As an outcome of this, vital habitats are qualitatively classified into high risk, medium risk and least risk. Based on information on the risk zonations of the habitats, preservation zone, conservation zone, utilization zone and development zone are suggested for coastal zone management.

REFERENCES

1. Disaster management and sustainable development – Emerging issues and concerns by Rajesh Anand, N. C. Jana and Sudhir Singh published by Pentagon press, 2009.

2. Disaster management – Global challenges and local solutions by Rajib Shaw and R. R. Krishnamurthy published by Universities press, 2009.


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