Natural Hazards : Floods, Droughts, Cyclones, Landslides
Natural Hazards of India
A disaster is a sudden, calamitous event that seriously disrupts the functioning of a community or society and causes human, material and economic or environmental losses that exceed the community’s capacity to cope using its own resources.
Vulnerability + Hazard =Disaster
Vulnerability- it is defined as the diminished capacity of an individual or group to anticipate, copes with, resist and recover from the impact of a natural or manmade hazard.
Types of Disaster
Hazards are routinely divided into natural or manmade, although complex disasters, where there is no single root cause, are more common in developing countries. A specific disaster may spawn a secondary disaster. A classical example is Earthquake that cause Tsunami that results in coastal flooding.
Natural Hazards are naturally occurring physical phenomenon caused either by rapid or slow onset events which can be
- Geophysical– Earthquakes, landslides, tsunamis and volcanic activity
- Hydrological– Avalanches and Floods
- Climatological- extreme temperatures, drought and wildfires
- Meteorological– Cyclones and storms
- Biological- epidemics and animal plagues
Natural Disasters and Aggravating Factors
Although these hazards are natural but there are certain aggravating factors which will result in increased frequency, complexity and severity of disasters. These factors are
- Climate change
- Unplanned urbanisation
- Under development
Earthquakes are tectonic in origin; that is the moving plates are responsible for the occurrence of violent shakes. The occurrence of an earthquake in a populated area may cause numerous casualties and injuries as well as extensive damage to property.
The Earthquake Risk in India
India’s increasing population and extensive unscientific constructions mushrooming all over, including multistoried luxury apartments, huge factory buildings, gigantic malls, supermarkets as well as warehouses and masonry buildings keep – India at high risk. During the last 15 years, the country has experienced 10 major earthquakes that have resulted in over 20,000 deaths.
As per the current seismic zone map of the country, over 59 per cent of India’s land area is under threat of moderate to severe seismic hazard-; that means it is prone to shaking of MSK Intensity VII and above In fact, the entire Himalayan belt is considered prone to great earthquakes of magnitude exceeding 8.0-; and in a relatively short span of about 50 years, four such earthquakes have occurred: 1897 Shillong (M8.7); 1905 Kangra (M8.0); 1934 Bihar-Nepal (M8.3); and 1950 Assam-Tibet (M8.6). Scientific publications have warned of the likelihood of the occurrence of very severe earthquakes in the Himalayan region, which could adversely affect the lives of several million people in India.
In our present state of knowledge, earthquakes can neither be prevented nor predicted in terms of their magnitude, or place and time of occurrence. Therefore the most effective measures of risk reduction are pre disaster mitigation, preparedness and preventive measures.
- National Earthquake Mitigation Project – it aims at strengthening the structural and non structural earthquake mitigation efforts and reducing the vulnerability in high risk areas.
- National Building Code- a national instrument providing guidelines for regulating the building construction activities.
- Building Material & Technology promotion council
- Institutional arrangements like NDMA
- Capacity building
Floods have been recurrent phenomenon in many parts of India, causing loss of lives and public property and bringing untold misery to the people, especially those in the rural areas. There is also a larger economic impact, as they derail economic activities, thus affecting growth. Indian continent has peculiar climatic conditions since it has floods in some parts whereas drought in other parts.
Over the years, several expert Committees have studied the problems caused by floods and suggested various measures for their management to the Government. However, despite the various steps undertaken over the last five decades, the trend of increasing damage and devastation brought by floods has posed a challenge to the Government as well as to the people. The approaches to flood management presently exercised in India also need to give a re-look to have an integrated strategy for policy and management related to floods.
Brahmaputra River Region:
This region consists of the rivers Brahmaputra & Barak and their tributaries covering seven states .The catchments of these rivers receive very heavy rainfall ranging from 110 cm. to 635 cm. a year which occurs mostly during the months of May / June to September. As a result, floods in this region are severe and quite frequent.
Ganga River Region:
The river Ganga and its numerous tributaries, of which important ones are the Yamuna, the Sone, the Ghaghra, the Gandak, the Kosi and the Mahananda, constitute this river region. The flood problem is mostly confined to the areas on the northern bank of the river Ganga. The damage is caused by the northern tributaries of the Ganga by spilling over their banks and changing their courses.
North West River Region:
The main rivers in this region are the Sutlej, the Beas, the Ravi, the Chenab and the Jhelum, the tributaries of Indus, all flowing from the Himalayas. These carry quite substantial discharge during the monsoon and also large volumes of sediment. They change their courses frequently and leave behind tracts of sandy waste. Compared to the Ganga and the Brahmaputra river region, the flood problem is relatively less in this region. The major problem is that of inadequate surface drainage which causes inundation and water logging over vast areas.
Central India and Deccan Region:
The important rivers in this region are the Narmada, the Tapi , the Mahanadi, the Godavari, the Krishna and the Cauvery. These rivers have mostly well defined stable courses. They have adequate capacity within the natural banks to carry the flood discharge except in the delta area. The lower reaches of the important rivers on the East Coast have been embanked, thus largely eliminating the flood problem.
Flood management measures in India
Different measures have been adopted to reduce the flood losses and protect the flood plains. Depending upon the nature work, Flood protection and flood management measures may be broadly classified as under:
(a) Engineering / Structural Measures
The engineering measures for flood control which bring relief to the flood prone areas by reducing flood flows and thereby the flood levels are –
(a) an artificially created reservoir behind a dam across a river
(b) a natural depression suitably improved and regulated, if necessary or
(c) by diversion of a part of the peak flow to another river or basin, where such diversion would not cause appreciable damage.
(d) by constructing a parallel channel bye passing a particular town/reach of the river prone to flooding.
The engineering methods of flood protection, which do not reduce the flood flow but reduce spilling, are:
(a) embankments which artificially raise the effective river bank and thereby prevent spilling and
(b) channel and drainage improvement works, which artificially reduce the flood water level so as to keep the same, confined within the river banks and thus prevent spilling.
The administrative methods endeavour to mitigate the flood damages by;
(a) Facilitating timely evacuation of the people and shifting of their movable property to safer grounds by having advance warning of incoming flood i.e. flood forecasting, flood warning in case of threatened inundation
(b) Discouraging creation of valuable assets/settlement of the people in the areas subject to frequent flooding i.e. enforcing flood plain zoning regulation.
the northward movement of the Indian plate towards China causes continuous stress on the rocks rendering them friable, weak and prone to landslides and earthquakes. The slow motion of the Indian crust, about 5 cm/year accumulates stress to which natural disasters are attributed. Some landslides make unique, and unparalleled catastrophes. Landslides and avalanches are among the major hydro-geological hazards that affect large parts of India besides the Himalayas, the Northeastern hill ranges, the Western Ghats, the Nilgiris, the Eastern Ghats and the Vindhyans, in that order, covering about 15 % of the landmass. The Himalayas alone count for landslides of every fame, name and description- big and small, quick and creeping, ancient and new.
The Northeastern region is badly affected by landslide problems of a bewildering variety. Landslides in the Darjeeling district of West Bengal as also those in Sikkim, Mizoram, Tripura, Meghalaya, Assam, Nagaland and Arunachal Pradesh pose chronic problems, causing recurring economic losses worth billions of rupees. A different variety of landslides, characterized by a lateritic cap, pose constant threat to the Western Ghats in the South, along the steep slopes overlooking the Konkan coast besides Nilgiris, which is highly landslide prone.
Some spectacular events of tragedies are reported as Varnavat landslide, Uttarkashi District, Malpha landslide Pithoragarh district, Okhimath landslide in Chamoli district, UK and Paglajhora in Darjeeling district as well as Sikkim, Aizawl sports complex, Mizoram.These are some of the more recent examples of landslides. The problem therefore needs to be tackled for mitigation and management for which hazard zones have to be identified and specific slides to be stabilized and managed in addition to monitoring and early warning systems to
- Use of geo textiles which reduces slope instability
- Making community aware about impact of landslides and build their capacity to reduce vulnerability
- Proper mapping of Landslide zone and shifting people from such zones
- No mining activities should be allowed in Eco sensitive zones
Cyclones are caused by atmospheric disturbances around a low-pressure area distinguished by swift and often destructive air circulation. Cyclones are usually accompanied by violent storms and bad weather. The air circulates inward in an anticlockwise direction in the Northern hemisphere and clockwise in the Southern hemisphere. Cyclones are classified as: (i) extra tropical cyclones (also called temperate cyclones); and (ii) tropical cyclones.
The Indian subcontinent is one of the worst affected regions in the world. The subcontinent with a long coastline of 8041 kilometres is exposed to nearly 10 per cent of the world’s tropical cyclones. Of these, the majority of them have their initial genesis over the Bay of Bengal and strike the East coast of India. On an average, five to six tropical cyclones form every year, of which two or three could be severe. More cyclones occur in the Bay of Bengal than the Arabian Sea and the ratio is approximately 4:1.
Tropical cyclones occur in the months of May-June and October-November. Cyclones of severe intensity and frequency in the North Indian Ocean are bi-modal in character, with their primary peak in November and secondary peak in May. The disaster potential is particularly high during landfall in the North Indian Ocean (Bay of Bengal and the Arabian Sea) due to the accompanying destructive wind, storm surges and torrential rainfall. Of these, storm surges cause the most damage as sea water inundates low lying areas of coastal regions and causes heavy floods, erodes beaches and embankments, destroys vegetation and reduces soil fertility.
- Early warning and Communication- inform those who are likely to be affected and disseminate the information by AIR, Door Darshan, local community radio etc.
- Capacity Building among people and educate people on various aspects of disaster management.
- Storm Shelters- with full amenities for both Humans and Animals
- Bio shields- vegetation, trees, shrubs which develops near the coast, they protect from strong storms and winds.
- Integrated development of coastal areas with strong infrastructure.
It is difficult to provide a precise and universally accepted definition of drought due to its varying characteristics and impacts across different regions such as rainfall patterns, human response and resilience etc. Drought is a normal, recurrent feature of climate and occurs in all climatic regimes and is usually characterized in terms of its spatial extension, intensity and duration. Drought causes economic, environmental and social impacts.
Ministry of Agriculture is the nodal Ministry in respect of monitoring and managing drought conditions and droughts are classified into meteorological droughts, hydrological droughts and agricultural droughts.
Meteorological drought is classified based on rainfall deficiency w.r.t. long term average – 25% or less is normal, 26-50% is moderate and more than 50% is severe.
Hydrological drought is best defined as deficiencies in surface and sub-surface water supplies leading to a lack of water for normal and specific needs. Such conditions arise even in times of average (or above average) precipitation when increased usage of water diminishes the reserves.
Agricultural drought is identified by 4 consecutive weeks of meteorological drought, weekly rainfall is 50 mm from 15/5/ to 15/10, 6 such consecutive weeks rest of the year and crop planted is 80% in kharif season.
In India, around 68% of the country is prone to drought in varying degrees. 35% which receives rainfall between 750 mm and 1125 mm is considered drought prone while 33% receiving less than 750 mm is chronically drought prone.
National Disaster Management Guidelines on Management of Drought
- The NDMA guidelines on management of drought are issued in 2010. The recommendations are as follows:
- Creation of Drought Monitoring Cells (DMCs) cells at state level with requisite staff.
- Preparation of vulnerability maps for each state by the State DMCs. Development of real-time drought related information by using information and communication technology.
- The watershed development approach would be taken up for drought management.
- Assessment of damage would include agricultural production, depletion of water resources, livestock population, land degradation and deforestation as well as human health.
- Revamping of Drought Management Information System of Department of Agriculture.
- To enable micro level analysis and forecasting, automatic weather station and rain-gauges to be put in place.
- Development of drought resistant crop varieties through large scale research.
- Formulation of a cloud seeding policy.
- Promoting crop diversification through sprinklers/Drip irrigation systems (micro irrigation techniques) etc.
Highly concentrated rainfall over a small area lasting for a few minutes to few hours is called a cloud burst. It leads to sudden flash floods and landslides in which houses collapse and ultimately results in human casualties on a large scale.
Cloud bursts are manifestations of an intense whirling mass of fluid, on small scale, that generate strong currents, which lift the moisture laden air with sufficient rapidity to form dense towering vertical clouds which are capable of shedding water load with great strength and ferocity.
Steep hills favour the formation of these clouds. Also, water flowing down steep slopes brings debris, boulders and uprooted trees with great velocity, damaging any structure that comes in the way.
There is no satisfactory technique for anticipating a cloud burst because they occur in relatively small scale. A very fine network of radars is required to detect the likelihood of a cloud burst which could be very expensive.Cloud bursts causes landslides and flooding.
A tsunami (pronounced su-nah-me) is a wave train, or series of waves, generated in a body of water by an impulsive disturbance that vertically displaces the water column. Earthquakes, landslides, volcanic eruptions, explosions, and even the impact of cosmic bodies, such as meteorites, can generate tsunamis. Tsunamis can savagely attack coastlines, causing devastating property damage and loss of life.
The tsunami that occurred during 2004 Sumatra-Andaman earthquake of Mw 9.3 was primarily caused by vertical displacement of the seafloor, in response to slip on the inter-plate thrust fault. The earthquake and resulting tsunami in the Indian Ocean affected many countries in Southeast Asia and beyond, including Indonesia, Sri Lanka, India, Thailand, the Maldives, Somalia, Myanmar, Malaysia, Seychelles and others.
The Government of India has put in place an Early Warning System for mitigation of such oceanogenic disasters under the control of Indian National Center for Ocean Information Services (INCOIS), Hyderabad. A state-of-the-art early warning centre was established with the necessary computational and communication infrastructure that enables reception of real-time data from sensors, analysis of the data, generation and dissemination of tsunami advisories following a standard operating procedure.
The 2004 tsunami also prompted NDMA to formulate Tsunami Risk Management Guidelines to outline inter-agency roles and responsibilities, tsunami risk preparedness, mitigation and response.
The Guidelines recommends practical and effective ways for awareness generation, capacity building, education, training and research & development for better tsunami risk management. The Guidelines explore options for effective dissemination of tsunami alert and warning messages generated by INCOIS to the concerned agencies and coastal vulnerable communities exposed to tsunamis in a coordinated manner.
A Heat Wave is a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season in the North-Western parts of India. Heat Waves typically occur between March and June, and in some rare cases even extend till July. The extreme temperatures and resultant atmospheric conditions adversely affect people living in these regions as they cause physiological stress, sometimes resulting in death.
Higher daily peak temperatures and longer, more intense heat waves are becomingly increasingly frequent globally due to climate change. India too is feeling the impact of climate change in terms of increased instances of heat waves which are more intense in nature with each passing year, and have a devastating impact on human health thereby increasing the number of heat wave casualties.
Health Impacts of Heat Waves
The health impacts of Heat Waves typically involve dehydration, heat cramps, heat exhaustion and/or heat stroke. The signs and symptoms are as follows:
- Heat Cramps: Ederna (swelling) and Syncope (Fainting) generally accompanied by fever below 39*C i.e.102*F.
- Heat Exhaustion: Fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps and sweating.
- Heat Stoke: Body temperatures of 40*C i.e. 104*F or more along with delirium, seizures or coma. This is a potential fatal condition