Chapter 7. Natural Hazards and Disasters: Causes, Consequences and Management

What is a Disaster?
• Disasters are harmful changes in nature that are disliked and feared by humankind. These are considered bad and have haunted human beings for a long time.
• Disasters are undesirable occurrences resulting from forces that are largely out of human control.

Two Types of Disasters
• Natural Disasters – Earthquakes, Tsunami, Cyclones.
• Human-Caused Disasters – Industrial accidents, Environmental pollution, acts of terrorism.

Earthquakes
• Earthquakes are most unpredictable and highly destructive of all-natural disasters.
(1) Tectonic origin: More scale of damage and area of influence is large.
(2) Volcanic origin: Less scale of damage and limited area of influence.
• As we know Indian plate is moving at a speed of one cm/year towards North and is being constantly obstructed by Eurasian plate in North.
• Resulting in accumulation of energy at different points in time.
• Building up of stress results in sudden release of energy and causes Earthquakes along with Himalayan Arch.

In Central-Western Parts of India
• It was a mystery to experience Earthquakes in one of most stable parts of land [Peninsular Block].
• It is because of presence of a Fault-Line and energy build-up along fault-line near river Krishna.

Mitigation
• Establishing Earthquake monitoring centres [seismological centres]. G.P.S. can be used to monitor movement of tectonic plates.
• Educating people on how to react during an earthquake [especially in areas which are more prone to earthquakes].

Tsunami
• Tectonic movement of volcanic activities at seafloor results in Tsunami.
• A tsunami is sudden displacement of oceanic water in form of high vertical waves. [Harbour waves or seismic waves]

Speed of Wave and Depth of Sea Water
• More shallow seawater more speed of wave. More deep-sea water less speed of wave.
• Therefore, Coasts are more affected by Tsunamis rather than mid oceans. It is because deep water has a very long wavelength and limited wave height. As opposed to this in shallow water wavelength is reduced and wave height increases.
• After reaching land Tsunami waves release enormous energy stored in them. Then flows onto land destroying port cities and towns and other settlements.

Mitigation
• This is not very possible to mitigate damage through Tsunami.
• India joined International Tsunami Warning System after December 2004 Tsunami.

Floods
• Inundation of land and human settlements by rise of water in channels.
• Floods occur when water in form of surface runoff exceeds carrying capacity of river channels.

Droughts
• Prolonged shortage of water due to:
(1) Inadequate Precipitation, (2) Excessive rate of evaporation and, (3) Over utilisation of water from reservoirs.

Four Types of Droughts
Meteorological drought: Prolonged period of Inadequate rainfall.
Hydrological drought: Results when availability of water in reservoirs falls below level that precipitation can replenish.
Agricultural drought: Low soil moisture – A region less than 30% of which area is unirrigated.
Ecological drought: Due to a shortage of water, natural ecosystem of an area fails, leading to ecological loss.

Mitigation
• Provision for distribution of safe drinking water, medicine & food for victims.
• Shifting of people and livestock to safe places. Planning for interlinking of rivers and construction of reservoirs or dams.

Drought Prone Areas in India
• Droughts and floods are two accompanying features of Indian climate. According to some estimates, nearly 19% of total geographical area of country and 12% of its total population suffer due to drought every year.
• About 30% of country’s total area is identified as drought prone.
• On basis of severity of droughts, India can be divided into following regions:
• Extreme Drought Affected Areas: Most parts of Rajasthan, particularly areas to west of Aravali hills, i.e. Marusthali and Kachchh regions of Gujarat fall in this category.
• Severe Drought Prone Area: Parts of eastern Rajasthan, most parts of Madhya Pradesh, eastern parts of Maharashtra, interior parts of Andhra Pradesh and Karnataka Plateau, northern parts of interior Tamil Nadu and southern parts of Jharkhand and interior Odisha are included in this category.
• Moderate Drought Affected Area: Northern parts of Rajasthan, Haryana, southern districts of Uttar Pradesh, remaining parts of Gujarat, Maharashtra except Konkan, Jharkhand & Coimbatore plateau of Tamil Nadu and interior Karnataka are included in this category.

Consequences of Drought
• Droughts have drastic effects on various other aspects of environment and society.
• Crop failure leading to scarcity of food grains [akal], fodder [trinkal], inadequate rainfall, resulting in shortage of water [jalkal], and often shortage in all three [trikal] is most devastating.
• Large-scale death of cattle and other animals.
• Migration of humans and livestock
• Consumption of contaminated water resulting in spread of many waterborne diseases like gastroenteritis, cholera, hepatitis.

Tropical Cyclone
• Tropical area is an intense low-pressure area between 30°N to 30°S latitudes in atmosphere around which high-velocity wind blows.
• Horizontal Extension: 500–1000 km; Vertical Extension: 12–14 km.

Conditions for Tropical Cyclones
• Large and continuous supply of warm and moist air.
• Strong Coriolis Force: prevent filling of low pressure at centre. [Absence of Coriolis force between 0° to 15° latitude].
• Unstable condition through troposphere creates local disturbances around which a cyclone develops.

Structure of Tropical Cyclones
• Eye of cyclone: Warm and low pressure at centre or cloudless core.
• Large pressure gradients: Isobars are closely placed to each other showing high-pressure gradients.

Consequences of Tropical Cyclones
• Energy to tropical cyclones comes from latent heat released by warm moist air.
• Hence, with an increase in distance from sea [the Arabian Sea and Bay of Bengal] force of cyclone decreases.
• Coastal areas are mostly affected. This results in an abnormal rise in sea level called a Storm Surge.

Landslides
• Rapid sliding of a large mass of bedrocks. Sudden, unpredictable and largely controlled by regional factors.

Zonal Classification
Very high vulnerability zone: Highly unstable, young mountainous areas in Himalayas and Andaman and Nicobar Islands.
High Vulnerability zone: Same as previous one but only difference is combination, intensities and frequency of controlling factors. All Himalayan states and N.E. states except Assam plains.
Moderate to low vulnerability zone: Areas that receive less precipitation such as Trans-Himalayan areas of Ladakh and Spiti [H.P.], rain shadow areas in Western and Eastern Ghats along with Deccan Plateau.
Other Areas: Remaining parts of India, particularly states like Rajasthan, Haryana, U.P., Bihar, & Assam [except Karbi Anglong Plateau].

Mitigation
• Restriction on construction and other developmental activities such as roads and dams.
• Limiting agriculture to valleys and areas with moderate slopes. Proper technique for agriculture.

Disaster Management
• Cyclonic disasters are more predictable than those Earthquakes, tsunamis & Volcanic Eruptions.

Conclusion
• introduction of Disaster Management Bill, 2005 & establishment of National Institute of Disaster Management are some examples of positive steps taken by Government of India.

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