Environment is a gift of nature. A clean environment helps in the healthy growth of biological species. But any disorder and chaos in the environment has far reaching effects over all life forms including man. These disorders may be caused by natural hazards and pollution which have attracted our attention in recent years.
Natural hazards are the outcome of the earth's natural system to balance the ecosystem. These are the part and parcel of the natural processes but attract our attention when there is increase in their frequency and intensity which may be affected by the activities of man. Earthquakes, floods, cyclones, droughts and famines and landslides etc. are some of the natural hazards in India which are of great concern to us because of their devastating roles.
An earthquake is a tremor of various intensity in the earth's surface caused by the action of the end genetic forces of the earth. It causes immense damage to life and property of the region if its intensity is measured over 7 on the Richter scale. Studies have shown that over 60% of the country's area comes under the moderate and high seismic zones. In the past a number of devastating earthquakes have been caused of which the memories of Koyna (1967), Latur (1993), and Bhuj (2001) are fresh in our mind. (For earthquakes please read para 2.6 of chapter 2 of this book).
Tsunamis-Earthquake measuring more than 7 on Richter scale in the sea bed may produce high sea waves called tsunamis. Such tsunamis caused due to the earthquake near Sumatra coast on 26th Dec. 2004 led to a loss of more than 1.5 lakh people in Indonesia, Sri Lanka and India.
In India heavy damage to life and property was caused in Andaman- Nicobar islands and Tamil Nadu coast. Severity of the tsunamis was minimised along the coasts characterised with wider continental shelves and luxuriant growth of mangrove forests. Since Andaman area lies in the high seismic zone the recurrence of tsunamis is not ruled out. The need is early warning system, planting of mangroves and building of protection walls.
The submergence of land through a temporary rise in river, lake or sea levels is called flood. It may be caused by increased rainfall, snow-melt, and high tide coinciding with a storm surge, the collapse of a dam or by movement of the land. According to Rashtriya Barh Ayog (National Commission on Floods) about 40 m. ha. Of the country's area comes under flood-prone area (cf. 25 mha in 1960s and 34 mha in 1978). Major part of this area is affected by river floods mainly spreading over the Ganga basin, the Brahmaputra basin (comprising the Barak, the Tista, the Torsa, the Subansiri, the Sankosh. the Jaldhaka, the Dibang, the Dihang and the Luhit), the north-western river basins (comprising the Jhelum, the Satluj, the Beas, the Chenab, the Ravi and the Ghaggar), the Peninsular river basins (consisting of Tapi, Narmada, Mahanadi, Baitarni. Godavari, Krishna, Pennar and Kaveri). Besides, coastal regions of Andhra Pradesh, Tamil Nadu, Orissa and Kerala are also affected by floods. The most flood prone basins are those of the Ganga (Uttar Pradesh, Bihar and West Bengal), and Brahmaputra (Assam) followed by Baitarni, the Brahmani, and the Subarnarekha basins (Orissa). These five states are the most flood prone areas of the country and Table 31.1).
Cyclones, mostly tropical cyclones/disturbances, cause immense damage to life and property of the coastal areas of Orissa, Tamil Nadu, Gujarat, Andhra Pradesh and West Bengal. These cyclones are developed in the open seas of the Bay of Bengal and the Arabian Sea and are more frequented during pre and post monsoon periods.
According to the World Meteorological Organisation, India accounts for six per cent of the total number of cyclones worldwide each year (cf. China-Japan 30 per cent and USA 23 per cent). However, India reports the maximum damages. About 20 to 25 such depressions are developed during monsoon period of which some are stronger causing damage to coastal areas. According to the IMD if the water temperature in the Bay of Bengal is more than 26°C, a normal cyclone can become ferocious.
According to the Centre for Earth Science Studies, Thiruvananthapuram east coast is the most cyclone-prone coastal region in India. The Vulnerability Atlas of India shows the Orissa coast as a high-cyclone prone area of the country. The super cyclone of October 29, 1999 with speed of nearly 300km/h left behind a trail of devastation in Orissa which had no parallel in the country in the past century. More than 11,000 people lost their lives, 1.75 million ha of the kharif crops destroyed, one- third of the State remained submerged by saline sea water and thousands of trees were uprooted.
The release of ammonia from Paradwip fertiliser plant caused panic among the people. The cyclone affected districts lost more than 90 per cent of their green cover which led to the deterioration of the coastal environment. Increased salinity caused hindrance to agricultural activities and heavy influx of
sediments badly affected the environs of the Chilka Lake (Also see pages 143-144 and figure 5.16 of this book).
4. Droughts and Famines
Drought is basically a distress situation caused by the failure of rainfall. This failure may be due to insufficient rain or due to wide gap between two or more spells of rains. Droughts are of three types..A meteorological drought is a situation when the actual rainfall is significantly less than the climatologically expected rainfall over a wide area. Here the rains do not arrive in time and are not received in adequate quantity. Such droughts are mainly concentrated in the areas falling between arid and semiarid zones of the country and are charaterised by high variability of rainfall.
There are six major causes of meteorological droughts: (a) late onset and early withdrawal of monsoons, (b) lean rainfall due to absence of depressions (low pressure system) passing over the country, (c) prolonged breaks in monsoon rainfall, (d) re-establishment of the southern branch of the jet stream, (e) upwelling of the cool water over the Arabian Sea, and (f) movement of the monsoon trough closer to the Himalayan zone.
Hydrological droughts are associated with the drying up of surface water such as rivers, streams, lakes and reservoirs (also known as surface water drought) and fall in the ground water levels (known as ground water drought). These are caused when meteorological droughts are sufficiently prolonged. Such droughts are also promoted by excessive deforestation, mining, road construction, overgrazing, and withdrawal of groundwater. All these factors have been contributing to hydrological instability and leading to drought-like situations in the region.
Agricultural droughts or soil droughts occur when soils lose their effective moisture conserving capacity so as to promote healthy crop-growth. Such droughts may exist even when meteorological droughts may not occur and vice-versa. Under extreme condition of such drought no plant would be able to survive and such condition is called desertification.
Agricultural drought is a relative category dependent on the nature of plant and soil. What could be a drought condition for paddy could well be condition of excess soil moisture for dry crops like bajra or jowar. Modern green-revolution agriculture has increased the vulnerability to such droughts in many ways such as more water demand in HYV farming, replacement of traditional drought- resistant varieties of seeds, and less use of organic fertilisers.
Disproportionate allocation of water to cash crops in the dry land areas sometimes also create agricultural drought. In Maharashtra, Karnataka and Andhra Pradesh while the staple-crops in drought affected areas are denied water cash crops like sugarcane, grapes are frequently irrigated.
Although all these three forms of drought can occur independently, the occurrence of meteorological drought is the chief reason behind hydrological and agricultural droughts. Prolonged meteorological drought will result in hydrological drought and may, thereafter, lead to agricultural drought. The transition from meteorological to hydrological drought and from that to agricultural drought is a slow process. It may take two successive meteorological droughts for hydrological drought to occur and then it slowly leads to agricultural drought.
Drought has often led to famine like conditions in the country. A bad harvest following drought leads to fall in agricultural production, scarcity of food grains, fall in the purchasing power of the people, malnutrition, starvation, death, migration, social tension, crimes and low morale of the people.
These are the main characteristics of the famines which have taken heavy toll of life in India prior to Independence. It has almost been controlled due to increased agricultural production, buffer stock of food grains, improved transport and communication facilities and several welfare measures taken by the government.
Management of Droughts
Droughts can be managed in two ways: (a) preventing the causative aspects of the droughts, (b) providing relief to victims of droughts and also rehabilitating them. Meteorological droughts can be managed by predicting the variability of changing weather. A prediction that the rainfall will be less than the normal will help the farmer to judiciously choose crops that are less water demanding. Hydro- logical droughts can be managed through biological and engineering methods involving the local peoples. Similarly the severity of the agricultural droughts could be minimised by the choice of crops.
Emphasis should be put on the drought resistant varieties of crops like sorghum, pearl millet, sunflower etc. in drought-prone areas. Tree crops have a distinct advantage over agricultural crops in moisture deficient drought areas. The impact of drought can also be mitigated by providing relief and rehabilitation.
(For distribution of drought prone areas and DPAP also see para 5.5 and figure 5.24 on pages 152-154 of this book).
Landslide is a form of mass movement in which rock and debris move rapidly down slope under the influence of gravity as a result of failure along a shear plane. The movement is often lubricated by water and tends to occur suddenly. It may result from undercutting of the slope, for example marine erosion of a sea cliff, road construction, digging of canals, mining and quarrying, overgrazing, deforestation and unscientific agricultural activities along the hill slopes. Landslides are activated by seismic tremors, heavy rainfall and deforestation. The landslide leaves a basin-shaped scar on the slope and a mass of debris at the foot, often projecting forward as a tongue.