NATURAL DISASTER MANAGEMENT
NATURAL DISASTER MANAGEMENT
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Seeing the gravity of natural disasters the need for Natural Disaster Management has been felt. The IMD monitors the rainfall situation through a network of 4,000 rain gauge stations. The rainfall monitoring gives early warning about drought. The National Remote Sensing Agency using satellite technology reports on the status of crops based on moisture vegetative index which is used in planning for drought management. A Crop Weather Watch Group meets once a week during monsoon season to assess the behaviour of rainfall, crop situation and water level in reservoirs. The Central Water Commission (CWC) has a flood forecast system- 157 flood forecasting centres-covering 62 interstate river basins. The IMD warns against cyclones through its 10 cyclone detection radars located on the coasts. The IMD’s seismological branch monitors seismic disturbances.
FLOODS
Floods are both natural and anthropogenic. Among man made causes of flood is the large scale deforestation in catchment areas of major rivers.
The Central Water Commission set up its flood forecasting station in 1959. Today it has a network of 157 forecasting stations which issue on an average nearly 5,500 flood forecasts every year. The first stage in flood forecasting is the prediction of time of incidence, intensity, duration and distribution of rainfall. Quantitative precipitation forecasting is essential.
Thanks to availability of satellites like IRS and INSATs, which can be used effectively for mapping and monitoring the flood inundated areas, flood damage assessment, flood hazard zoning and post flood river configuration and protection works. IMD in coordination with ISRO and NRSA (National Remote Sensing Agency) keeps a constant vigil on space. This has greatly improved accuracy of flood forecasts.
The Eighth Plan has emphasised on the: (i) need for extending forecasting network to other flood prone rivers ensuring close coordination of IMD, NRSA, ISRO for utilising the remote sensing techniques and telemetry; (ii) need for planning the flood management schemes within framework of an integrated long term plan in conjunction with plans for other water resource development like irrigation, power and domestic water supply.
The Central Government has set up Ganga Flood Control Commission and Brahmaputra Board which have prepared master plans for some projects in the catchment areas of the respective rivers. These plans are called Ganga Flood Control Plan and Brahmapurta Flood Control Plan.
Flash Floods: These are a highly localised phenomenon, generally caused by cloud burst at some place during monsoon, for example in early June of 1990 there were flash floods in South-West Rajasthan. Flash floods generally revitalise the dead/buried drainage systems, the ephemeral streams become very active. Considerable area cultivated unauthorisedly in the beds of the buried/ dead drainage system gets inundated. Wells also cave in with large inflow of rain water. Sheet erosion of soil takes place. These damages are in addition to the collapse of houses, roads and bridges and inundation of many low lying areas. The solution to the problem again lies in proper vegetal cover of the arid areas with suitable silvipasture systems. The embankments of the stream should be strengthened with vegetative means.
CYCLONES
Cyclones are the Tropical Revolving Storms (TRS) in the Indian Ocean regions from over the seas. They grow into violent systems, spiralling anticlockwise around a central area of low pressure. The Bay of Bengal cyclones move west or northwest and strike the east coast but some recurve and strike the Bengal, Bangladesh or Burma coast. The Arabian sea storms also move generally west or northwest across the Arabian sea towards the Arabian coast, and some of them recurve and affect the west coast of India. More storms form in the Bay of Bengal than in the Arabian sea. The frequency of formation is highest in the month of May, October and November. On an average about six cyclones form in a year, nearly half of which develop into severe storms.
DROUGHT
The effect of drought is continuous and prolonged while that of floods is devastating but instantaneous and short lived. Drought is not always continuous in any area. Sometimes it may be so for the low rainfall zones of the country.
The Department of Space and Department of Agriculture are developing the National Agricultural Drought Assessment and Management System (NADAMS) primarily based on monitoring of vegetation status through National Oceanic and Atmospheric Administration (NOAN), Satellite AVHRR (Advanced Very High Resolution Radiometer) data.
The Drought Relief Management has been greatly helped by remote sensing techniques. Early warning of drought conditions will help to undertake contingency agricultural strategies and to organise relief work where and when it is mostly needed. The LANDSAT MSS/TM and IRS data have greatly helped in targeting of potential water sites for taking up emergency well drilling programmes.
EARTHQUAKES
Earthquakes are caused whenever there is a movement or discontinuities or fractures, called faults, in the earth’s crust. There are basically three causes of earthquakes:
Movement of tectonic plates: The earth crust is not homogeneous. It is made up of large number of plates which are varying in size. These plates are not stationary, but in continuous motion which is very slow. This movement is caused by convection current within hot molten interior of the earth. Due to this movement of plates the earthquakes caused are called tectonic earthquakes.
Volcanic activities: The underground molten material (magna) builds up pressure before an eruption. This pressure causes an earthquake.
Large reservoirs and dams: The water stored in the large dams builds up pressure on the rocks under the earth’s crust. The tensile strength of the rocks is further reduced by the lubrication effect of water. This heavy pressure of water causes earthquake.
Earthquakes are measured by magnitude and intensity. The magnitude of earthquake is defined as amount of energy given off by the quake. The commonly used measuring unit is Richter scale. It is a logarithmic scale. The increase of one on the scale means a tenfold increase in the magnitude of quake. The strongest earthquake ever recorded had a magnitude of 8.9 on Richter scale.
Despite advances made in the understanding of the geological process that cause earthquakes, they still remain the most unpredictable among natural disasters. Scientists have pinpointed a few tell-tale signs that precede the onset of big quake.
These are :
Sudden stoppage of weak seismic activity along a particular fault zone stops the release of built up strain in the rocks. This may cause the earthquake. So systematic monitoring of such microquakes can provide a way of anticipating impending major quake.
Radon, a slightly radioactive substance, is found in underground water as a result of its emission from rocks. A sudden drop in the radon content of ground water after an increase of over several years, is reported to precede a major quake.
Sudden fall in the electrical resistance of rocks as a result of the seepage of water in the newly developed cracks in them may also predict a earthquake.
The first global network for monitoring and surveillance of earthquakes, known as World Wide Network of Seismic Stations (WWNSS) was set up in early sixties. Later on a few of these were converted to Seismic Research Observation Stations (SPROS). Now a modern global network called Incorporated Research Institutes of Seismicity (IRIS) has been established throughout the world.
In India IMD is the nodal agency for earthquake monitoring and related matters. It operates a national network of 36 seismic stations. However there is some inadequacy in observational network as evident from the recent Latur earthquake in Maharashtra. In order to overcome this inadequacy, a plan to upgrade and modernise national network of seismological observation equipped with sophisticated instrument has been formulated. Under this 31 stations will be provided with sophisticated instruments and fast telecommunication system. These stations are expected to cover potential seismic zones in the country. For national early warning systems, real time data acquisition from remote area is essential. For this National Satellite Telemetry Network (NSTN) has been formulated which is being executed during the Eighth Plan. Under this 5 stations will be equipped with station data processor GPS and VSAT station for fast telecommunication. The seismic data will be transmitted at a fast rate to the central hub station at New Delhi. The hub station will be provided with large dish antenna and fast computer devices. Four work stations will process the data on real time basis and disseminate it to users all over the country.
The Central Building Research Institute (CBRI) Roorkee, has developed two quake proof shelters namely Kedar Kuti and Gauri Kuti.
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