Amongst the natural hazards like earthquakes, landslides, mudslides and sometimes even the tsunami, cyclone is the one that can be timely predicted, observed, traced and warnings issued. Despite this people and live stock on the coasts perish. Millions of lives have been lost on the east coast of India and Bangladesh in the past four decades.
Is there a way out to save the masses from the nature's wrath?
First one has to understand what perils a cyclone brings. Around the world maximum people die of drowning by storm surge. It is just astonishing to note that in the cyclone of 1970 that struck Bangladesh more than 300000 people met a watery grave. Similar things happen in Australia too, but casualties were less because of lesser density of population on the vulnerable areas.
Under normal circumstances the sea water maintains its level that is the mean sea level between the low tide and the high tide level. Since times immemorial the human beings have been intelligent enough to settle at levels above the high tide. During a cyclone as it hits the land there is a sudden rise above normal water level due to strong winds and/or diminished atmospheric pressure. This creates powerful surges and water level rises beyond the high tide level. Problem of the coastal population is further compounded if the storm surge coincides with a high tide. In that eventuality the height and volume of water increase many fold and sea water can rush landwards and flood areas up to 100 kilometres. In this situation the water level rises so high that the even areas normally considered safe get deluged.
Storm tides (high tide + storm surge) combined with mighty waves create havoc on the coast, toppling buildings, uprooting trees, washing away the roads and communication and power lines or anything that comes in their wake. The path of the cyclone is always changing. It is very difficult to predict where the cyclone will hit the land. This makes the prediction of how high will be the astronomical high tide when the storm surge will strike well neigh impossible. The time difference between the high tide and the low tide is only a few hours, therefore the Meteorological office issues generalized alarms over large areas. There are times when only small pockets of population are affected by such storm tides. But one can not take chances with lives. Since one does not know where the storm will move, it is always considered safer to forewarn and move maximum population to safer areas.
The factors that influence the height and damaging qualities of a storm surge are:
James M. Shultz of Center for Disaster Epidemiology and Emergency Preparedness (DEEP Center ), Department of Epidemiology and Public Health, University of Miami School of Medicine, Miami, FL carried out research on the causes, effects and mitigation of tropical cyclones. He and his colleagues published their findings in the journal Epidemiological Reviews (2005). They have well elucidated the points. For example these scientists explain that tropical cyclone formation requires six concurrent conditions:
- An atmosphere that cools rapidly with vertical height, transforming stored heat energy from warm-ocean waters into thunderstorm activity that fuels the developing tropical system.
- Moist layers at mid-troposphere elevations (5 km) to enhance thunderstorm formation.
- Significant coriolis forces (named after Gaspard-Gustave Coriolis, a French scientist, who described it in 1835) to rotate the cyclone. As a consequence of these forces winds around the center of a cyclone rotate counterclockwise on the northern hemisphere and clockwise on the southern hemisphere.
- The presence of a near surface, organized, rotating system characterized by spin (vorticity) and low-level inflow (convergence).
- Minimal vertical wind shear-strong crosswinds at varying altitudes that can slice apart the towering vortex of cloud mass.
These conditions indicate that since the sea water can not become warm at the surface of its own, warmth is rather generated. In other words only the planet's midsection can conceive tropical storms. The centrifugal force (Coriolis force) due to earth's rotation makes the storms move towards poles. However, the temperatures of the tropics are best suited for the storms to survive; hence a tropical storm can neither be formed within 500 km of the Equator, nor in the oceans north and south of Tropics. It is an irony that more than two thirds of cyclones develop in the tropical belt above the Equator.
Geographic conditions of the east coast of our country are such that more cyclones are generated in the Bay of Bengal than in the Arabian Sea on the west. Agriculturally east coast is far richer. The Bay with land on three sides gives three times more opportunities to a cyclone to hit the land somewhere. The farmers of the east coast are the worst victims of the cyclones.
One of the worst outcomes of a cyclonic storm is the mortality. UNDP's publication, 'Reducing Disaster Risk, a challenge for development' says that tropical cyclones have caused an estimated 1.9 million deaths worldwide during past two centuries. Fortunately in the developed world cyclone attributable mortality rate has considerably lowered because of rapid response of people after a warning has been sounded, easy availability of cyclone shelters and better medical and health aid. Unfortunately in India, Bangladesh and Philippines situation is not so. Cyclone related deaths continue unabated.
There is a dire need for cyclone shelters, massive awareness programmes, mock exercises, vaccination and inoculation drives against diseases, improvement of drainage in the coastal habitats, and above all conservation of mangroves. Experiments have shown that even cashew nut plantation on the coasts acts as an effective storm barrier.
The first step in the hazard management of a recurring natural hazard like a cyclone is the preparation of a vulnerability map. Areas of high hazard, moderate hazard and low hazard have to be delineated depending upon the various parameters enumerated in the foregoing narrative. Armed with the map the district authorities have to start a massive education and awareness programme for the coastal population with the help of all types of media and schools to follow instructions in order to reduce the extent of disaster. Of course it goes without saying that an effective real time cyclone forecast and warning system has to be in place all along the coasts. Timely warning does help the threatened people to evacuate to safer places. Satellites are of great help in tracking the movements of cyclones. Before the cyclone struck Andhra Pradesh coast in 1990 the satellites had were already keeping a close watch on the movement of the cyclone and a timely warning helped evacuate 60,000 persons. The 1000 people, who could not be evacuated, perished. Compared to this in 1977 over 10,000 people died in A.P. as the state of art warning system was not in vogue then. However, despite the availability of such systems people remain blissfully ignorant and consider cyclones as their fate accompli. The myth needs to be broken completely.
The dangers of cyclones and tsunamis have to be constantly hammered in to the minds of the coastal population. Methods of preparedness to evacuate without loss if time in emergencies have to be taught and also rehearsed repeatedly. Perhaps the government as a sole agency may not able to achieve this mammoth task! The government draws more plans for the post disaster mitigation than pre-disaster. The media, educational institutions and NGOs can join hands with the government to chalk out area wise strategy to save lives, rather than to leave them at their fate.
Did our ancestors also face the vicissitudes of climates is a question that often daunts the researchers of past environments. We will read about them in the next issue.