Millions of people living in the coastal areas of the West Atlantic, East, South Pacific and North and South Indian Oceans, regularly face the hazards of cyclone, also known as hurricane in the Western Hemisphere, typhoon in the western Pacific, willy willy near Australia and baguious in the Philippines.
Every cyclone begins as tropical low – pressure depressions, created by oceanic temperature rising above 26 degrees Celsius, which rotates clockwise in the Southern Hemisphere and counter clockwise in the Northern Hemisphere, forming a gigantic and highly volatile atmosphere system with an eye at the vortex (10 to 50 Km) which is a relatively calm area, an eye wall (10 to 15 Km in height and 50 Km in length) of gale winds and intense clouds and spiral bands of convective clouds with torrential rains (a few Km wide and hundreds of Km long) – that move above 34 knots (64 Km per hour). The cyclones moving more than 90 Km, 120 Km and 225 Km per hour respectively have been classified as severe and super cyclones.
The hurricanes in the Atlantic and Northeast Pacific basins are classified in categories I to V as per Saffir-Simpson Intensity Scale.
The lessons drawn from catastrophic cyclonic areas show that in the more developed countries, causality is less but more on the economic front. Conversely in poor countries the human losses would be more but economic losses would be less simply because the unit costs of damages are assessed lower in developing countries. In middle income countries the damages to life and property would be somewhere in between.
The most complex task of mitigation is to map the hazard, risks and vulnerabilities of cyclone at all levels, analyze and assess the levels of risks and monitor it continuously. It is only on the basis of such knowledge base that a proper and effective strategy for cyclone risk mitigation and preparedness can be developed.
Atmospheric and Remote Sensing sciences have made a huge progress in the understanding of the phenomenon of cyclones. Satellite images can spot the development of low pressure zones, Doppler radars can track them down and instrumented aircrafts can reach the cyclone eye, eye walls and spiral bands to transmit data on wind velocity, pressure and moisture contents of the low pressure zones. Powerful Software tools are available to analyze the data to make fairly accurate forecasts on the intensity, direction and location of the landfall and the likely areas to be affected by winds, rain and storm surges.
The time series data on cyclones are now utilized to map and zone the areas prone to the hazards of cyclone. Such maps are now available at a regional, district and even sub district levels in most of the countries. Such maps are also available in digital formats which enable integration of various spatial data with socio-economic, housing, infrastructure and other variables that can provide a quick assessment of the risks and vulnerabilities of cyclone based on which appropriate mitigation and preparedness strategies can be developed. But actual work on such data integration has been limited to few areas only and therefore vulnerability analysis has still to be done on the basis of ground level data collection and analysis, which is largely unattended task in most of the countries.
The satellite imageries are also supplemented with data regarding topography, vegetation, hydrology, land –use, land cover, settlement pattern etc to develop numerical models of storm surge and the inundation levels based on which timely warnings can be issued and realistic evacuation plans can be drawn up to shift the people and cattle likely to be affected by the cyclone.
However, such theoretical advances on cyclone modeling have been confronted with constraints in practical applications which would require more sustained research for accurate forecasting and simpler application format that would enable transfer of the technology to the planners and emergency response managers.
The constraints are further compounded by non-availability of accurate ground level data base and the costs involved in up-scaling such models from a pilot research phase to country wide application phase. Such works are still in progress even in advanced countries and therefore developing countries may not have the benefit of such accurate modeling in the very near future although this is well within the realm of possibility.
The other solution is the importance of Community Based Participatory Risk Assessment (PRA). Many such PRA tools have been developed in coastal areas which capture the intimate knowledge and perception that a community has about its own risks and vulnerabilities. Such perceptions have been validated by scientific analysis, lending credence to the reliability, simplicity and cost effectiveness of such assessment. More importantly, it involves the communities in the entire process making it democratic, sustainable and proactive and definitely facilities bridging the gap between assessment and preparedness or knowledge and action.
Therefore the ideal tool for assessment of cyclone risks and vulnerabilities at the local level should be a combination of scientific and traditional knowledge each supplementing the other.
Thanks and Regards,
Disaster Management Specialist and Consultant