cyclone

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cyclone

  1. 1. CYCLONES Presented byCT.Lakshmanan B.Arch., M.C.P. SRM School of Architecture SRM University
  2. 2. What is a Cyclone?a violent storm, often of vast extent,characterized by high winds rotating abouta calm center of low atmosphericpressure. This center moves onward,often with a velocity of 50km an hour. prepared by CT.Lakshmanan 2
  3. 3. What is a Cyclone? Cyclone is a region of low atmospheric pressure surrounded by high atmospheric pressure resulting in swirling atmospheric disturbance accompanied by powerful winds blowing in anticlockwise direction in the Northern Hemisphere and in the clockwise direction in the Southern Hemisphere. They occur mainly in the tropical and temperate regions of the world. prepared by CT.Lakshmanan 3
  4. 4. Cyclones are known by different names in different parts of the world Typhoons in the west Pacific Hurricanes in the Atlantic and Caribbean Tropical cyclones - Southeast and Southwest Indian Ocean. Willie-Willie in Australia Tornado in South America baguios in the Philippines cordonazos in Mexico tainos in Haiti prepared by CT.Lakshmanan 4
  5. 5. Tropical cyclones A tropical cyclone is essentially a rotating storm in the tropical oceans. It is conventionally defined as a circular storm with rotating wind speeds in excess of 64 knots (32 meters per second). The life span of a tropical cyclone is, on average, about six to nine days until it enters land or recurves into temperate latitudes, but this may vary from a few hours to as much as three to four weeks. Tropical cyclones form in the oceans between 5 to 30 degrees north and south of the equator. prepared by CT.Lakshmanan 5
  6. 6. prepared by CT.Lakshmanan 6
  7. 7. used to estimate the velocity of the wind by observing the effects of rising winds on the ocean surface and a variety of familiar objects.prepared by CT.Lakshmanan 7
  8. 8. prepared by CT.Lakshmanan 8
  9. 9. The wind zone map illustrates the area vulnerable to high wind speeds. The macro-level wind speed zones of India have been formulated and published in IS 875 (Part-3) – 1987. There are six basic wind speeds considered for zoning, namely: 55m/s (198km/hr) Very High Damage Risk Zone-A 50m/s (180 km/hr) Very High Damage Risk Zone-B 47m/s (169.2 km/hr) High Damage Risk Zone 44m/s (158.4 km/hr) Moderate Damage Risk Zone-A 39m/s (140.4 km/hr) Moderate Damage Risk Zone-B 33m/s (118.8 km/hr) Low Damage Risk Zoneprepared by CT.Lakshmanan 9
  10. 10. INDIAN CYCLONES The coastal areas are subjected to severe wind storms and cyclonic storms. A full-grown cyclone is a violent whirl in the atmosphere 150 to 1000 km across, 10 to 15 km high. Gale winds of 150 to 250 kmph or more spiral around the center of very low pressure area. Torrential rains, occasional thunder and lightning flashes - join these under an overcast black canopy. Through these churned chaotic sea and atmosphere, the cyclone moves 300 to 500 km, in a day to hit or skirt along a coast, bringing with it storm surges as high as 3 to 12 metres, as if splashing a part of the sea sometimes up to 30 km inland leaving behind death and destructions. A storm surge is the sudden abnormal rise in the sea level caused by cyclone. The sea water flows across the coast as well as inland and then recedes back to the sea. Great loss of life and property takes place in the process. prepared by CT.Lakshmanan 10
  11. 11. prepared by CT.Lakshmanan 11
  12. 12. prepared by CT.Lakshmanan 12
  13. 13. prepared by CT.Lakshmanan 13
  14. 14. Possible Risk Reduction Measures Coastalbelt plantation Hazard mapping Land use control Engineered structures Flood management Improving vegetation cover prepared by CT.Lakshmanan 14
  15. 15. Coastal belt plantationCoastal belt plantation - green belt plantation along thecoastal line in a scientific interweaving pattern canreduce the effect of the hazard.Providing a cover through green belt sustains lessdamage.Forests act as a wide buffer zone against strong windsand flash floods. Without the forest the cyclone travelfreely inland.The lack of protective forest cover allows water toinundate large areas and cause destruction.With the loss of the forest cover each consecutivecyclone can penetrate further inland. prepared by CT.Lakshmanan 15
  16. 16. Coastal belt plantation prepared by CT.Lakshmanan 16
  17. 17. Hazard mapping – Meteorological records of the wind speed andthe directions give the probability of the winds in the region.Cyclones can be predicted several days in advance. The onset isextensive and often very destructive. Past records and paths cangive the pattern of occurrence for particular wind speeds.A hazard map will illustrate the areas vulnerable to cyclone in anygiven year. It will be useful to estimate the severity of the cycloneand various damage intensities in the region. The map is preparedwith data inputs of past climatological records, history of windspeed, frequency of flooding etc. prepared by CT.Lakshmanan 17
  18. 18. Land use controlLand use control designed so that leastcritical activities are placed in vulnerableareas. Location of settlements in the floodplains is at utmost risk. Siting of keyfacilities must be marked in the land use.Policies should be in place to regulateland use and building codes should beenforced. prepared by CT.Lakshmanan 18
  19. 19. Engineered structures structures need to be built to withstand wind forces. Good site selection is also important. Majority of the buildings in coastal areas are built with locally available materials and have no engineering inputs. Good construction practice should be adopted such as: - Cyclonic wind storms inundate the coastal areas. It is advised to construct on stilts or on earth mound. - Houses can be strengthened to resist wind and flood damage. All elements holding the structures need to be properly anchored to resist the uplift or flying off of the objects. For example, avoid large overhangs of roofs, and the projections should be tied down. - A row of planted trees will act as a shield. It reduces the energy. - Buildings should be wind and water resistant. - Buildings storing food supplies must be protected against the winds and water. - Protect river embankments. - Communication lines should be installed underground. - Provide strong halls for community shelter in vulnerable locations. prepared by CT.Lakshmanan 19
  20. 20. prepared by CT.Lakshmanan 20
  21. 21. Flood managementFlood management – Torrential rains,strong wind and storm range leads toflooding in the cyclone affected areas. Thereare possibilities of landslides too. Floodmitigation measures could be incorporated(see section on floods for additionalinformation). prepared by CT.Lakshmanan 21
  22. 22. Improving vegetation cover Improving vegetation cover – The roots of the plants and trees keep the soil intact and prevent erosion and slow runoff to prevent or lessen flooding. The use of tree planted in rows will act as a windbreak. Coastal shelterbelt plantations can be developed to break severe wind speeds. It minimizes devastating effects. The Orissa calamity has also highlighted the need for urgent measures like shelterbelt plantation along cyclone-prone coastal areas. Species chosen for this purpose should not only be able to withstand the impact of strong cyclonic winds, but also check soil erosion. prepared by CT.Lakshmanan 22

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