Natural Hazards: Causes and Effects - Disaster Management Center ...
Natural Hazards: Causes and Effects - Disaster Management Center ... Natural Hazards: Causes and Effects - Disaster Management Center ...
Chapter 5 Tropical Cyclones Introduction Cyclones are among the most awesome events that nature can produce. They pose a major threat to lives and property in many parts of the world. Every year these sudden, unpredictable, violent storms bring widespread devastation to coastlines and islands lying in their erratic paths. A windstorm’s destructive work is done by the high wind, flood-producing rains and associated storm surges. 1 Historical Examples Tamil Nadu, India, November 1977 On November 12, 1977, a cyclone that originated in the Bay of Bengal developed winds of 90- 110 kilometers per hour (60-70 miles per hour) and struck the central coast of Tamil Nadu State in southern India. Hardest hit by the resulting floods were the areas of West Tanjore, Dindigul, Vedasandur, and Chidambaram. Of particular concern was the Vedasandur Dam area, which had recently been transformed by irrigation from an arid, sheep-raising land to a three-crop-peryear area. The floods destroyed much of the irrigation system. The number of casualties in Tamil Nadu was limited, apparently by the fact that people had heeded early warnings and moved to higher ground. On November 19, 1977, a second cyclone, which had been expected to hit Tamil Nadu, instead struck the central coast of Andhra Pradesh State in the Krishna Godavari Delta. Many people perished because advance warning was either too slowly or too narrowly disseminated. Damage in Andhra Pradesh was caused primarily by a storm surge that devastated some 65 villages, about 21 of which were completely washed away. The storm surge was reported to have been 5.7 meters (19 feet) high, 80 kilometers (50 miles) long, 16 kilometers (10 miles) wide, with a speed of 190 kilometers per hour (120 miles per hour). Many of the victims of the Andhra Pradesh cyclone were migrant laborers. This made identification of the dead difficult. The factors that combined to form this dangerous tidal wave were the low-lying flatness of the delta area, the concavity of the coastline, the gentle slope of the land into the sea, and tide heigh - at 4:30 P.M., strike time, the tide was high. Normally, as at Tamil Nadu, cyclones cause flooding upstream, which brings topsoil to lower areas. In this case, however, intrusions of sea water and downstream flooding left saline silt in low areas. Sandcasting of fields and wells not only made agricultural reclamation necessary but also made housing reconstruction difficult because saline mud would not hold together. On November 22-23, the cyclone that struck Tamil Nadu 10 days earlier crossed the southern peninsula into the Arabian Sea, gathered strength, and turned landward again. On November 23, it moved northward along the western coast, lashing northern Kerala State and the Lakshadweep Islands north of Mangalore. Damage and loss of life during this third, rejuvenated cyclone were less severe than in Tamil Nadu and Andhra Pradesh.
Altogether the combined disaster officially killed 9,796, with 4,258 missing; unofficial reports held that there were 25,800–31,000 dead, 5.462 million homeless, and millions more affected. Included in the impact was damage or destruction to over 1,400,000 houses, damage to irrigation works, roads, rail systems, public buildings and installations, and power and telecommunications networks, totaling U.S. $110,300,000. The fishing and weaving industries sustained damage valued at $22,705,881; 1,420,550 hectares (3,510,000 acres) of crops, 23,000 head of cattle and sheep, and 5,000 poultry birds were lost with an estimated value of over $353 million. 2 Dominican Republic, August and September 1979 In August and September of 1979 two of the strongest and most destructive hurricanes of the twentieth century ripped through the Caribbean, causing terrible destruction to Dominica and more still to the Dominican Republic. The summary of the damage by sector is as follows: Electric Power. The hurricanes caused extensive damage to the Dominican Republic’s electric power system. Hydroelectric power plants at Valdesia and Tavera were damaged and knocked out of operation. The transmission system from Santo Domingo southwest to Azua was almost totally destroyed, while more than 35 percent of the distribution systems in the towns of Bani and San Cristobal were down. In general, 20-70 percent of the country’s power lines were down, depending on the particular area. The financial and other resources of the Dominican Electricity Corporation were not adequate to cope with the task of reestablishing and repairing the system, especially since such materials as poles, wire, and transformers were in very short supply. Housing. Shelter needs in the wake of the storms were very high. Approximately 57,000 dwellings, housing some 350,000 people, (most of them poor) were severely damaged or destroyed. The heaviest damage was in the provinces west of Santo Domingo, often in isolated and mountainous rural locations. In one area of 160 square kilometers (100 square miles) between and to the north of Bani and San Cristobal, 75 percent of all housing was destroyed, apparently by wind. Most damage was to roofs, although in many cases doors and windows were also destroyed. The destruction of housing and other community infrastructure created serious health and refugee problems. Agriculture. The total estimated value of losses of crops and chickens from the combined effect of wind and water damage was set at U.S. $266.5 million, about 25 percent of estimated agricultural Gross Domestic Product (GDP). Most of the damage was to small farms. Physical damage to irrigation, farm and poultry industry installations, and small marine fisheries was estimated at an additional $46.4 million. As a result of storm damage, there were considerable shortages of traditional low-income food crops, mainly plantains and root crops, necessitating greatly increased food imports. Lost exports, primarily coffee, were valued at about $100 million. The combined effect of increased food imports and lost export income was to significantly worsen the Dominican Republic’s already strained balance of payments situation. Dominican forests were savaged by the storms. Approximately 94,000 trees, mostly pine and primarily in public forests and parks, were felled. The fallen trees represented a potentially valuable resource in terms of the lumber that could be recovered from them. However, damage to the forests represented a serious environmental threat in terms of potential erosion, silting, flooding, etc.
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Chapter 5<br />
Tropical Cyclones<br />
Introduction<br />
Cyclones are among the most awesome events that nature can produce. They pose a major<br />
threat to lives <strong>and</strong> property in many parts of the world. Every year these sudden, unpredictable,<br />
violent storms bring widespread devastation to coastlines <strong>and</strong> isl<strong>and</strong>s lying in their erratic paths.<br />
A windstorm’s destructive work is done by the high wind, flood-producing rains <strong>and</strong> associated<br />
storm surges. 1<br />
Historical Examples<br />
Tamil Nadu, India, November 1977<br />
On November 12, 1977, a cyclone that originated in the Bay of Bengal developed winds of 90-<br />
110 kilometers per hour (60-70 miles per hour) <strong>and</strong> struck the central coast of Tamil Nadu State<br />
in southern India. Hardest hit by the resulting floods were the areas of West Tanjore, Dindigul,<br />
Vedas<strong>and</strong>ur, <strong>and</strong> Chidambaram. Of particular concern was the Vedas<strong>and</strong>ur Dam area, which<br />
had recently been transformed by irrigation from an arid, sheep-raising l<strong>and</strong> to a three-crop-peryear<br />
area. The floods destroyed much of the irrigation system. The number of casualties in<br />
Tamil Nadu was limited, apparently by the fact that people had heeded early warnings <strong>and</strong><br />
moved to higher ground.<br />
On November 19, 1977, a second cyclone, which had been expected to hit Tamil Nadu, instead<br />
struck the central coast of Andhra Pradesh State in the Krishna Godavari Delta. Many people<br />
perished because advance warning was either too slowly or too narrowly disseminated.<br />
Damage in Andhra Pradesh was caused primarily by a storm surge that devastated some 65<br />
villages, about 21 of which were completely washed away. The storm surge was reported to<br />
have been 5.7 meters (19 feet) high, 80 kilometers (50 miles) long, 16 kilometers (10 miles)<br />
wide, with a speed of 190 kilometers per hour (120 miles per hour). Many of the victims of the<br />
Andhra Pradesh cyclone were migrant laborers. This made identification of the dead difficult.<br />
The factors that combined to form this dangerous tidal wave were the low-lying flatness of the<br />
delta area, the concavity of the coastline, the gentle slope of the l<strong>and</strong> into the sea, <strong>and</strong> tide<br />
heigh - at 4:30 P.M., strike time, the tide was high. Normally, as at Tamil Nadu, cyclones cause<br />
flooding upstream, which brings topsoil to lower areas. In this case, however, intrusions of sea<br />
water <strong>and</strong> downstream flooding left saline silt in low areas. S<strong>and</strong>casting of fields <strong>and</strong> wells not<br />
only made agricultural reclamation necessary but also made housing reconstruction difficult<br />
because saline mud would not hold together.<br />
On November 22-23, the cyclone that struck Tamil Nadu 10 days earlier crossed the southern<br />
peninsula into the Arabian Sea, gathered strength, <strong>and</strong> turned l<strong>and</strong>ward again. On November<br />
23, it moved northward along the western coast, lashing northern Kerala State <strong>and</strong> the<br />
Lakshadweep Isl<strong>and</strong>s north of Mangalore. Damage <strong>and</strong> loss of life during this third, rejuvenated<br />
cyclone were less severe than in Tamil Nadu <strong>and</strong> Andhra Pradesh.