Natural Disasters Any natural event that has an adverse effect on the socio-economic condition of the people is a natural disaster. In other words, non-man-made accidents, such as an earthquake or a flood. These are naturally occurring phenomena that are considered harmful only because of the presence of man-made physical systems. An important factor in the overall understanding of natural disasters is the vulnerability of the various man-made systems, the destructive vulnerabilities of the settlement. The spread and impact of natural disasters is not the same in all countries of the world. The number of lives and resources lost due to disasters is much higher in developing countries of the world than in developed countries, because in developing countries, there is a greater destructive vulnerability than a large number of disasters. Naturally, people in developing countries have a higher risk of natural disasters than those in developed countries. The definition of a natural disaster in relation to risk is the possibility of a change in the natural environment over a certain period of time in a given area and the associated risk is loss or destruction of life, property and state activities after the disaster. Although the number of major disasters has increased since the 1970s, the number of human deaths due to disasters has dropped by about 6% each year, as well as the loss of resources. However, in spite of effective disaster management and increasing public awareness about it, natural disasters often occur. Among the factors behind the increase in the number of natural disasters are improved global news coverage, increased population, rapid urbanization, and increased natural imbalances. Natural disasters are being taken seriously in today's world and there is a concerted global effort to alleviate them.
Natural disasters can be divided into three major categories such as climatic atmospheric disasters caused by atmospheric processes (storms, cyclones, thunderstorms, tornadoes, hurricanes, droughts, etc.), exogenetic disasters caused by surface processes (erosion, erosion, erosion, erosion, erosion, erosion) Groundwater pollution), and endogenetic groundwater disasters (earthquakes and volcanoes) caused by internal processes on the Earth's surface, often overshadow one another of these different natural disasters. Natural disasters can be identified according to seven key characteristics, namely, the extent of the event, the number of events, the duration, the aerial range, the onset speed, the spatial radiation, and the time interval. The risk of atmospheric and exogenous disasters is higher in Bangladesh and the risk of underground disasters is comparatively less. Cyclones, floods, river erosion, coastal erosion, landslides, natural groundwater pollution, etc. are the major natural disasters in Bangladesh. Of the natural disasters that occur only in Bangladesh, there is no risk of eruptions. At present, the most serious natural disaster facing Bangladesh is arsenic contamination of groundwater.
The storm is a terrible disaster in the atmosphere. Strong winds, often heavy rains and thunderstorms, high tidal waves crashing into the ocean, are all images of a natural disaster called a storm. Tropical cyclones, tornadoes, thunderstorms, tropical depression are the most common types of storms in Bangladesh.
Cyclones hit the coastal areas of Bangladesh almost every year with strong winds, sometimes reaching speeds of up to 250 km / h or above, causing waves of 3-10 m above sea level. Massive loss of life, property and livestock was caused. Cyclones in the Bay of Bengal occur mainly in two seasons, April-May and October-November. This means that before and after the monsoon season, cyclones form in the South China Sea and part of it enters the Gulf. From the Bay of Bengal they acquire water droplets and dormant heat and as a result the revived cyclone hits at full strength. Following the curve, the cyclones reach the coasts of Myanmar and Bangladesh or the east coast of India. The funnel-shaped coastal region of Bangladesh is often identified as the epicenter of cyclones in the Bay of Bengal. Gulf cyclones move from the east coast of India, to Myanmar, sometimes to Sri Lanka. However, these cyclones cause the most damage when they hit Bangladesh and West Bengal, India. The reasons behind this are the vast lowlands, the high population density, and the poor construction structure of the houses. The worst affected areas are Khulna, Patuakhali, Barisal, Noakhali, and the coastal areas of Chittagong and islands off the coast such as Bhola, Hatia, Sandwip, Monpura, Kutubdia, Maheshkhali, Nijhum Island, Urirchar and New Jagge Otha..
Tornadoes occur suddenly in the pre-monsoon warm season in Bangladesh, especially in April when the temperature is at its highest. The diameter of a tornado can range from a few meters to about two kilometers. Wind speeds can reach 300-480 km / h, and updrafts at the center of tornadoes can reach 320 km / h. Tornadoes are usually accompanied by thunder, lightning, heavy rain, and the sound of elephant trunks. A tornado is a very short-lived disaster that usually lasts 10-20 minutes, and the length of the area beyond it can be as much as 10 to 15 km, although it is small in size but completely destroys the area when it hits. Tornadoes occur more in the central region of Bangladesh than in other regions. Most of the severe tornadoes were recorded in Faridpur, Rajbari, Gopalganj, Pabna, Gazipur, Tangail and Dhaka districts.
Thunderstorms with thunderstorms occur throughout Bangladesh in the pre-monsoon warm season (March-May) and in the post-monsoon (October-November) seasons, usually in the evening. The most common name of this storm in Bangladesh is Kal Baishakhi when it occurs in early summer and the post-monsoon storm is called 'Ashwin's storm'. Strong winds, thunderstorms and lightning with heavy rainfall are common features of this storm.
Kalbaishakhi is a north-westerly storm that usually blows over Bangladesh during the April-May season, locally known as 'Kalbaishakhi'. The difference between this storm and normal storm is that it always happens with thunder and lightning. Hail is commonly seen with Kalavaishakhi. From mid-March to April, the temperature in Bangladesh rises sharply compared to the following months (winter months). In mid-April, a sharp rise in daytime temperatures was recorded across the country, especially in the northwest. In the western part of Bangladesh, Kalbaishakhi occurs at a higher rate in the last afternoon because at that time the radiated heat flow from the earth's surface takes place in the atmosphere. That is why this storm occurs in the evening. In the eastern part it usually flows from the northwest to the east and southeast at the same time, usually after dusk. The average speed of Kalbaishakhi is 40-60 km per hour, but in exceptional cases the wind speed can exceed 100 km. The duration of these storms is shorter but sometimes it can be up to 1 hour.
Houses destroyed by tornado
Cyclones are accompanied by cyclones and tidal surges in the Bay of Bengal and wreak havoc on coastal areas and remote islands in Bangladesh far more than the strong winds of a cyclone. Such devastation includes destruction of houses, uprooting of trees, destruction of crops, destruction of road buildings and various physical structures, death of people and destruction of animal resources. [Rafiq Ahmed and Masud Hasan Chowdhury]
The most common Bengali word for tidal wave is 'ban'. In Bangladesh, tidal surges are observed between April-May and September-December in the Meghna estuary and other southern coastal areas. It plays a more destructive role in Chittagong, Cox's Bazar, Barisal, Noakhali, Patuakhali, Barguna and Khulna. In the Meghna estuary, the catastrophic cyclone of 1970 (November 12-13) caused tidal surges, with the storm surging at a height of 3.05-10.8 m, with wind speeds of 222 km / h. At least 300,000 people died in this most terrifying natural disaster at sea.
On 29 April 1991, another severe cyclone hit Chittagong, Cox's Bazar, Barisal, Noakhali, Patuakhali, Barguna and Khulna. At this time a tidal wave of 5-6 m high occurred, the wind speed was 240 km / hr, 150,000 people were killed, 60,000 cattle were destroyed and the total financial loss was Rs 6,000 crore. [HS Mojaddad Farooq
Flooding due to heavy rainfall or rising river water. Floods are usually caused by heavy rainfall, ice or snow melt water, or a combination of water that exceeds the carrying capacity of the river system. About one-fifth of Bangladesh is flooded every year during the monsoon season. Bangladesh's geographical location, topography, topography and topography are responsible for the occurrence of floods. Floods usually start in May and may last until November. Five of the floods that occurred in the last fifty years were widespread and devastating. These are the floods of 1955, 1964, 196, 196 and 1998.
Floods in Bangladesh can be divided into three categories: a) monsoon floods - these floods are seasonal, the river water rises slowly and floods vast areas causing extensive loss of life and property; B) Flash flood - caused by sudden mountain slope or short-term heavy rainfall or by breaking natural or man-made dams; And c) Tidal Floods: These short duration floods are usually 3 to 6 m high and block the drainage system of the land.
The reasons responsible for the occurrence of floods in Bangladesh are: 1) Generally low altitude topography over which major rivers flow. Rivers form a densely arranged drainage network consisting of their tributaries and tributaries; 2) Heavy rainfall in upstream rivers outside the country and inland; 3) melting of snow in the Himalayas and natural migration of glaciers; 4) Inundation of river bed due to siltation / Occupancy of river side / Landslide; 5) Simultaneous increase of water in major rivers and influence of one river over another; 6) human intervention in nature; 6) The back water effect of the river as a result of the reverse action of the tides and winds; 6) response to sea surface changes; 9) Geo-structural disturbances (earthquakes, river flows and changes in topography); 10) Potential greenhouse reactions etc.
River erosion Millions of people in this country are victims of river erosion every year. Field crops, fields and dwelling lands are lost through river erosion. As can be seen, about 5% of the total floodplain of Bangladesh is directly affected by river erosion. Out of 498 upazilas or thanas of the country, river erosion has occurred in 94 upazilas. In June 1993, river erosion in 16 districts of the country left more than 25,000 families homeless. During the monsoon season, arrowheads, arrowheads, and arrowhead changes are very common. The sudden change in the behavior and aggression of the rivers not only harms the floodplain dwellers of the villages, but also harms the growing towns and infrastructure in the urban areas.
The Ganges, the Jamuna, the Padma and the Lower Meghna are the major rivers in Bangladesh. The annual rate of erosion along the right and left banks of the Ganges is 56 m and 20 m respectively. Between 1973 and 2000, the rate of rise of the Jamuna was 126 m / year. During this time the average width of the Jamuna increased from 9.7 to 11.2 km. From 1974-92, the left bank suffered the most erosion, with this massive river erosion just upstream from Aricha.
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