Monitoring and forecast of disasters in bangladesh using remote sensing technology
Dr. A.M. Choudhury
Bangladesh Space Research and Remote
Sensing Organizatoin (SPARRSO),
Agargaon, Sher-e-Bangla Nagar,
Dhaka-1207.
Abstract
Bangladesh is a victim of natural disasters like floods and cyclones. About one fifth of the county is flooded every year and in a catastrophic flood like that of 1988, more than half of the country can be flooded. Again Bangladesh is afected by tropoical cyclones almost every year and some of them are very catastrophic like those of 1970 and 1991. These calmities cause huge loss of lives and property. Argents this backdrop an Advanced Meteroolgical Ground Station was established in Bangladesh with financial support from US-AID and technical in Bangladesh with financial support from US-AID and technical assistance from NASA. The station is capable of receivng data from NOAA and GMS satellites at frequent intervals. The imagery receied from these satellites are used for routine weather as well as disaste
forecasting. The paper is illustrated by flood pictures obtained for 1987 and 1988 floods and cyclones of 1970, 1985, 1988, 1991 and 1994 and 1994. In the case of cyclone, intensity estimation is made from degree of organization of the cloud using Dvorak method. Cyclone track foreacast method named TYAN developed by NASA originally for the Pacific and modified for the Bay of Bangal Cyclones has been found to indicate the area affected by the cyclone at least 24 hours in advance quite accurately.
Introduction
Bangladesh currently ranks as the world's foremost disaster-prone country. The situation is aggravated, all the more by its being the most densely populated country in the world. Environmental disasters like tropical cyclones, storm surges, floods, norwesters, tornadoes and droughts ravage the country almost every year. During the last thirty two years, the country was devastated by thirty five severe cyclones of varying intensities, the fiercest one was of 29 April 1991, when material damage was to the tune of about 2.4 billion US dollars and human casualty of about 1,40,000 lives. On a previous occasion of a similar catastrophe in 1970, about half a million lives were lost. As a comparison the hurricane Andrew, even stronger than 1991 cyclone of Bangladesh, which struck the Florida coast of USA in 1992 led to the casualty of no more than twenty human lives spread over four countries. The river Huang Ho in China which used to cause millions of deaths by flooding some hundred years back is no longer called the flood of 1988 caused economic loss to the extent of about one billion dollar2. And flooding in Bangladesh is a perennial problem. These disasters put the clock of our economic growth just backwards. Unless we can adequately deal with them, our economic progress will remain a dream onlyThe physical cause of these disasters are embodied in laws of science and hence proper scientific research is necessary to deal with them. This paper gives a brief description of monitoring and forcast of cyclones and floods in Bangladesh using remote sensing technology.
TropicaL Cyslones
The tropics can be regarded as the region of the earth lying between 30on latitude and 30 o S latitude All the tropical seas of earth with the exception of the south Atlantic and east south Pacific give birth ot deadly atmospheric phenomena known as tropical cyclones. On the average, 80 tropical cyclones are formed every year all over the globe. Bangladesh is a part of humid tropics, with the Himalayas in the north and the funnel shaped coast touching the Bay of Bengal in the south. This peculiar geography of Bangladesh causes not only the life giving monsoons but also catastrophic ravages of cyclones, norwesters, tornadoes and floods. The Bay of Bengal is an ideal breeding ground for tropical cyclones.Though solar energy ultimately controls the terrestrial weather, the following environmental conditions have been found to be prerequisites for the development of cyclone (3). (I) Absence of strong vertical wind shear of the horizontal wind near the cyclone centre and presence of strong vertical shear of opposite sign on either side of this system. The difference between the wind vectors between two vertical levels is known as the vertical wind shear (ii) Presence of low pressure region with cyclonic vorticity (iii) warm ocean temperatures. A tropical storm does not form if the sea temperature is less than 27 C. Such a high surface temperature is necessary to produce a steep lapse rate for maintaining the vertical circulation in a cyclone. This condition is met throughout the year in regions of the Bay of Bengal where cyclones are formed. A cyclone can extend upto a height of 15 kms. Some suggest that a triggering mechanism may exist in the upper atmosphere for the formation of cyclones . All the low pressure systems may not develop into cyclones. Some just die out whereas others intensity into cyclones.The Advanced Meteorological Ground Station established at SPARRSO monitors the weather through the reception of low and high resolution imagtery from US NOAA and Japanese GMS staellites at frequent intervals . These imagery are very halpful in the daily monitoring of weather and tracking of tropical cyclones. Intensity of Cyclones are estimated using Dvorak method.
Determination of the Cyclone Track:
The precise forces responsible for the motion of tropical cyclones is not understood clearly and hence determination of the path of the cyclone in advance is one of the most difficult tasks in meteorology. Recently verious statistical and numerical dynamical methods have also been introduced for the forecast of cyclone paths.St'eering Principle was 1st applied by H Mohn in 1970 (5). Untile 1950 forecasts of tropical cyclones were made by subjective methods based on synoptic maps and climatological behaviour. Following are some of the objective methods applied in modern times for cyclone forecasting. (I) Statistical methods relate predicated movement to one or more parameters in an empirical way. (ii) Dynamical techniques, on the other hand make use of some forms of the equation of motion to predict numerically the motion of cyclone from an observed initial state of the atmosphere. (iii) Hybrid model in which output parameters from a dynamical model are used in a statistical model. SPARRSO has installed a model named TYAN for predicting the track of a cyclone based on climatology of Bay of Bengal Cyclones for the last one hundred years. The model has shown promising results for the forecast of cyclone movement twenty four hour ahead of landfall (5)
