Cyclonic track analysis using GIS over the Bay of Bengal

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1 by the authors Licensee IJASER- Under Creative Commons License 3.0 Research article ISS Cyclonic track analysis using GIS over the Bay of Bengal 1 Siddiki, Ubaydur Rahaman, 2 Islam, Md. urul and 3 Ansari, Mohammad ayeem Aziz Department of Geography and Environment, Jahangirnagar University, Savar, Dhaka-1342, Bangladesh DOI: /ijaser Abstract: This paper examines the frequency, historical records, and severe cyclonic track of cyclones over the Bay of Bengal for the last 100 years. Bangladesh is located in the path of tropical cyclones originating from the Bay of Bengal. The unique combination of a large astronomical tide, a funneling coastal configuration, low flat terrain and frequent severe tropical storms occasionally produce storm surges that have killed thousands of people. This paper is an attempt to understand the behavior of this weather phenomenon; condition of formation of tropical cyclone, formation area in the Bay of Bengal, seasons of formation, landfall area, track preparation, etc. GIS method has been used to find out the formation area and tracks of Cyclones over the Bay of Bengal. The frequency of formation of depression and deep depression, Cyclonic s and Severe Cyclonic s during a particular month and year during the period of shows that most of these are formed in the Bay of Bengal during June to ovember with the highest frequency in August followed by September. It is predicted that the study will help understanding the magnitude of the problems to the concern authorities to reduce cyclonic damages in Bangladesh. Keywords: Cyclones, depression and deep depression, Cyclonic s, Severe Cyclonic s, Bay of Bengal, weather, Formation Processes, Track Preparation, Landfall Area, Frequency, GIS. 1. Introduction The coastline of Bangladesh has a funnel shape in the Bay of Bengal where the sea level is likely to rise sharply at the time of high tide and causes tidal bores when cyclones make landfall, and thousands of people living in the coastal areas are affected. Oceanographic characteristics are greatly influenced by the reversing monsoon winds and occasionally by the storm surges and cyclones. Every year tropical cyclones of the Bay of Bengal inflict heavy loss of life and property in Bangladesh coast. Global climate change resulting from anthropogenic activity is likely to manifest itself in the weather and climate of the Bay of Bengal region. The long-term trends in the frequency and intensity of tropical cyclones of the Bay of Bengal during intense cyclonic months May, October and ovember is one such problem which has been addressed in the present research. 2. Cyclone The term cyclone is derived from the Greek word 'Kyklos' meaning coil of snakes. The British-Indian scientist and meteorologist Henry Piddington coined the word 'Cyclone' to represent whirling storms expressing sufficiently the tendency to circular motion in his book The Sailor's Horn-book for the Law of s, published in A tropical cyclone is a relatively small, intensely developed low pressure cell that usually occurs over warm oceans. Its diameter can range between 200 and 2000 km. Technically a cyclone is an area of low pressure where strong winds blow around a centre in an anticlockwise direction in the orthern Hemisphere and a clockwise direction in the Southern Hemisphere. Cyclones occurring in 689 *Corresponding author ( ursgeo@juniv.edu) Received on August 19, 2012; Accepted on October 09, 2012; Published on October 28, 2012

2 the tropical regions are called tropical cyclones and those occurring elsewhere are called extra-tropical cyclones. It is characterized by a warm centre, very steep pressure gradients and strong cyclonic winds near the earth's surface. cyclones with a maximum wind speed of less than 60 km/h are called tropical depressions; when the maximum wind speed ranges between 60 and 110 km/h, they are tropical storms, and when the maximum wind speed exceeds 110 km/h, they are called tropical cyclones. (In the orth Atlantic and eastern orth Pacific regions it is called Hurricanes, in the western orth Pacific Typhoons. In meteorology, a tropical cyclone (or tropical storm, typhoon or hurricane, depending on strength and location) is a type of low-pressure system which generally forms in the tropics. cyclones are usually destructive and affect Bangladesh and its adjoining areas. Structurally, a tropical cyclone is a large, rotating area of clouds, wind, and thunderstorm activity. The primary energy source of a tropical cyclone is the release of heat of condensation from water vapour condensing at high altitudes. Because of this, a tropical cyclone can be thought of as a giant vertical heat engine. The ingredients for a tropical cyclone include a pre-existing weather disturbance, warm tropical oceans, moisture, and relatively light winds aloft. If the right conditions persist long enough, they can combine to produce the violent winds, incredible waves, torrential rains, and floods. Plate-1: Location of the Bay of Bengal 690

3 2.1 cyclogenesis cyclogenesis is the technical term describing the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occur are distinctly different from those through which mid-latitude cyclogenesis occurs. cyclogenesis involves the development of a warm-core cyclone, due to significant convection in a favorable atmospheric environment. There are six main requirements for tropical cyclogenesis: sufficiently warm sea surface temperatures, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low pressure centre, a pre-existing low level focus or disturbance, and low vertical wind shear. An average of 86 tropical cyclones of tropical storm intensity form annually worldwide, with 47 reaching hurricane/typhoon strength, and 20 becoming intense tropical cyclones (at least Category 3 intensity on the Saffir-Simpson Hurricane Scale). 2.2 Formative stages of tropical cyclone storms form only in or near pre-existing weather systems. Deepening can be a slow process requiring days for the organization of a large area with diffused winds. It can also be explosive, producing a well-formed eye within 12 hours. Winds usually remains below hurricane force in the formative stage. Strongest winds are apt to be concentrated in one quadrant, pole ward and east of the center in deepening waves in the easterlies, move variable in the equatorial trough. Surface pressure drops to about 1000 mb. Technically a cyclone is an area of low pressure where strong winds blow around a centre in an anticlockwise direction in the orthern Hemisphere and a clockwise direction in the Southern Hemisphere. Cyclones occurring in the tropical regions are called tropical cyclones and those occurring elsewhere are called extra tropical cyclones. cyclones are usually destructive and affect Bangladesh and its adjoining areas. Plate-2: Schematic representation of flow around a low-pressure area. The pressure gradient force is represented by blue arrows the Coriolis acceleration by red arrows. Palate-3: Cyclone Formation Process 691

4 Plate 4: Formative stage of a Cyclone Plate 5: Mature stage of a Cyclone. Plate 6: A mature tropical cyclone clearly displaying the main structural features. Plate 7: Eye of a Cyclone Table 1: Classification of Cyclones for SAARC Countries Country Types of disturbances Corresponding wind speed Knots Km/h Low <17 <31 Well-marked low Depression Bangladesh Deep Depression Cyclonic Severe Cyclonic SCS with Hurricane intensity Low Depression <17 <31 India Cyclonic Severe Cyclonic SCS with Hurricane intensity Pakistan Depression Deep Depression Cyclonic Severe Cyclonic SCS with Hurricane intensity Sri Lanka Low <17 <31 Depression Cyclonic Cyclone Source: WMO,

5 Beaufort scale 10-minute sustained winds (knots) Table 2: Classification of Cyclones over the world Cyclone Classifications (all winds are 10-minute averages) Indian Ocean IMD 0 6 <28 Depression Deep Depression Cyclonic Severe Cyclonic SW Indian Ocean MF Disturbance Depression Moderate Severe Australia BOM Low Cyclone (1) Cyclone (2) SW Pacific FMS Depression W Pacific JMA Depression Severe W Pacific JTWC Depression E Pacific & Atlantic HC & CPHC Depression Cyclone Cyclone (3) Hurricane (2) Cyclone Very Severe Cyclonic Intense Cyclone Very >120 Source: WMO, 1986 Super Cyclonic 2. Objectives of the Study Intense Cyclone Severe Severe Cyclone (4) Severe Cyclone (5) Typhoon Typhoon Super Typhoon Hurricane (1) Major Hurricane (3) Major Hurricane (4) Major Hurricane (5) Based on this consideration, the effect aims at examining the central theme of the present study is to understand the cyclonic track, historical records of tropical cyclones made landfall at the Bangladesh coast. The specific objectives of the study are as follows: 1. To accumulate the formation process and structure of tropical cyclones over the Bay of Bengal; 2. To plot the several severe cyclonic track over the Bay of Bengal from 1908 to 2008; and 3. To find out the seasonal variation of cyclones over the Bay of Bengal. 3. Data and Methodology The study is based on both primary and secondary data. Secondary data was used to understand the cyclone formation time, area, track of several severe cyclonic over Bay of Bengal. Besides, information related to cyclone and natural hazards were also collected from many institutions. Data processing and analysis were completed by using appropriate statistical methods. ecessary maps on cyclone and study 693

6 area and other geographic techniques were also used to reveal spatial and temporal variations in analysing perspectives on the study. In geographical studies it is highly unlikely that the necessary data will be found in only one source more often than not the relevant materials have to be pieced together from several different sources whose reliability may vary considerably with the result that the accuracy of the study may be diminished (Toyne and ewby, 1974). Efforts have been made to collect data from secondary sources. These data have been collected from Bangladesh Metrological Department (BMD), Disaster Management Bureau (DMB), and Cyclone Preparedness Programme (CPP). The unpublished documents, pictures, maps and some data have taken from internet. Arc View 3.3, Arc GIS 9.2, Win Surfer 7.0, Microsoft Excel, Geowin and also various cartographic techniques were also used to complete that research. Before accomplish conclusion different variables were checked and cross checked from time to time and other geographic techniques were also used to plot cyclonic track over the Bay of Bengal. Usual radar predictors of storm motion such as echo concentration etc are not reliable for any individual storm. Extrapolation of radar track is usually successful except in cases of recurvature. Using the existing data of 100 years ( ) pertaining to the tropical cyclone frequency and intensity in the Bay of Bengal during May, October and ovember, it is also found that the frequency of Severe Cyclonic s (SCS) over the Bay of Bengal has registered significant increasing trends in past 100 years during the intense cyclonic months. A satellite study of an unusual tropical cyclone is made to investigate its genesis, intensification, movement and the decay over sea. Frequency Distribution of Cyclone Focus in Bangladesh It is very important to analyze cyclone frequency for cyclone as well as disaster management of Bangladesh. Figure-1 and table-3 shows that most of the depression and deep depression are formed in the Bay of Bengal during May to December but it is dominating in the monsoon months with the highest frequency of them in August followed by September where y = x and R 2 = and y = x and R 2 = for monthly and decadal formation of depression and deep depression respectively. Formation rate of depression and deep depression in April is low but in the other months it is very low. The formation rate was highest between the years of 1938 to 1947 and the percentage of the frequency was over 14%. The percentage was between 10% -14% in the decade respectively , , , and The lowest value of percentage has identified 6.97% between the years Figure-1: Monthly and Decadal distribution of depression and deep depression formed in the Bay of Bengal ( ) Source: Bangladesh Meteorological Department 694

7 Table 3: Monthly and Decadal distribution of depression and deep depression formed in the Bay of Bengal ( ) Monthly Decadal Months Percentage Decade Percentage Jan Feb Mar Apr May Jun Jul Aug Sep Oct ov Total 100 Dec Total 100 Source: Bangladesh Meteorological Department Table 4: Monthly and Decadal distribution of Cyclonic s formed in the Bay of Bengal ( ) Monthly Decadal Months Percentage Decade Percentage Jan Feb Mar Apr May Jun Jul Aug Sep Oct ov Total 100 Dec Total 100 Source: Bangladesh Meteorological Department From the figure-2 and table-4, it can be seen that the formation time of cyclonic storm was highest having the frequency of more than 15% during Between the years of , , , and , it was 10-15%. The frequency of formation time of cyclone storm was below 10% between the years of , , and From the both Bar Diagram, we understood that y = 1.506x and R 2 = and y = x and R 2 = for monthly and decadal formation of cyclonic storms respectively. 695

8 Frequency %. Frequency in %. Cyclonic track analysis using GIS over the Bay of Bengal y = 1.506x R 2 = Jan Feb Mar Apr May Jun Jul Aug Sep Oct ov Dec Months Decades y = x R 2 = Figure-2: Monthly Decadal distribution and of cyclonic storms formed in the Bay of Bengal ( ) Source: Bangladesh Meteorological Department On the other hand, the severe cyclonic storms are formed in the Bay of Bengal during May, October, ovember and December and the highest frequency is in ovember. In addition, the percentage of formation time of severe cyclonic storm was lowest between the years of The highest frequency was observed between the years of The frequency of formation time of severe cyclone storm was almost alike between the years of , , , , , , and having the percentage range 6-15%. In both Bar Diagram, y = x and R 2 = and y = x and R 2 = for monthly and decadal formation of severe cyclonic storm respectively. According to figure-3 and table-5, these values indicate that there is no relationship between the Data set. From the regression line in all cases it can be said that present situation does not represent future or past. So it can be easily said that depression and deep depression, are not related to any specific month or decade whereas same statement is true for cyclonic storms and severe cyclonic storms over the Bay of Bengal. 696

9 Frequency in %. Frequency in %. Cyclonic track analysis using GIS over the Bay of Bengal 30 y = x R 2 = Jan Feb Mar Apr May Jun Jul Aug Sep Oct ov Dec Months Figure-3: Monthly and Decadal distribution of severe cyclonic storms (SCS) formed in the Bay of Bengal ( ) Decades y = x R 2 = Source: Meteorological Department Bangladesh Table 5: Monthly and Decadal distribution of Severe Cyclonic s (SCS) formed in the Bay of Bengal ( ) Monthly Decadal Months Percentage Decade Percentage Jan Feb Mar Apr May Jun Jul Aug Sep Oct ov Total 100 Dec Total Source: Bangladesh Meteorological Department 697

10 2 4 Cyclonic track analysis using GIS over the Bay of Bengal 4. Several Severe Cyclonic (SCG) plot and track over the Bay of Bengal Origination and land fall are important factors for the forecasting of tropical disturbances. In this chapter origination and Land fall of Cyclonic, Severe Cyclonic and of the Severe Cyclonic with a core of hurricane and their Land fall has been shown individually. For more clear idea and to show it on map, data are analyzed during the period of Due to this reason frequency for several Cyclone storm, SCS and SCS with a core of hurricane during over the Bay of Bengal and the Andaman Sea have been observed for making plots with them. With the help of these plots tables have been made to show the percentage of origination for the cases having landfall in Bangladesh coast and India coast. For more easily recognize, origination area has been point out into seven major regions which are: orth-west Bay of Bengal, orth-east Bay of Bengal, West-Central Bay of Bengal, East-Central Bay of Bengal, South-West Bay of Bengal, South-East Bay of Bengal, Andaman Sea. Map 1: Plot of Cyclonic and Severe Cyclonic formed in the Bay of Bengal Cyclonic Severe Cyclonic Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y BAY OF BEGAL Origination area of CS Y Y BAY OF BEGAL Origination area of SCS Source: Compiled based on the data of Bangladesh Meteorological Department The preparations of cyclone tracks for Severe Cyclonic storm with a core of Hurricane from are as follows: 698

11 Cyclonic track analysis using GIS over the Bay of Bengal 2 (06-10 December, 1981) Miles ovember, 1988) (25-29 April, 1991) (17-21 ovember, 1992) Miles (21-25 ovember, 1995) Miles Miles (15-19 May, 1997) (19-22 ovember, 1998) 11 (25-29 October, 1999) (25-29 April, 2006) Miles 9 Source: Compiled by author based on the data of Bangladesh Meteorological Department (11-15 ovember, 2007) Miles (27 April - 2 May, 2008) 9 699

12 5. Conclusion Bangladesh, due to its unique geographic shape and location, suffers from devastating tropical cyclones frequently. It is located in the path of tropical cyclones originating from the Bay of Bengal. The unique combination of a large astronomical tide, a funnelling coastal configuration, low flat terrain and frequent severe tropical storms occasionally produce storm surges that have killed thousands of people. The coastline of Bangladesh has a funnel shape in the Bay of Bengal where the sea level is likely to rise sharply at the time of high tide. Moreover, the two straight coasts located at right angles in the northern corner of the Bay of Bengal respond more effectively to multiply storm induced waves than a straight coastline. It can be seen that most of the Depression and Deep Depression are formed in the Bay of Bengal during June to ovember with the highest frequency of them in August followed by September. Their formation in April-May and December is rare but in the other months is very rare. Most of the Cyclonic formed in the Bay of Bengal during May to December with the highest frequency in ovember followed by October. Their formation in first four months is very rare with no frequency in February. Most of the Severe Cyclonic is formed in the Bay of Bengal during April, May and September-December with the highest frequency in ovember followed by May. Many depressions are formed form in the Andaman -ikobar islands of the Bay of Bengal in the pre-monsoon (generally May- June) and post-monsoon (October-ovember) periods. Some of these depressions turn into severe cyclone storms and hit the coastal regions of Bangladesh. The Bay of Bengal is an ideal breeding ground for tropical cyclones. Thus from 1891 to 2008, about 183 severe cyclones with wind speed of more than 87 kph were formed in the Bay of Bengal. References 1. Ahsan, R. M. and Eusuf, A. Z Determinants of Spatial and Gender Differences in Coastal Cyclone Shelter Use in island and Mainland Areas in Cox's Bazar Oriental Geographer, Vol. 38, os. 1 &2, January & July, Dhaka. 2. Bangladesh Bureau of Statistics Supplement o.1 to the Preliminary Report on Population Census BBS, GOB, Dhaka. 3. Banglapedia ational Encyclopaedia of Bangladesh, Dhaka: Asiatic Society of Bangladesh. 4. Burton, Ian, Robert W. Kates and Gilbert F. White The Environment as Hazard, ew York: Oxford University Press. 5. Coppock, T. J GIS and atural Hazards: An Overview from a GIS Perspective, Kluwer Academic Publishers, Dordrecht. 6. Das, S. C An Appraisal of Coastal Zone Resource Management in Bangladesh, Jahangirnagar Review, Part II: Social Science, Vols , , Jahangirnagar Univ., Pp: Das, S, C Physical Oceanography of the Bay of Bengal, Journal of BGA, Dhaka, Bangladesh. 8. ESCAP Coastal Environmental Management Plan for Bangladesh, Vol. 2, final Report, Bangkok. 9. EU Cyclone Shelter Preparatory Study (CPSP), Stage I, Feasibility Study, Draft Final Report, and Vol

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