American Journal of Environmental Engineering and Science 2015; 2(6): 65-76 Published online October 22, 2015 (http://www.openscienceonline.com/journal/ajees) Climate Changes over Bangladesh Delta: II. Extreme Weather Events and Their Consequences M. A. Awal Laboratory of Plant Ecology, Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, Bangladesh Email address [email protected] (M. A. Awal) To cite this article M. A. Awal. Climate Changes over Bangladesh Delta: II. Extreme Weather Events and Their Consequences. American Journal of Environmental Engineering and Science. Vol. 2, No. 6, 2015, pp. 65-76. Abstract Bangladesh is one of the worst victims of climate change as its geo-morphological settings invite some devastating weather shocks. Regular river floods affect 20 percent of the country, increasing up to 68 percent in extreme years. The Sylhet Division is more sensitive to flood followed by the Rangpur or Rajshahi division whereas Barisal and Khulna regions showed as less sensitive to flood. The tropical cyclones stroke Bangladesh coast over the centuries have been increased and a recent analysis of cyclone struck from the past 50 years shown that the event was so frequent that on an average only 1.2-year was enough for a cyclonic hit. The Barisal Division is most sensitive to cyclonic storm followed by Chittagong and Khulna divisions. Severe local storms of meso-scale phenomena such as tornado or Nor’wester locally called ‘Kalboishakhi’ have also occurred with hails, lightning and thunders in Bangladesh that cause great damages in local scale. All of those extreme weathers seriously destroy properties and agricultural activities thus life and livelihood are seriously affected. Evading policy can be adopted for saving life, agricultural enterprises and other properties from extreme weathers. Keywords Climate Shocks, Depression, Extreme Weather, Flood, Kalboishakhi, Nor’wester, Tornado, Tropical Cyclone 1. Introduction Today it is so common that climate change is occurring throughout the world due to global warming and the case is not an exception for Bangladesh too. Consequently the frequency of some extreme weathers such as flood, tropical cyclone, tornado or Nor’wester etc is predicted to be increased. It is reported that about 9.5 million people where more than 3.0 and 1.7 million respectively live with normal and extreme poverty are exposed to some common weather events in a year throughout Bangladesh (Awal, 2015). The figure would account as 3 to 5 times as many if any extreme weather hits the country. For example, more than 30 million people were affected throughout the country due to the each flood event occurred in 1988, 1998 and 2004 years (Rahman et al., 2009). Therefore, the issue is paramount important for Bangladesh. Bangladesh delta is located in between the Himalayas and the Bay of Bengal. Three major rivers‒ Padma, Meghna and Brahmaputra/Jamuna, and their tributaries or distributaries drain the most upstream water flow into the Bay. The country is a worst victim of all three major processes of climate change: melting of the glaciers in the Himalaya, sea level rise in the Indian Ocean, and tropical cyclones and associated storms formed in the Bay of Bengal. Eighty percent of the land is floodplains and topographically two-third of the country is less than 5 meters above sea level. This leaves a major part of the country prone to flooding. Bangladesh has experienced severe floods every 4 to 5 years that may cover more than 60 percent of the country, resulting in significant losses of properties (Reliefweb, 2009). Nevertheless, the floodplains with increasing rainfall are identified as regions more exposed to flood especially in monsoon season in Bangladesh. To form, cyclones need sea surface temperatures of 26.5 o C or greater, abundant moisture and light wind in the upper atmosphere (Neely, 2013). Global warming increases the temperature of ocean that would increase the frequency of formation of tropical cyclones. The Bay of Bengal is the best breeding ground forming tropical cyclone (Ali, 1996). It is observed that most cyclones that formed in the Bay hit Bangladesh coast regularly. It is mentioned from IPCC’s Fourth Assessment Report (IPCC, 2007) that annual mean rainfall exhibits increasing trends in Bangladesh, and
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American Journal of Environmental Engineering and Science 2015; 2(6): 65-76 Published online October 22, 2015 (http://www.openscienceonline.com/journal/ajees)
Climate Changes over Bangladesh Delta: II. Extreme Weather Events and Their Consequences
M. A. Awal
Laboratory of Plant Ecology, Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, Bangladesh
Area.jpg; accessed on July 31, 2015. Reprinted with permission.
Fig. 1. Year-wise flooded area of Bangladesh from 1954 to 2010.
Approximately 18 percent areas of Bangladesh are occupied by river, lake or
other water bodies and therefore these areas are not included in the given
flood area. Data source: http://www.ffwc.gov.bd; accessed on April 11, 2012.
Every year flood causes serious river bank erosion (Map
2). From a survey, Bangladesh Water Development Board
(BWDB) estimated that about 1,200 km river bank is eroded
and another 500 km is under threat to collapse (CCC, 2011b).
From 1982 to 1992 about 106,300 ha river banks have been
eroded due to flooding whereas only 19,300 ha land is
accreted (CDMP, 2008).
American Journal of Environmental Engineering and Science 2015; 2(6): 65-76 67
URL: http://en.banglapedia.org/index.php?title=File:NaturalHazardRiverErosionProneArea.jpg; accessed on July 31, 2015. Reprinted with permission.
Map 2. River bank erosion prone areas of Bangladesh. Source: Banglapedia.
ii) Flood frequency
Flood frequency was calculated as the total number of
flood hit divided by the total number of year passed, and the
data are shown in Map 3. The flood hit frequency was found
much higher in the Sylhet, Kurigram, Sirajganj, Rangpur,
Gaibandha, Pabna, Faridpur and Chittagong districts. The
Sylhet Division is more sensitive to flood hit followed by the
Rangpur or Rajshahi division whereas Barisal and Khulna
showed as less sensitive divisions to flood.
Map 3. Flood frequency maps at district (left) and division (right) levels since 1966. The number of flood hit at district level is weighted and brought to the
respective divisions.
68 M. A. Awal: Climate Changes over Bangladesh Delta: II. Extreme Weather Events and Their Consequences
iii) Severity of flood hit in Bangladesh
The flood events of 1955, 1974, 1988, 1998 and 2004 are
evident as most catastrophic when about 33, 36, 61, 68 and
38 percent areas of the country were inundated (Fig. 1;
http://www.thebangladesh.net/en/flood-maps-m.html; site
accessed on July 23, 2015) which resulted large scale
destruction of infrastructure and economy, and loss of lives.
The 2004, 2007 and 2008 floods are considered as
devastating floods occurred recently. Although the area
covered of 2004 flood was less than that at 1988 or 1998, but
long time exposure/prevalence, caused serious damage of the
country in 2004. Again cumulative damages due to recurring
floods occurred in 2002 and 2003 are also responsible for
great damages in 2004-flood (CCC, 2011b).
3.2. Tropical Cyclone
i) Overview of tropical cyclone in Bangladesh
The Bay of Bengal is considered as an important breeding
place of the world forming tropical cyclone (Map 4). The
Bangladesh coast is located in between the Indian coast and
Myanmar’s Peninsula that formed on top of a cone/funnel
shaped sea-land structure which invites most of the tropical
storms. Map 5 shows the track and intensity of some
devastating storms that struck Bangladesh coast. Entire
coastal region including exposed coast (adjacent to the Bay)
and interior coast are experienced to cyclonic hit (Map 6).
However, exposed coast is more vulnerable as most cyclone
landfalls to that area. Cyclonic hit create tidal flood or storm
surge about 15-20 ft height in the locality.
Map 4. Composite of cyclone tracks crossing the North Indian Ocean and the Bay of Bengal from 1970 to 2005. Source: Wikimedia Commons. URL:
https://commons.wikimedia.org/wiki/File:North_Indian_cyclone_tracks.jpg; accessed on July 31, 2015.
(a) BHOLA Cyclone, struck on Nov 12, 1970 (b) Cyclone GORKI, struck on April 29, 1991
American Journal of Environmental Engineering and Science 2015; 2(6): 65-76 69
(c) Cyclone SIDR, struck on November 15, 2007 (d) Cyclone AILA, struck on May 25, 2009
(e) Cyclone MAHASEN (Viyaru), struck on May 13, 2013 (f) Cyclone KOMEN, struck on July 31, 2015
Map 5. Map plotting the track and intensity of some devastating storms. Source: Wikimedia Commons.
URL: http://en.banglapedia.org/index.php?title=File:NaturalHazardCycloneAffectedArea.jpg; accessed on July 31, 2015. Reprinted with permission.
Map 6. General cyclone map of Bangladesh. Source: Banglapedia.
70 M. A. Awal: Climate Changes over Bangladesh Delta: II. Extreme Weather Events and Their Consequences
ii) Frequency of cyclone hit
Map 7 shows some important cyclones that tracking over
Bangladesh during the twentieth Century. The cyclones that
landfalled on the Bangladesh coast since 1795 have shown in
Fig. 2. It is evident that the cyclonic hit is being
exponentially increaed over the centuries. Cyclone in the Bay
of Bengal is to be formed more frequently due to increasing
temperature, and there is evidence that the peak intensity of
cyclone may increase by 5 to 10 percent (IPCC, 2001). The
IPCC (2007) also predicted in the 4th Assessment Report that
frequency of monsoon depressions and cyclone formation in
the Bay of Bengal has increased. The frequency of global
cyclonic hit has also increased (Haque et al., 2011). A closer
view of data of cyclone struck over the last half a century has
been analyzed and found that the landfall was so frequent
that only 1.2 year is required for a cyclonic hit (Fig. 3).
However, the intensity of cyclonic hit is declining except
during 1990–2000. The cyclone frequencies in district and
division levels are shown in Map 8. The Barisal Division is
most sensitive to cyclonic storm followed by Chittagong and
Khulna divisions. The Dhaka and Sylhet divisions are less
sensitive to cyclone whereas the Rajshahi and Rangur
divisions are free from tropical sea cyclone.
Map 7. Cyclones track over Bangladesh delta during the twentieth Century. Source: Banglapedia. Reprinted with permission.
American Journal of Environmental Engineering and Science 2015; 2(6): 65-76 71
Fig. 2. Number of occurrences of major cyclones struck since 1795 in Bangladesh. The number of cyclone hit for each 50-year period is shown above the
cyclinder bar. Source: Daily Star (a leading daily newspaper of Bangladesh) on June 1, 2009; URL: http://archive.thedailystar.net/newDesign/news-
details.php?nid=90678.
Fig. 3. Number of cyclonic hit in Bangladesh coast over last 50 years from 1961, and average time required for a cyclone. Source: BMD.
Map 8. Cyclone frequency maps at district (left) and division level (right). The number of cyclonic hit at district level is weighted and
brought to the respective divisions.
72 M. A. Awal: Climate Changes over Bangladesh Delta: II. Extreme Weather Events and Their Consequences
iii) Temporal distribution of cyclone hit in Bangladesh
The temporal distribution of all cyclones struck over
1961–2010 and 1991–2010 periods clearly shows that
tropical cyclone mostly hits within the two time boundaries:
pre-monsoon and post monsoon times (Fig. 4a–b). The
cyclone frequency was also found largely higher during post
monsoon period than the frequency found at pre-monsoon
time. The most cyclones at pre-monsoon period occurred
throughout May especially from middle to end of the month.
But the duration of post monsoon cyclonic hit was extended
quite a larger time period from mid October to mid
November. Peak cyclone frequency was recorded during 1–
15 November that corresponded well with the peak casualty
of human lives about 70% (Fig. 4c). However, the temporal
death toll at pre-monsoon period occurred quite earlier (16–
30 April) as compared to the peak frequency of hit. It is
noted that the starting time of pre-monsoon and post
monsoon cyclone events largely corresponding to the
harvesting time of Boro rice and Aman rice crops,
respectively. It would provide a best policy option for
advancing these two crop’s maturity time through early
planting or adoption of short duration rice varieties (Khan
and Awal, 2009). Thus, safe harvest of these two major crops
prior to commence the cyclone hit would be ensured.
Fig. 4. Temporal distribution of cyclonic hit (a, b) and death toll of human life (c) from cyclone attack in Bangladesh.
iv) Formation, severity and damage occurred from
cyclonic storm
Storms originate over warm tropical oceans that are
characterized by low atmospheric pressure, high winds, and
heavy rain. Structurally, tropical cyclones are typically
between 100 and 4,000 km in diameter. A developing
cyclone attracts water vapour not only from warm oceanic
atmosphere but also from surrounding terrestrial atmosphere
as it circulates over a wider area. Thus dry and transparent
atmosphere over the adjacent land is generally noticed during
the time of a cyclone formation. Drawing energy from the sea
surface and maintaining its strength as long as it remains over
warm water, a tropical cyclone generates winds that exceed
from 119 to 240 km per hour. Highest wind sustains
maximum 1–3 minutes (Table 1). As the storm system rotates
faster and faster, an eye forms in the centre (Image 1). The
eye of a storm is a roughly circular area, typically 30–65 km
in diameter. The eye is a region of mostly calm weather. But
the eye is surrounded by the eyewall, a ring of towering
thunderstorms where the most severe weather occurs. The
American Journal of Environmental Engineering and Science 2015; 2(6): 65-76 73
lowest barometric pressure occurs in the eye and can be as
much as 15% lower than the pressure outside the storm
(https://en.wikipedia.org/wiki/Eye_(cyclone); site accessed
on August 27, 2015). In case of strong storms, the eye is
characterized by light winds and clear skies, surrounded on
all sides by a towering, symmetric eyewall (Image 1a–d). In
weaker cyclones, the eye is less well defined and can be
covered by the central dense overcast, an area of high, thick
clouds that show up brightly on satellite imagery (Image 1e–
f). Weaker or disorganized storms may also feature an
eyewall that does not completely encircle the eye or have an
eye that features heavy rain. As rotating, storm acquires
greater momentum before its landfall. Shallow water that
coincides at the coast is the ideal place for landfall of a
at institutional and operational level that reduced the vast
casualty (Paul, 2009). Although less death of human (191 in
Bangladesh) is reported from cyclone AILA (on May 25,
2009) but livelihood is much affected due to heavy intrusion
of saline water inside the embankment from Bay of Bengal.
Agricultural activities and source of drinking water are
heavily disrupted due to extreme salinity and consequently
local people are still affected due to AILA.
74 M. A. Awal: Climate Changes over Bangladesh Delta: II. Extreme Weather Events and Their Consequences
Fig. 5. Maximum wind speed (a) with surge height (b) due to cyclone hit since 1960 in Bangladesh. Source: BMD.
In addition to human casualty or fatality, a great number of
people were also missed and affetced due to devastating
cyclonic hits. Cyclone caused great loss in the different
sectors like agriculture e.g. growing crops especially semi-
matured rice; infrastructures like building, mill/industry,
house, roads, bridge etc.; and basic services like
communication/telehone networks, electric power networks,
water supply networks, medical services etc in the coastal
districts (Awal et al., 2013). Communication system is
seriuosly collapsed through the disruption of road, bridge,
culverts, embankment etc. Tourism industries are also
affetced by cyclone and storm due to tidal surge/erosion and
scarcity of fresh water availability in the coastal zone.
Destruction of mills or industries may create sudden
unemployment situation that is a great concern to livelihood
security in the locality. As a whole the damages that occurred
due to storm are of great concern (Table 1).
Table 1. Salient features of some devastating cyclonic storms that strike Bangladesh coast.
Storm/Year Period
Highest wind
sustained (km/h)
Lowest
pressure*
mbar (hPa)
Affected areas Fatalities
Damage
occurred
(US$**) Formed Landfall Dissipated 3-minute 1-minute
BHOLA
Cyclone/1970
November
3
November
12
November
13 185 205 966
India,
Bangladesh
300,000–
500,000
86.40
million
Cyclone
GORKY/1991 April 24 April 29 April 30 240 260 918 Bangladesh
138,866–
150,000 1.70 billion
Cyclone
SIDR/2007
November
11
November
15
November
16 215 260 944
Bangladesh and
West Bengal,
India
~15,000 1.70 billion
Cyclone
AILA/2009 May 23 May 25 May 26 110 120 968
India,
Bangladesh 330
552.60
million
Cyclone
MAHASEN/20
13
May 10 May 13 May 17 85 85 990
Indonesia,
Slilanka, India,
Thailand,
Myanmar,
Bangladesh
107 At least 5.14
million
Cyclone
KOMEN/2015 July 26 July 31 August 2 75 – 986
Bangladesh,
Myanmar, East
India
493 Extensive
*Standard atmospheric pressure at sea level is 1013.25 millibars (mbar) or hectopascals (hPa) equivalent to 1 atmosphere (atm). ** US$ value of respective year. Source: Wikipedia Creative Commons.
American Journal of Environmental Engineering and Science 2015; 2(6): 65-76 75
3.3. Tornado/Nor’wester/Kalboishakhi
It happens from sudden depression on land due to the high
insolation load in the pre-monsoon season with transparent or
clear sky from March to May. That is higher sun load is
common prior to Summer Solstice that occurs on 21 June in
Northern Hemisphere. Table 2 summarized some devastating
tornadoes hit on various places of Bangladesh. It is localized
and the weather condition brings thunder, lightning, and hail
that cause heavy damages. However, the wind speed during
tornado hit is very faster than the sea cyclone. The damages
by Kalboishakhi storm are also occurred in the very small
area as compared to those occurred from tropical sea
cyclones. Strong Kalboishakhi can destroy everything on the
ground. Hail seriously damages developing fruits of mango,
litchi etc and growing or semi-matured/matured Boro rice in
Bangladesh.
Table 2. Salient features of some devastating Tornadoes/Nor’westers/Kalboishakhi occurred in Bangladesh.
10/04/1974 Faridpur 25.9–39.9 12–15 242 46 Innumerable Several millions
11/04/1974 Bogra 25.9–31.1 10–15 242 28 75 10
09/05/1976 Narayanganj 2.59 1–2 242 1 42 Several millions
01/04/1977 Faridpur 51.8 2–3 322 500 6000 12
26/04/1989 Manikganj (Saturia) 150.2 Several minutes 388–419 526 Innumerable Several millions
20/04/1990 Sirajganj 77.7 40 193 29 2000 –
07/05/1991 Gazipur – Several minutes 298 46 400 –
18/05/1991 Gouranadi 207.2 Several minutes 251 17 400 –
08/05/1995 Lowhajang – Several minutes 250 34 Several hundreds –
13/05/1996 Tangail 16 Unions of
6 Thanas 5–8 320–400 570 30,000 –
Source: Climate Division, BMD.
4. Conclusion
Due to gradual changes of global climate the frequency of
some extreme weather events especially flood and tropical
cyclone are increasing in Bangladesh. Flood is a common
climate change shock that occurs every monsoon season in
Bangladesh. The Bay of Bengal is the best breeding ground
forming sea cyclones and southern coast of Bangladesh is
highly sensitive for inviting those tropical cyclones.
Neverthless any place of the country may be affected by
localized tornadoes with thunder and hail during premonson
season. Evading policy can be adopted for saving life,
agricultural enterprises and other properties from extreme
weathers as these are mostly beyond to human control.
Acknowledgments
This paper is based on a study entitled ‘Adapting social
safety net programs to climate change shocks: issues and
options for Bangladesh’ financed under the Research Grants
Scheme (RGS) of the National Food Policy Capacity
Strengthening Programme (NFPCSP). The purpose of the
RGS was to assist in improving research and dialogue within
civil society so as to inform and enrich the implementation of
the National Food Policy. The NFPCSP is implemented by
the Food and Agriculture Organization of the United Nations
(FAO) and the Food Planning and Monitoring Unit (FPMU),
Ministry of Food with the financial support of EU and
USAID.
The author is gratefully acknowledged Professor Ahmed
A. Jamal, Managing Editor, Banglapedia, Asiatic Society of
Bangladesh to give his kind permission for using some
invaluable maps of Banglapedia that made the article useful
one.
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