Sea-Level Extremes and Change- Example of Bangladesh

Full text

International Conference on Mechanical, Industrial and Materials Engineering 2013 (ICMIME2013)
1-3 November, 2013, RUET, Rajshahi, Bangladesh.
Paper ID: RT-03
SEA-LEVEL EXTREMES AND CHANGE- Example of BANGLADESH
Cansu Karsili1, I. B. Muhit2, Mohammad Emdadul Hoque1, Sohidul Islam1
1Graduate student, Department of Physical Geography and Ecosystem Analysis, Lund University,
Sweden
2Department of Civil Engineering, Chittagong University of Engineering & Technology, Chittagong-
4349, Bangladesh
E-mail: imrose_cuet@live.com
Abstract
The effects of climate change are significant for worldwide. In future, climate will most likely continue to
change dramatically. During the last 100 years sea levels has already risen globally. There will be significant
impacts on several countries due to sea-level rise. However some countries such as Bangladesh which is settled
on a delta will be influenced more tragically because deltas are not suitable places to be settled on as they are
subsides each year. Bangladesh is in the top row of the list of countries which will be influenced by sea-level
rise. That is why in this study is based on Bangladesh which is the world’s biggest delta and it acquires
important agriculture land. The coast of Bangladesh, meets important food requirement of Bangladesh. If sea-
levels continue to rise in the future-which likely seems will- people who are living near the coast will be
influenced badly. Unfortunately sea-level rise will increase salinization of ground water and that will involve
water scarcity in Bangladesh. It seems the sea level rise will mostly influence humans in Bangladesh. This paper
shows the impacts of sea level rise in Bangladesh such as salinity intrusion, agriculture and ecosystems. To
prevent these impacts some precautions should be taken, some of these are Adaptation and Mitigation.
Keywords: sea-level rise, Bangladesh, vulnerability, adaptation, mitigation
1. Introduction
In the past, the main causes for climate change and sea level fluctuations were due to natural processes such as
orbital variations of earth. However, today the main reason of this problem is clearly humans. Earth is getting
hotter day by day due to different kinds of human activities which are lead to increase the global warming. And
this rising temperature leads to raise the sea level and affect the low lying part of coastal areas of the world.
Among all low lying areas, Bangladesh is the most affected by sea level rise, that’s why this area has considered
as our study area. Besides the global warming, sea level rise also depends on regional continental drifts. For
instance, some land of river deltas has subsided by several millimeters because of sediment folding. That
intensifies the existing effect of sea level rise in that region. On the other hand, some regions are remaining
unnoticed because the land is also rising in the same magnitude or more. Bangladesh is one of the most
populated countries in the world and it is settled just above the sea which is located in the mouth of three rivers:
Brahmaputra, Ganges and Meghna [1]. About 150 million people are living around these delta regions
(Houghton, 2010). Another threat for Bangladesh is impacts of cyclonic storms and monsoon. These storms
causes extreme sea level rises and floods in Bangladesh and of course affects lots of people. Sea level rise will
cause loss of one fifth of the land and many diseases will affect many peoples. Also another consequence of sea-
level rise will be the salinization of ground water and this will affect humans negatively by causing diseases.
Also there will be ecosystem lose due to the rising of sea [1]. The vulnerability of Bangladesh will be increased
due to the cyclonic storms, subsidence of delta and salinization of ground water. Due to increasing carbon
emission rate the atmosphere will continue to warm, as a result sea levels will continue to rise. Because of that
we have to find some solutions for this important problem. Adaptation and Mitigation [2] can be some of the
solutions for Bangladesh. In this study we will try to explain in what terms Bangladesh will be affected and
what can be done for least damages.
2. Aim of Study
The aim of this study is to explain reasons of extreme sea level rise, rising rate and its impacts in Bangladesh.
We want to mention some of the possible and current impacts of sea level rise in the coastal zone of Bangladesh
in order to suggest some solutions. We mention only some of these impacts such as; agriculture, salinity

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intrusion and ecosystem. But there are much more important impacts like on ground water, humans, health,
economy, settlements, fisheries, security and etc. People are vulnerable especially in the coastal zone of
Bangladesh and it is likely that in the future there can be disastrous impacts on all of these parameters. Because
of that, some possible solutions for Bangladesh within the framework of our aim is suggested. These solutions
are Adaptation and Mitigation.
3. Methodology
Our methodology is based on literature review. In order to understand the impacts of sea-level extremes it is
necessary to understand underlying causes of climate changes. The reasons of climate change and its impacts on
sea-levels tried to be explained in this study. Therefore it is important to express the meaning of vulnerability to
understand how this country will be influenced by sea-level extremes. Hereby, it is important to focus on impact
on humans to produce some solutions. Also, sea-level rise will have a dramatic impact on the agriculture land
and that will cause crucial problems for humans. We mention only some of the i mpacts in this study but it
should be considered that all of the impacts are interrelated. Further study is required to understand all these
impacts thoroughly. So, some suggestions were made for providing solutions to this problem.
4. Results
4.1 Causes of sea-level rise
Both natural processes and human activities are responsible for sea level rise. In a long time period, sea level
rise is mainly due to changes in Earth’s orbit which has a cyclic period causes changes in incoming solar
radiation. As a result of this, earth experiences glacial and interglacial periods in 400,000 years cycles. During
the glacial periods, due to the cooling of the Earth, sea levels decrease and in interglacial cycles due to warming
of earth sea levels increase [3]. This sea-level change is fundamentally associated with ice forming and melting
[4]. During the glacial cycles, cooling led to build up of ice on land, predominantly in the Northern Hemisphere,
which makes the sea levels to decrease more than 100m. However, when the atmosphere begins to warm again,
the ice caps start to melt and the ultimate result is sea level rising [5]. Fig. 1shows the sea level changes over the
past glacial-interglacial cycles and modern levels.
Fig. 1. Past and modern sea level changes; Source: Reference [6]
Since the last interglacial, there is a distinct global warming due to the warming of the Earth. However this
warming rate is accelerated since the last century (Fig. 1). The reason of this sharp warming is strictly humans.
Humans cause global warming by releasing CO2 into the atmosphere. Concentration of CO2 and other
greenhouse gases are added to the earth's atmosphere and aggregately lead to warm up the atmosphere; the
ultimate result is climate change. This rising temperature amplifies the volume of ocean water in two different
manners. Such as, it causes melt of the ice in Polar Regions and thermal expansion of the ocean water. These
two attributes are mainly accountable for increase the volume of ocean water of the earth as well as raise the sea
level. If the earth’s temperature keeps rising, the amount of ice sheet will decrease and after a certain time the
total amount of ice will disappear, which will result with extreme sea level rise [9]. If the total ice sheet in
Greenland and West Antarctic melt, sea level will increase 7m and 6m respectively [8], [9]. So, ice melting is
the most important cause of sea level rise and the following table shown that how much sea level will rise if the
ice caps on the earth's surface melt.
Another important cause of sea level rise is thermal expansion of ocean water, which is also happening because
of global warming. Between the periods of 1961-2003, ocean thermal expansion contributed about 50% of total
sea level rise [10] than estimated by the IPCC (2007). Beside ice melting and thermal expansion some other
regional factors also play a vital role for sea level changing process like as subsidence and uplifting of land and

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siltation on ocean bed [2]. Some climate models, satellite data and hydrographic observations reveal that the sea
level rise is not equal all over the world. This rise is sometimes depends on regional tectonic movement, that’s
why some region’s sea level is expected to rise slightly higher than others. For instance, because of sediment
collapse, lands in some of river delta areas subside by several millimeters. In that case, sea level rise enhances
the existing regional effects, meanwhile in some regions land is rising to the same rate or even more than sea
level itself where sea level rise remain unnoticed [1].
4.2 Current sea level rise and future projections
From 1870 to 2004, the total global mean sea level has raised 195 mm at a rate of 1.44 mm per year, for the 20th
century the sea level rise and the linear least squares trend was 160 mm and 1.7±0.3 mm per year respectively
[11]. According to IPCC, the global average sea level rate was of 1.8 (1.3 to 2.3) mm per year over the period
1961 to 2003 [2]. During 1993 to 2003, the rate is increased by 3.1 (2.4 to 3.8) mm per year (IPCC, 2007). In
1990, IPCC predicted that global sea level rise will be 9 to 88 centimeters by 2100. Later on again IPCC (2007)
estimates that in the next decade global sea level would be rise about 0.03m and end of this century it will rise
0.2 to 0.8 m, if the CO2 emissions keep continue like as it is now. Based on simple statistical model, Rahmstorf
(2007) suggested a sea level rise over the 1990 to 2100 periods by 0.5 to1.4 m. “A report prepared for the Dutch
Delta Committee, which assesses post- Fourth Assessment Report publications on the impacts of recent
warming trends on ice sheet dynamics, derives an upper bound of sea level rise of 1.1 m by 2100 [12]. In
Bangladesh the average rate of sea level rise is averagely 1.0 cm per year (Milliman et al. 1998, cited in Frihy,
2003). According to SAARC Meteorology Research Center (SAARC, cited in Alam 2003, p 15) during 1977 to
1998 periods observed that sea level at Hiron Point, Char Changa and Cox's Bazar have been rising by 4 mm, 6
mm and 7.8 mm per year respectively. The rate of sea level rise is almost half in the western coast than that of
the eastern coast of Bangladesh. This difference may be because of uplift or subsidence of land mass in different
parts (SAARC, 2003). Although Singh (2002) noticed that this difference is mainly due to the subsidence of
land.
World Bank (2002), mentioned that in 2020, 2050 and 2100 sea level will rise by 10 cm, 25 cm and 1m, which
will be affected the 2%, 4% and 17% of total land mass of Bangladesh respectively. Whereas, sea level in
Bangladesh coast will rise about 1.5 m by 2030, that will cause about 16% of total land mass to go under the
water and affected 17 million people who are living along the coastal line [2].
4.3 Extreme sea-level rise in Bangladesh and its impacts
Due to the rapid climate change, Earth is experiencing extreme sea-level rising. Here, the word “extreme”
means the unusual and unexpected sea level change and its catastrophic impacts on various regions of the world.
Because Bangladesh is located on a delta where it subsides each year and lots of people are living on this delta
will badly be affected by sea-level rise. Also this region is under the impact of cyclonic storms and monsoon.
These factors increase the vulnerability of this country to the sea-level rise. High sea levels also changes the
river flows by slowing down the drainage to the sea and causes catastrophic floods in Bangladesh.
According to SAARC Meteorological Research Council (SMRC) studies, sea level rise in Bangladesh during
the last 22 years is much higher than last 100 years global trend [13]. But this sea level rise rate is not only due
to the climate change it is also due to subsidence of the delta [14]. Actually most of the sea level rise in
Bangladesh is due to subsidence of land [15]. But the contribution of sea level rise due to climate change in this
region is non-negligible. Three different stations in different locations show different sea-level raises in
Bangladesh such as; 7.88 mm, 6 mm and 4 mm [16].Global sea-level rise during the last century’s 1-2 mm per
year which is lower than Bangladesh rate [17].There is already significant sea-level rise in Bangladesh. Even
now Bangladesh has been faced some problems because of sea level rise. But in the future all the projections
predict higher sea levels which will cause more dramatic impacts in this region (Fig. 2). Based on some different
reports for Bangladesh such as; IPCC and NAPA predictions are 14, 32 and 88cm sea level rise for the years
2030, 2050 and 2100, respectively [18]. Some of the impacts of sea-level rise are summarized below.
4.3.1 Salinity intrusion:
Sea level rise in the coastal zone of Bangladesh cause significant salinity increment on the water sources. This is
a serious problem because it affects agriculture and ecosystems, which we also mention in the following parts.
Salinity intrusion problem in Bangladesh is not dominated at the same rate all the year. It is mostly efficient in
dry season which is in winter. It has also been affected in rainy season but in this season only 10% of the land is
affected. However in dry season 40% of land has been affected by salinity intrusion. Increased sea levels affect
salinity by the ingression in the rivers and this decreases fresh water contamination of rivers. This increased
salinity of rivers will increase ground water salinity at the same time. This is the explanation of salinity intrusion
in rivers and ground water. There is also increased salinity in the soil due to increased evaporation in dry
winters. We should consider that the salinity intrusion in soil is also due to sea level rise which is mostly

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affected by the saline ground water in winter. The other factor that increases the intensity of saline intrusion is
tidal surges [16].
Fig. 2. Future sea-level predictions for the coastal zone of Bangladesh (1m and 3 m); Source: Reference [19]
In the coastal zone of Bangladesh there has already impact of salinity intrusion due to sea level rise which
causes big problems. Especially in dry season saline water penetrates 240 km inlands of the Bangladesh [16].
Salinity intrusion has serious impacts on many areas such as agriculture, fisheries, surface water, ground water,
soil, ecosystem and etc. It affects agriculture mostly in dry seasons by causing increased irrigation of products
with saline ground water because of not enough rain. However, watering with saline ground water decreases the
productivity. Currently there is salinity intrusion problem in the some parts of coastal zone but in the future it
will be more serious where its impact will reach more inlands [16]. Salinity of ground water will influence
humans negatively by causing serious drinking-water scarcity. In consequence of increased salinity on ground
water, serious diseases will arise. Food productivity loss will cause nutrition disorder and will play an important
role on human’s health [2].
4.3.2 Impacts on agriculture:
Sea level rise impacts on agriculture are significant in Bangladesh because half of the population’s economy
depends on agriculture and 83% of population’s livelihood comes from agriculture. With an increased climate
change salt intrusion will increase significantly. If the sea level rises by 45 centimeters, it’s been expected to
lose up to 15,600 square kilometers of land [1]. Salinization of ground water and soil due to sea level rise will
directly affect the agricultural production in the coast of Bangladesh. Rice production has already decreased in
the coastal zones of Bangladesh due to decreased soil yield [2]. According to World Bank (2002) increased
salinity (due to 0.3 meters sea level rise) will cause a net reduction of 0.5 million metric tons of rice production.
As it mentioned before fresh water salinization will decrease rice productivity. Besides rice agriculture the
coastal zone is also important for other goods such as oil seeds and vegetables. These products are also under
risk of decreasing productivity because of salt intrusion [2]. Also sea level rise will increase storm frequency
and more violent storms will cause catastrophic flooding.
4.3.3 Impacts on ecosystems:
Impacts of sea level rise on ecosystems can be classified in three, such as; wetland loss, salinity increment and
beach erosion [19].
The coastal zone of Bangladesh has a very rich variety of species both for plants and animals such as mangrove
forests, Sal forest, dipterocarp forest, bamboo bushes, freshwater swamp water forest, Bengal tiger, turtles, birds
and etc. [14]. There will be lots of negative impacts on these species due to climate change but in our study we
will focus on the impacts of sea level rise on these species. Salt intrusion will affect some species which can’t
survive from increased salinity of ground water and soil. As a result of salt intrusion these areas are being
converted into saline water fields day by day. It is obvious that the salt intrusion will cause enormous loss of
biodiversity [2]. World Bank (2000) predicts that, in case of 1 meter sea level rise, Sundarban mangrove forests
will be completely lost which is a very rich forest indeed. Even an increase of salt concentration in the soil and
water will affect the habitat pattern of these forests [2]. Moreover, due to increased salinity in the inlands,

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aquatic organisms will move inlands. Sundarban is not only a simple forest at all; it includes lots of flora and
fauna such as Bengal tiger which will be under threat of extinction from this forest [2]. Besides, increase of sea
level will decrease photosynthetic productivity of marine corals and hence decrease the growth of corals [2].
4.3.4 Vulnerability:
It is important to explain the meaning of the word “vulnerability” in order to find out the reasons of extreme sea
level rise impacts in Bangladesh. Vulnerability arises from the relationship between humans and their
environments in the face of disasters [20].
Because being a low-lying country Bangladesh is highly vulnerable against the sea level raise. 80% of the
country experiences flooding. Also, the economy of this country is not developed. Agrawala (2003) stated that,
combination of low-level development with climate and topography causes high vulnerability in this country. It
is a densely populated country and this high population rate also increases the risk of mitigation to other
countries under any threats of sea level rise. 1/5th of the country’s economy is based on agriculture which will be
affected by sea level rise.
4.4 Some solutions for Bangladesh
Due to the impacts of sea level rise that are mentioned above, some urgent actions should be taken to solve these
problems in Bangladesh. Therefore, such solutions like adaptation and mitigation should be considered.
4.4.1 Adaptation:
Due to the global climate change sea levels will continue to increase and because of that adaptation process in
Bangladesh is very important. However, it should be considered that the adaptation process requires long term
and expensive studies [16]. Some of these adaptation strategies can be specified here. These are:
 Agricultural habitats can be changed. Improvements can be done in agricultural techniques.
 Crop patterns can be changed and high quality crops can be used for yield increment
 Planning can be done: embankment building to prevent flooding into the agricultural land, settlements.
 After salinity intrusion, usage of the area can be changed. For example agricultural land can be converted
into fish farms.
 Settlements can be moved to safety places.
 People who are living in the coastal zone should be prepared to the disasters due to sea level rise.
 Regular surveys should be done in the fresh water to detect diseases. If some diseases germs detected in
the fresh water urgent cautions should be taken to stop the epidemic of disease.
 If the capacity of country can be increased the vulnerability will decrease. This can be only done by
economic recoveries. More capacity means less vulnerability [16].
 International organizations should inform people about the effects of population growth in the coastal
zone and arrangements must be done to limit population growth (IPCC, 1990).
 International and national research programmes should be involved to observe impacts of sea-level rise in
the coastal zone of Bangladesh (IPCC, 1990).
4.4.2 Mitigation:
It is clear to all that global warming has increased the level of ocean water and the main cause of global
warming is emission of greenhouse gases to the at mosphere. IPCC Fourth Assessment Report (2007) Working
Group III suggested some mitigation strategy for all country to reduce the greenhouse gas emission. Such as:
 Supply and distribution of efficiency should be improved. Switched fossil fuel to gas, nuclear power,
renewable power (hydropower, solar, wind geothermal and bio-energy).
 Mode of transport system should be shifted from road transport to rail and public transport system.
 Stop deforestation by increasing more afforestation.
 Improve forest management system and produce more bio-energy by using forestry products.
 The function of lighting and day lighting can be used for electrical appliances, heating coupled with
cooling devices, improved cook stoves also insulation, passive and active solar design in order to heat
and cool, substitute refrigeration fluids, recovery and recycle of fluorinated gases.
 Crop and grazing land management must be improved in order to get more soil carbon storage,
reestablishment of cultivated peaty land and degraded lands, improved rice cultivation techniques and
livestock and manure management to reduce CH4 emissions, improved nitrogen fertilizer application
techniques to reduce N2O emissions.
5. Conclusion
In Bangladesh the reasons of extreme sea level rise is due to subsidence of land, storm surges and flooding as
well as thermal expansion and ice melting. Sea level rise rate is higher than the global trend because of its local
characteristics. So, while the global trend of sea level rise is 1.8 mm per year (IPCC, 2007), it is averagely 7 mm
per year in Bangladesh [16]. This extreme sea level rise in Bangladesh has serious impacts on important areas
such as; salinity intrusion, agriculture and ecosystems.

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Due to increased salinity intrusion 10% more land will be affected in Bangladesh (It is now 10% in rainy season
and 40% in dry season). Salinity intrusion will also affect agriculture and ecosystems. It will decrease the
productivity of agricultural land. Some species will disappear from ecosystems due to increased salinity and
serious loss of biodiversity will be experienced. Humans will seriously be affected by water scarcity due to fresh
water exiguity. Moreover, it will cause socioeconomic problems in Bangladesh [16].
It is obvious that, there will be huge economical loss due to impacts of sea level rise on agriculture. The main
problems for agriculture on the coastal zone due to sea level rise can be summarized as; salt intrusion into soil
and ground water, decreased soil quality, fresh water scarcity, increased flooding due to increased cyclonic
storm frequency and loss of land [2]. Ecosystems will be affected in three ways. These are wetland loss, salinity
increment and beach erosion [19]. Here it mentioned two solutions against these impacts. These are adaptation
and mitigation.
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