Climate Change: Comparing effects on coastal and urban regions of
Bangladesh
Zebun Nasreen Ahmed1, Fahmid Ahmed2 and Samina Mazumdar3
Department of Architecture, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh
Abstract.: Climate change is an undeniable reality of the present. Studies show that among the most
vulnerable of the World's localities are the coastal fringes of the tropics, of which Bangladesh happens to be
one of the most threatened. A study has been undertaken comparing the changes of climate in the Dhaka
region over a time span of 50 years. The Dhaka region which lies approximately 200 km inland from the
coast of the Bay of Bengal, has been considered as representative of the deltaic plain of Bangladesh,
presenting averages to the slightly more extreme conditions of the north of Bangladesh and the slightly less
severe conditions of the coastal belt. The main effects of climate change are then investigated, while their
reflection on the environment and lifestyles are analyzed. These changes are bringing about migrations,
affecting the livelihoods of populations, and changes in settlements, and in the ways that the populations
cope with the environment. Dhaka, the capital city of Bangladesh, is one of the most populated metropolises
of the present-day World. With environment related problems more and more of the coastal and other
affected populations are migrating to the city in search of work and shelter. This study looks into a particular
region in the south of Bangladesh, Kuakata, and the settlement patterns of that coastal region and includes a
summary of suggestions that can be undertaken to make settlements less vulnerable to the climate, and thus
to stop environmental migration. Important questions require answers if one is to develop understanding of
the social and environmental issues related to climate change and about ways in which settlement patterns
are evolving to address these demands, adapting to new and very different surroundings. The discussion
concludes with a comparison of the settlements of these diverse groups of populations, those in the coastal
belt and those in the metropolis.
Keywords: climate change, settlement patterns, climate response
1. Introduction
Bangladesh has in recent years seen a number of natural disasters, and has thus been categorized as one
of the most vulnerable regions in terms of the effects of climate change and sea level rise. While the effects
of climate change are reported in various publications, one of the social effects of this phenomenon is urban
migration[1], which happens to be the focus of this paper. The number of environmental refugees is expected
to reach 20 million by 2050, when 20 percent of the coastal regions of Bangladesh becomes submerged due
to sea level rise [2].
1
Professor. BUET. +8801715042277, znahmedarch@gmail.com
2
Assistant Professor, BUET. +8801720343763, fahmid_shishir@yahoo.com
3
Lecturer. BUET. +8801190799713, samina123@gmail.com
2. Examining climate data and determining extent of change
Climate data of two periods have been examined [3]. Data from the early urbanization period (19611980)[4], and the immediate past decade and a half (1997 – 2010)[5], where the effects of densification and
rampant urbanization are only too evident, have been compared, to determine the extent of climate change in
Bangladesh. From these data, the changes in the mean maximum temperature, mean minimum temperature
and relative humidity values for the three representative months [6] of April (hot-dry season), July (warmhumid season) and January (cool-dry season). This comparison is summarized below.
Figure 1: Comparing April temperatures in the two distinct data sets
The graphs depicting April conditions for the two data sets (Figure 1) indicate that:
In general, taken as a group, mean maximum temperature (Tmax) has reduced in recent times. This seems
to contradict claims of global warming, but may be due to increased shadowing in high density settlements.
In the immediate past three years or so however, the trend seems to be towards higher temperatures.
Minimum temperature (Tmin) values are also higher in the recent data, with highest values shown in the
past three years, indicating an escalating trend.
The diurnal variation in the recent data is higher, indicating lower relative humidity (RH) values. At high
temperatures, this may bring slight relief in terms of thermal comfort.
Comparison for July (Figure 2), representative of the warm-humid season, in the two data sets shows:
Figure 2: Comparing July temperatures in the two distinct data sets
During the 1961-80 period, the variation of mean Tmax was low, staying on average below 310C, and this
trend was also notable in the early parts of the second data set. Higher mean Tmax values were, however,
recorded in the immediate past few years, with this level rising above 330C, showing a distinct higher trend
and possible global warming effect.
Mean Tmin values are almost always higher in the second set, bringing the overall band of temperature
range experienced to higher levels.
The lower diurnal range, indicates higher RH levels and increased thermal discomfort at these high
temperatures. As tolerance for high temperatures decreases rapidly at high RH levels, due to compromised
evaporation, alternate means for cooling need to be instituted.
Finally examination of the two data sets for the cool-dry season (Figure 3) reveals the following:
Contrary to global warming expectations, mean Tmax during recent years has actually reduced. Mean Tmin
values, however, are higher in the second data set, showing that the diurnal range in recent years has
reduced, indicating higher RH values. The initial examination of mean Tmax and Tmin values shows increased
RH for two of the three seasons, requiring special provisions for thermal comfort. The data on average RH
from the two data sets (Figure 4) corroborates this increase of humidity inferred from the temperature data.
Figure 3: Comparing January temperatures in the two distinct data sets
Wind data reveals that, while speed has reduced in the warm periods of the year on average (April and
July) there has been an increase in January. Therefore, when air movement has ability to cool, during hot
spells, the wind has decreased, while in the winter, higher wind speeds increase discomfort, due to wind chill
effects. Thus the climate is perceived as warmer during the warm months, and colder during winters.
Figure 4: Comparing RH and Wind speed values for the two data sets
Precipitation was not compared in the above study. However, recent reports on rainfall in the past year or
so, suggests that there has been unprecedented rainfall in the immediate past few years, with the
intensity/concentration increasing in shorter durations.
Natural disasters have also been reported to be increasingly frequent and severe in recent times. Thus
episodes, such as Sidr and Aila have, in quick succession, hit coastal areas of Bangladesh, and produced
inundation, increased salinity, sustained misery and prolonged migrations. This also becomes a big factor in
lifestyle and livelihood changes[7], mainly from fishing and agrarian, to seeking urban work in occupations
that are on offer on a daily basis, rather than on choice of the worker. The next section discusses the
implications of the changes that have been noted in the variables of climate on the built environment.
3. Implications of change on buildings
The critical design period for the warm tropics is the warm and hot months. April, with its high
temperatures, and July, with its moderately warm temperatures and high relative humidity, are periods which
will be discussed in this paper. If buildings can be made comfortable during these periods, then they are
likely to provide adequate comfort for more than nine months a year.
Rise in mean Tmax that has been noted in April, shows that this value is often closely approaching skin
temperatures. Under such circumstances only air movement can provide some thermal relief. The recent
lower humidity level in this month can somewhat relieve the situation, if air movement can be induced.
However the data comparison shows decreased natural wind speeds during April, so buildings need to
provide facilities, to capture available breeze, even more efficiently, than in earlier times.
Increased rainfall and flooding affects durability of materials. More durable materials are needed to
withstand the weathering effects of humidity and water logging. Plinth heights need to be raised. Lower parts
of buildings may require stilts, and provision has to be kept for raised storage space, which can, in the event
of flooding, be used as temporary shelter for the occupants.
If direction of wind is seen to change, orientation of building must be reconsidered. If this conflicts with
the sun position, i.e. if the wind flow, which should be encouraged, coincides with the solar position, which
can create overheating, and should thus be discouraged, then shading without obstruction needs to be given
due consideration. Moreover, if wind speeds become too high from the main wind flow direction, then
reinforcements to stop storm damage will have to be installed for preventing storm hazards.
But along with climate change, construction materials and technology have also developed. The intention
is to strengthen buildings by using materials which are stronger, more durable and weather proof, thus
making the houses less vulnerable. However, materials are thereby becoming less permeable - so wind
permeability is decreasing - since that was one of the only ways of natural cooling, this is likely to seriously
affect the comfort potential of settlements.
In the next section, settlements of the study area Kuakata in South Bangladesh, is discussed, followed by
those in urban Dhaka, which in many cases are occupied by these same people.
Figure 5: Settlements in Coastal areas of indigenous materials
4. Settlements in Coastal Region of Kuakata
The settlement patterns of coastal areas in South Bangladesh have some unique characteristics, which
differ from other parts of the country. It is mostly fishermen, who live in the hard line of the coast, while a
few are involved in agriculture. The peripheral area is often inundated due to surge.
Traditional structures are environmentally responsive, and made with easily available local materials.
Studies show that the locals have developed an indigenous perception and prediction strategy for cyclones
and, thereby possess effective survival strategies in times of cyclones[8]. Most of the houses in the area are
constructed over stilts, made of bamboo or wood. Some of the structures are built on raised plinths, but these
are mostly located in more inland areas, rather than on the hard line coastal areas. Thatched roof, with woven
bamboo matting walls, are very common for these structures, where the basic structural framework is also of
bamboo or wood, the latter for the slightly more affluent.
In recent times, reinforced cement concrete (RCC) pillars are making inroads into the traditional
technology in some areas, where non load bearing walls and roofs are of corrugated iron (CI) sheets. The
new structures of RCC and CI sheets are not environmentally responsive. The locals traditionally used
bamboo cross beams to protect the building structure from high winds (Figure 5). The indigenous structural
system remains stronger in term of protection against wind, due to techniques of structural elements and
different kinds of cross-bracing of building structures, which is evident from different research[9].
Fishermen live rather temporarily in another kind of settlement in these coastal areas,. Normally, the
occupants of these houses have more permanent houses inland, for their families. The temporary fishing
villages, inhabited for seven to eight months for fishing, are found in extreme remote and vulnerable areas.
At the end of the fishing season these highly vulnerable villages, which grow on the very edge of the sea,
become empty. These settlements are made of local materials and technology, with minimum cost. The
structures are on stilts, due to the context, and are sometimes built in rows. It is normally these houses that
are most affected during cyclones. Urban migrants are usually from such backgrounds, being environmental
refugees. The cyclones are so severe that even permanent structures stand little chance of survival (Figure 6).
After natural disasters, many people move to nearby higher grounds, losing their livelihoods and means
of income, and often also their houses. Such people are still found living on embankments, or on higher
ground, living vulnerably. Other effected people migrate to inland parts of the country, homing in on urban
centres, for survival, where they look for a new source of livelihood. The next section deals with settlements
found in urban Dhaka, which present very different environments for these displaced people.
Figure 6: Vulnerable Settlements in Coastal areas – even permanent structures are threatened (right)
5. Migrant Settlements in urban Dhaka
Migrants from coastal areas and other parts of the country mostly find their abode in the slums of Dhaka,
situated in low-lying areas, often at the peripheral fringes of the city. These settlements lack proper
infrastructure and basic facilities, like water supply, sanitation, etc[10]. The general characteristics can be
summarized as below:
These settlements are composed of mostly extreme high density low rise temporary structures built on
stilts of bamboo or wood, to keep above the water level.
Most of the structures have CI sheets for walls and roofing, without proper windows for ventilation.
Some grounded structures can be found having brick walls, with CI sheet roofing.
There is no open space or breathing space in these settlements, in total contrast to where they came from,
and the quality of living is very poor.
In the absence of proper drainage and sanitation system they pollute the water bodies in the low
lands. The water, rainwater runoffs and leakages from drains, remains mostly stagnant, creating extremely
unhygienic living conditions.
Indisputably, conditions in urban slums is very poor, constituting a major deterioration in the quality of
life experienced by the migrants. Proper study and analysis of the vast differences between these makeshift
urban settlements, and their rural counterparts, is needed to improve their lot. It is also important to identify
ways in which people living in the threatened coastal areas can strengthen their settlements, discussed in the
next section, to decrease their vulnerability, and perhaps stem the need for migration.
6. Suggestions for coastal areas to decrease vulnerability
In vulnerable coastal areas some specific points can be considered to make them disaster resistant [11],
as this would lead to putting a stop to needless urban migration. The suggestions are placed below.
Sites above the likely inundation level should be chosen for settlements, and if unavailable, construction
should be done on stilts. In such cases, no masonry or cross bracings should be provided, up to maximum
surge level, but above this level, the stilts should be properly braced in both the principal directions. Another
option is to construct on raised earthen mounds to avoid flooding/inundation, in which case knee bracing
may be used. The stability of the building depends primarily on its foundation, which can be a shallow
foundation if on stiff sandy soil. In liquefiable or expansive clayey soils, deep foundations are recommended.
Shape should be carefully controlled as it is the most important single factor in determining the
performance of buildings in cyclones. Square plans are considered better than rectangular ones, since the
former allows high winds to go around them, while the rectangle performs better than the L-shaped plan. In
case of rectangles, it is advisable to keep the length not more than three times its width.
Figure 7: Migrant Settlements in Urban areas of CI sheeting (left) – with no fallback in case of flooding (right)
Roof pitch is also an important factor, determining the stability of a house. In order to lessen the effect of
uplifting wind forces, the roof pitch should not be less than 22º. Hip roofs (charchala) are best, performing
better than gable roofs (dochala). If the rafters are not secure, the ridge can fall apart when strong winds pass
over the roof - and if the roofing material is of CI sheeting, they must not be too thin, as tearing makes them
potential hazards in any storm. A minimum thickness gauge of 24 is recommended.
Patios and verandahs, which experience high wind pressures, should be built as separate structures,
rather than as extensions of the main building, and should be kept short and small. This suggestion, however,
conflicts with the social needs for semi-outdoor spaces.
Openings in general are areas of weakness and stress concentration, but are needed essentially for light
and ventilation. In load bearing walls, openings should not be located within a distance of h/6 from inner
corner, where ‘h’ is the storey height to eave level. Well designed thicker glass panes or designs for reduced
panel size is needed to restrict damage/injury when glass is broken during storms. Glass panes can also be
strengthened by pasting thin film or paper strips. Overhangs/shades are subject to uplifting forces, and should
not be more than 450mm at verges or eaves.
7. Analysing the differences and their impacts
Most environmental refugees are people who have migrated from different parts of the country, and once
arriving in the city are involved in informal sector employment, like rickshaw pulling, day labour, household
worker, etc, marking distinct changes in their livelihoods and lifestyles. The social structure in these
settlements is also a complete contrast from that in their original village. In terms of their settlements the
following points are significant.
Change of materials, from indigenous locally grown low-impact organic materials, to more permanent,
imported and non-permeable materials, is one of the most important differences between the vernacular
settlements found in coastal regions and that in Dhaka’s urban situation. Thus we see a shift in the structural
material, from bamboo and wooden joists, to concrete and brick and CI sheets. In case of walls, the bamboo
woven mats, generally used as walls of the vernacular house, are replaced by CI sheets, or brick. The
changed thermal capacity of these two house types create quite different conditions in the interiors.
Windows in vernacular houses are mere gaps in the woven mats, with covers to protect from rain and sun
penetration, as and when needed. They thus allow maximum wind flow, and help keep interiors airy and of a
temperature similar to outdoor shade temperatures. The glass/CI sheet (Figure 7, left) windows of urban
regions, however, are more impervious, and make interiors markedly different from exteriors.
Roofs are the most important modulators of internal climate, as in the tropics, this is the surface that
receives the highest solar radiation [12]. This is why the roofing material is one of the key factors for
determining the state of the indoor climate of low rise built forms in the tropics. The shift from thatch of
coastal areas, to CI sheeting in urban settlements, increases heat gain.
Lack of stilts in some cases (Figure 7, right) allows no fallback in case of flooding, which is a natural
occurrence in urban areas, due to changed surfaces, as there is very little seepage into the soil.
Increased proximity of buildings in the urban situation aggravates the wind flow situation further, though
in terms of mutual shading it provides some benefits, which if properly assessed may actually improve
internal climate.
In summary it may be said that the environmental conditions faced in these houses in urban areas in
comparison with the coastal area situation, vary significantly and require further in depth study. Such
understanding will give pointers to improve the situation and bring these affected people greater comfort.
8. Conclusions
Climate change is a reality that must be addressed adequately for sustainability. This paper has examined
the extent of climate change in the very recent past and has attempted to associate the effects of the different
climatic variables on buildings in the region. Natural disasters are becoming increasingly frequent due to
climate change and this is spurring increased migration of affected populations away from vulnerable areas,
notably the coastal regions of Bangladesh. In the absence of available options this migrant population is
making their abode in urban areas using the technology that is present here. But this is creating a marked
difference in their living conditions which has been discussed in the paper, as is the effect of the climate
change. These problems need to be resolved to improve the situation and to bring conditions to a reasonably
acceptable level. More research is needed to arrive at exact solutions, and awareness of the problems is the
first step towards alleviating the sufferings.
Acknowledgments
We gratefully acknowledge the Department of Architecture, Bangladesh University of Engineering and
Technology (BUET), as much of the observations that have led to the writing of this paper were gathered as
a result of studies and analysis for development and preparation of lectures for the courses ARCH 6101:
Thermal Environment and Built Forms and ARCH 133: Environmental Design I, at the postgraduate and
undergraduate levels at the Department.
References
[1] Morshed, M.M. An Assessment on the Uprooted Slum Dwellers of Dhaka City. Democracy Watch. Dhaka. 2002
[2] Hasan, M. . Salt. The Star: stories behind the news. A weekly publication of the Daily Star; Dhaka; 14 October,
2011
[3] Ahmed, Z.N. Comparison of climate data for two discrete periods for development of courses ARCH 6101 and
ARCH 133 for the Department of Architecture, Bangladesh University of Engineering and Technology, Dhaka.
2011.
[4] Bangladesh Meteriological Department, Agargaon, Dhaka, Bangladesh, 1985
[5] http://www.wunderground.com/history/airport/VGZR/2011/6/12/MonthlyHistory.html and
http://www.dhaka.climatetemp.info/ accessed September 2011
[6] Ahmed, Z.N. The Effects of Climate on the Design and Location of Windows for Buildings in Bangladesh,
unpublished M. Phil. Thesis; Sheffield City Polytechnic; UK. 1987
[7] Morshed, M.M. opcit. Table 4. 2002
[8] Hassan, T. Surviving Cyclones: The Indigenous WisdomUnnayan Onneshan – The Innovators. www.unnayan.org
[9] Haq B. Battling the storm: Study on Cyclone Resistant Housing, German Red Cross, 2nd edition, Dhaka, 2007.
[10] Ahmed, K. I. Urban Poor Housing in Bangladesh and Potential Role of Asian Coalition for Housing Rights.
Bangkok. 2007
[11] Agarwal, A. Cyclone Resistant Building Architecture, Hazard Vulnerability Reduction, GoI – UNDP, Disaster
Risk management Programme. 2007
[12] Ahmed, Z.N. Assessment of Residential Sites in Dhaka with respect to Solar Radiation Gains, unpublished PhD
thesis. De Montfort University, Leicester, UK. 1994