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ESRC Centre for Population Change • Working Paper 74 • January 2016
Sylvia Szabo
Eduardo Brondizio
Scott Hetrick
Zoe Matthews
Fabrice G. Renaud
Robert J. Nicholls
Zita Sebesvari
Sandra da Costa
John A. Dearing
E Foufoula-Gergiou
Alejandro Tejedor
Zachary Tessler
ISSN 2042-4116
centre for population chang
Improving our understanding of the key drivers and implications of population change
Population dynamics in the
context of environmental
vulnerability: Comparison
of the Mekong, Ganges-
Brahmaputra and Amazon
Delta regions
Tropical delta regions experience complex population dynamics, which are strongly
influenced by socio-economic and environmental factors. They are subject to increasing
pressure from relative sea-level rise, and because of human alterations they are becoming
more and more vulnerable to extreme floods, storms, surges, and salinity intrusion,
hazards which could also increase in magnitude and frequency with a changing climate.
In this context, understanding population dynamics in delta regions is crucial for ensuring
efficient policy planning and progress towards social and ecological sustainability. Here
we focus on examining population dynamics in the Ganges-Brahmaputra, Mekong and
Amazon deltas. Analysis of the components of population change is undertaken in the
context of environmental factors affecting the demographic landscape of the three
regions, and makes use of multiple data sources, including census data and Demographic
and Health Surveys. The results of the analysis show that the demographic trends in the
three delta regions are broadly reflective of national trends, although important
differences exist within and across the study areas. Moreover, our findings show that all
three delta regions have been experiencing shifts in population structures resulting in
aging populations, the latter being most rapid in the Mekong delta. The environmental
impacts on the different components of population change are important and more
extensive research is required to effectively quantify the underlying relationships. The
study concludes by discussing selected policy implications in the context of sustainable
development of delta regions and beyond.
Population change; delta vulnerability; Ganges Brahmaputra Delta; Mekong Delta;
Amazon Delta.
Sylvia Szabo is Research Fellow at the University of Southampton, UK.
Eduardo Brondizio and Scott Hetrick are from the Department of Anthropology at the
Anthropological Center for Training and Research on Global Environmental Change and
the Ostrom Workshop, Indiana University, USA.
Zoe Matthews is Professor of Global Health and Social Statistics at the University of
Southampton, UK.
Fabrice G. Renaud and Zita Sebesvari are from the United Nations University, Institute
for Environment and Human Security, Bonn, Germany.
Robert J. Nicholls is from the Engineering and the Environment Department at the
University of Southampton, UK.
Sandra da Costa is from the Instituto de Pesquisa e Desenvolvimento at the Universidade
do Vale do Paraiba (UNIVAP), Brazil.
John A. Dearing is from the Geography and Environment Department at the University of
Southampton, UK.
Efi Foufoula-Georgiou and Alejandro Tejedor are from the Civil, Environmental and
Geo-Engineering and National Center for Earth-surface dynamics at the University of
Minnesota, Minneapolis, USA.
Zachary Tessler is from the Environmental CrossRoads Initiative at the City University
of New York, USA.
Corresponding author: Sylvia Szabo,
ESRC Centre for Population Change
The ESRC Centre for Population Change (CPC) is a joint initiative between the
Universities of Southampton, St Andrews, Edinburgh, Stirling, Strathclyde, in
partnership with the Office for National Statistics (ONS) and the National Records
of Scotland (NRS). The Centre is funded by the Economic and Social Research
Council (ESRC) grant numbers RES-625-28-0001 and ES/K007394/1.
This working paper series publishes independent research, not always funded
through the Centre. The views and opinions expressed by
authors do not
necessarily reflect those of the CPC, ESRC, ONS or NRS.
The Working Paper Series is edited by Teresa McGowan.
Website | Email | Twitter | Facebook | Mendeley
The research forms part of the international Belmont Forum project BF-DELTAS
“Catalyzing action towards sustainability of deltaic systems with an integrated modelling
framework for risk assessment” (NSF award no. 1342944). Sylvia Szabo, Zoe Matthews,
Robert Nicholls and John Dearing also acknowledge support from the project ‘Assessing
health, livelihoods, ecosystem services and poverty alleviation in populous deltas’
(NE/J002755/1) funded by the Ecosystem Services for Poverty Alleviation Programme
(ESPA). The UK ESPA programme is funded by the Department for International
Development, Economic and Social Research Council (ESRC) and the Natural
Environment Research Council (NERC).
Sylvia Szabo, Eduardo Brondizio, Scott Hetrick, Zoe Matthews, Fabrice G.
Renaud, Robert J. Nicholls, Zita Sebesvari, Sandra da Costa, John A. Dearing, Efi
Foufoula-Georgiou, Zachary Tessler and Alejandro Tejedor all rights reserved.
Short sections of text, not to exceed two paragraphs, may be quoted without
explicit permission provided that full credit, including notice, is given to the
1. INTRODUCTION .................................................................................... 1
2. MATERIALS AND METHODS ............................................................. 3
THREE DELTA REGIONS .................................................................... 7
FERTILITY, MORTALITY AND MIGRATION .............................. 11
4.1. FERTILITY ...................................................................................................... 11
4.2. MORTALITY ................................................................................................... 13
4.3. MIGRATION .................................................................................................... 16
5. CONCLUSIONS AND POLICY IMPLICATIONS ........................... 18
REFERENCES ............................................................................................ 21
Delta regions constitute dynamic ecological and social environments and are often
major contributors to national economies. While overall, deltas account for only 1%
of global land area, they are home to more than a half billion people, or ca. 7% of
world population (Ericson et al., 2006). Given the particular environmental risks faced
by tropical deltas and accounting for interlinkages between demographic and
environmental factors, it is crucial to analyse population dynamics in delta
environments to inform planning and policy making. The Millennium Ecosystem
Assessment (2005) showed that beyond provisioning ecosystem services such as food,
water, fibre and fuel, regulating and supporting ecosystem services also influence
various aspects of human development, such as health and income, and long term
sustainability of agriculture and natural resources. Trends in human well-being,
however, cannot be fully understood without considering the specific demographic
context, including evolving population structures by age and sex, and changes in the
dominant demographic drivers of fertility, mortality and migration.
Understanding population trends and dynamics in deltaic regions is especially
important in the context of global environmental change which is expected to
exacerbate the existing threats to livelihoods through e.g. sea-level rise, land
subsidence, increased storminess, flooding and saline intrusion (Nicholls, 2011, Dun,
2011, World Bank, 2000, Wong et al., 2014). In this context, the present study
examines population dynamics (growth, fertility, mortality, and migration) in three
selected tropical deltas. It draws on the theory of demographic transition and the
literature conceptualising the interlinkages between population and environment (de
Sherbinin et al., 2007, Hummel et al., 2012). According to fundamental demographic
theory (Notestein 1945; Dyson 2011; Dyson 1998), it is common for countries to
experience concurrent falling mortality and fertility levels as they progress through
the ‘demographic transition’. This is a process through which a country evolves from
high to low levels of mortality and fertility, is usually associated with increasing
longevity. The theory posits that there is a short lag between mortality decline and a
decline in fertility, and thus a short period characterized by rapid population growth.
With regard to interlinkages between population and environment, specific
components of demographic change can also be influenced by the quality of the
biophysical environment, environmental hazards and creeping processes, such as
salinity intrusion and arsenic contamination of water and soil resources.
Environmental migration contributes to population loss in an area and might even lead
to population collapse in certain areas of delta regions as settlement abandonment
becomes the main coping strategy of vulnerable households (McLeman, 2011).
Moreover, mortality rates can be affected by the quality of provisioning ecosystem
services, natural hazards and extreme weather events. For example, in Bangladesh,
3,406 people died as a consequence of Cyclone Sidr in 2007 (Paul, 2007). In many
geographical areas, deteriorating ecosystem services, such as the supply of fresh
water, were found to be positively associated with health outcomes and child and
maternal mortality (BrownCairncross and Ensink, 2013, Cheng et al., 2012, Silva,
2011). Finally, the quality of the environment can also have an impact on fertility
rates, although this relationship is more complex and not fully established. There is,
however, some evidence that environmental pollutants can negatively affect fertility,
although research findings are not consistent (Fisch et al., 2003, Foster et al., 2008).
The present study focuses on three specific delta regions, i.e. the Ganges-
Brahmaputra delta, Bangladesh, Mekong delta, Vietnam and the Amazon deltas.
These deltas were selected as they are each globally significant and encompass a
range of biophysical and social conditions. Population size, the rate of population
growth, and population distribution constitute crucial factors which are not only
affecting but which are also influenced by natural habitat. While a relatively large
body of literature examined the interlinkages between population growth and
environment (de Sherbinin et al., 2007, Hummel et al., 2012, LutzPrskawetz and
Sanderson, 2002), there is limited evidence regarding the dynamics of population
change in delta regions. Yet, approximately 10% of the world’s population live in
areas lower than 10m above sea level and the population in these low lying coastal
areas is projected to grow in all continents, especially in the developing world
(Neumann et al., 2015, McGranahanBalk and Anderson, 2007). By providing a
rigorous demographic overview of three delta regions, the study not only contributes
to the literature on delta regions, but also considers their policy implications for
sustainable development.
The study areas (Figure 1) encompass three deltaic systems, all located in
developing/transition countries. The first delta region, the Ganges-Brahmaputra delta,
Bangladesh (thereafter: GBD) is represented by 45 districts in whole division areas of
Khulna, Barisal, Dhaka, and Sylhet and most of the Chittagong division in
Bangladesh1. This is an environmentally vulnerable region suffering both from the
consequences of rapid-onset hazards (e.g. cyclones) (Kay et al., 2015) and creeping
processes, such as salinity intrusion (Clarke, Williams, Jahiruddin, Parks, & Salehin,
2015), arsenic contamination (Abedin, Habiba, & Shaw, 2012; Edmunds, Ahmed, &
Whitehead, 2015) and subsidence (S. B. Brown & Nicholls, 2015). There is extensive
evidence that multiple stressors associated with climate change place increasing
strains on the livelihoods of populations in the region. In particular, food security has
emerged as a key developmental concern (Faisal & Parveen, 2004; MEF, 2009).
The second study area is the Vietnamese portion of the Mekong delta region
(thereafter: the Mekong delta), which covers 13 Vietnamese provinces and excludes
Ho Chi Min City. As with the GBD, the Mekong delta is highly vulnerable to adverse
environmental events, in particular flooding and salinity intrusion. While it has been
recognised that fluvial floods can bring benefits for the economy, as they convey
sediment and benefit fisheries (Tri, Trung, & Thanh, 2013), flooding can also have a
disastrous effect on households’ livelihoods. Since 2000, the region experienced three
major floods (2000, 2001 and 2002); the first affecting approximately 11 million
people. As a result of this flood, 800 thousand dwellings were inundated and 55,123ha
of rice crops destroyed (Nguyen & James, 2013). Extreme weather events will
continue to occur in the region and may occur more frequently (Government of
Vietnam, 2009). In addition, climate change is likely to increase not only the risk of
flooding, but is also associated with relative sea level rise, salinity intrusion and
changes in temperature and rainfall patterns (Dang, Li, Nuberg, & Bruwer, 2014;
Nguyen & James, 2013).
Finally, for the Amazon delta (Brazil), to define our study area we combined
the parameters provided by Ericson et al. (2006), who used a 5km buffer zone around
1 The Chittagong division excludes the districts of Khagrachari, Rangamati and Bandarban.
the coastline intersecting with the first distributary, and the limits of municipalities
intersecting this buffer zone. In terms of administrative boundaries, the study area
comprises 50 municipalities across the Pará and Amapá states in the North region of
Brazil (or approximately 6% of the legal Brazilian Amazon). In 2010, our study area
contained approximately 16.5% of the total population of the legal Amazon and 18%
of its urban population (IBGE, 2010). While other parts of the Brazilian Amazon have
undergone significant environmental change during the last three decades, the delta
region has seen relatively lower levels of environmental degradation. The region has
experienced rapid urbanization and a growing economy based on forest products and
agroforestry (Brondizio, Vogt, & Siqueira, 2013). Most urban areas in the region lack
basic sanitation and other infrastructure as well as public services, which along with
some of the highest poverty rates in Brazil create vulnerable conditions for a
significant segment of the population. On the other hand, farmers in the region are
reporting increasing tidal flooding and changing salinity in coastal ecosystems, but
these changes have not been systematically documented.
In order to conduct our analyses, this paper draws on a number of secondary
macro and micro level data sources. For Bangladesh, the data used include 2010
Household Income and Expenditure Survey (HIES) conducted by the Bangladesh
Bureau of Statistics (BBS, 2011a), Demographic and Health Surveys (DHS) (Mitra,
Ali, Islam, Cross, & Saha, 1994; NIPORT, Mitra and Associates, & ICF International,
2013; NIPORT, Mitra and Associates, & Macro International, 2009; NIPORT, Mitra
and Associates, & ORCM, 2001) as well as census data. Similarly, for Vietnam, we
use the Vietnamese Living Standards Survey (VLSS), Census data and Demographic
and Health Surveys. Finally, for the Amazon we used census data from the Brazilian
Institute of Geography and Statistics (IBGE) and demographic data and human
development indices compiled by The Institute of Applied Economic Research
(IPEA) of Brazil (IBGE, 2010; IPEA, 2010). Data are aggregated at the municipal and
census sector levels for 1991, 2000, and 2010 in all three delta regions. Table 1
summarizes the demographic data sources used in the analysis.
Delta region Data source
Bangladesh Demographic and Health Surveys (DHS),
2010 Household Income and Expenditure Survey
(HIES), Bangladesh Population and Housing Census
(2001, 2001 and 1991.)
Vietnamese Living Standards Survey (VLSS), Vietnam
Demographic and Health Surveys (DHS), 2009 Vietnam
Population and Housing Census, online data repository
developed by the General Statistics Office of Vietnam.
Brazilian Institute of Geography and Statistics (IBGE;
2010 & 2014) Institute of Applied Economic Research
(IPEA; 2010.)
Cross-cutting World Population Prospects (United Nations, 2012.)
Table 1: Sources of demographic data
Figure 1 illustrates the key delta relevant population-environment gradients
and socio-environmental characteristics of the three study areas. Gradient bars,
associated with variables are shaded to represent the respective “values” of each
variable for each study area. Darker shades represent higher values. Population size
and population density are greatest in the GBD where the total population exceeded
108 million and the population density in the study area is approximately 1,280
people per km2 (Ericson et al., 2006). The proportion of delta population at risk is
highest in the Mekong delta region and so is the proportion of delta area potentially
lost by 2050 (Ericson et al., 2006). It should however be noted that in terms of
absolute numbers the greatest impact on population loss is expected to take place in
the GBD (Ericson et al., 2006). Amongst the three delta regions, the Amazon delta
has the highest proportion of urban population, while the Mekong delta is least
urbanized. In terms of environmental characteristics, saline water intrusion penetrates
further inland in the GBD and so sediment reduction is the largest compared to natural
conditions (Syvitski et al., 2009).
Figure 1: Population-environment gradients in the study areas
Notes: 1. Bangladesh Population and Housing Census (2001, 2001 and 1991); 2. Brazilian Institute of Geography and Statistics (IBGE, 2010); 3. 2009 Vietnam
Population and Housing Census; 4. Ericson et al. (2006); 5. World Development Indicators (WDI), World Bank; 6. Parry, M. L., Canziani, O. F. , Palutikof, J. P., van
der Linden, P. J., & Hanson, C. E. (2007); 7. Giri et al. (2011); 8. Syvitski, et al. (2009); 9. Syvitski and Saito (2007).
In the 20th century, all three countries in which the study areas are located, have been
experiencing rapid demographic transitions. In Vietnam, demographic transition was
reflected in considerable decline in total fertility rate (TFR), measuring the average
number of children born per woman, and improvements in infant survival rates (Ngo
et al., 2010). Bangladesh is interesting in this respect because the fertility decline has
been largely fuelled by a very successful family planning programme. On the other
hand, Brazil represents an example of a country where fertility dropped without direct
government intervention, although associated with significant sterilization rates in
public and private clinics (Cleland et al., 2006, Demeny, 2011, Siqueira et al., 2007).
In Vietnam, the rate of population growth in the country declined from 2.32%
in 1970-75 to 0.95% in 2010-15 (UN, 2013). During the same time period, in
Bangladesh the rate of population growth dropped from 1.72% to 1.19%, while in
Brazil it decreased from 2.38% to 0.85% (UN, 2013). Figure 2 illustrates the trends in
population growth in the three delta regions. In the past two decades, the Mekong
delta continued to experience population growth despite falling fertility and relatively
high out migration (Dun, 2011). The overall population in the Mekong delta increased
from around 15.5 million in 1995 to over 17.5 million in 2013 (Figure 2b). However,
the Mekong delta is one of the regions with the lowest population growth rate in
Vietnam with large spatial differences within the delta (Garschagen et al., 2012).
Similarly, in the GBD, the population size in 2011 increased by approximately 19
million people compared to 1991, which represents a 17.5 % increase in population
size over the last two decades (Figure 2a). Based on the 2011 census data, the total
population of the study area was about 108 million, comprising approximately 75%
Bangladesh’s population. Out migration combined with below replacement level
fertility rates in some districts contributes to changing population structure and
negative rates of population growth. For example, during the last two decades, in
Pirojpur district in south-western Bangladesh the population decreased by around
18.4% while in the nearby Barisal district, the population declined by approximately
14.3% (BBS, 2012).
Likewise, the Amazon delta region has experienced continuous population
growth since 1990 (Figure 2c), most of it being in urban areas of the delta. As
highlighted previously, the study area for the Amazon delta is shared by two states in
the Northern region of Brazil. To the north, the state of Amapá includes nine
municipalities, while to the south the state of Pará includes 41 municipalities within
the Amazon delta region. With approximately 4 million people, the population size of
the Amazon delta is the smallest of the three delta regions. Since 1990, the region has
experienced over 56% increase in total population growth reaching a total of ca. 4
million people in 2010 (IBGE, 2010). The majority of the population in 2010, 78.5%,
declared urban residency. However, there exists considerable variation within the
region (IBGE, 2010). The Amazon delta experienced slight decrease in rural
population from 1990 to 2000, followed by a slight increase from 2000 to 2010. The
increase in rural population reflects increasing economic importance of forest and
agroforestry products in the region, opening economic opportunities in rural areas and
motivating strong connections between rural and urban areas (BrondizioVogt and
Siqueira, 2013).
When analysing population dynamics of delta regions, it is important to
consider their population structures. In the Mekong delta region, the population aged
15 to 35 constitutes the greatest percentage of the total population, while the bottom
of the pyramid is relatively narrow indicating an aging population structure (Figure
3b). This population structure is reflected in the region’s dependency ratios, which is
around 42.3 % as compared to the national average of 44.7 % (General Statistics
Office, 2011). More specifically, the child dependency ratio of 33.8 % is relatively
low when compared to that of other regions. For example, child dependency ratio in
the Central Highlands is 50.5 % and the national average is 35.4 %. It should be noted
that the current population structure of the GBD (Figure 3a) is younger than that of
the Mekong, although it is visible that the youngest age groups (0-4 and 5-9) are
disproportionally small, which reflects recent trends in fertility decline. It should be
highlighted that during the last decade, all five divisions which fall under the study
area have seen a decrease in fertility rates accompanied by a tendency towards smaller
households. In terms of regional differences, in 2001, the smallest average household
size was 4.7 (Khulna division), while the largest household size was 5.7 (Sylhet
division) (BBS, 2011). In the Amazon delta (Figure 3c), a significant proportion of
the population is young, between the ages of 10-25. Similarly, to the Mekong and GB
deltas, the demographic profile of the Amazon delta region has been changing since
the 1980’s, partly as a result of significant fertility decline. Compared to the Mekong
delta region, the population structure in the Amazon delta has not yet reached the
rapid ageing trend; however, its overall population is older than that of the GBD.
Figure 2: Recent population growth in the (a) Ganges Brahmaputra, (b) Mekong and (c)
Amazon deltas.
Figure 3: Population structure in the (a) Ganges Brahmaputra (2011), (b) Mekong (2009) and
(c) Amazon (2010) deltas.
Fertility is the key aspect of population change, as it has arguably the greatest impact
on population structure, particularly when migration is negligible. As highlighted
previously, during the past half-century, Vietnam has undergone rapid demographic
transition with the TFR declining from 6.4 in 1960 to 1.8 in 2013 (World Bank,
2012). Today, the unmet need for contraception is estimated at 4.3% at the national
level and 3.6% for the Mekong delta region (General Statistics Office, 2011b). While
long time series are not available at the regional level, the Demographic and Health
Surveys (DHS) provide more recent disaggregated data on fertility and health
outcomes. Based on these data, it can be observed that since the 1990s the TFR in the
Mekong delta region has been continuously decreasing and is currently estimated at
1.92 (Figure 4). In terms of early childbearing, the percentage of women aged 20-27
who had their first birth before the age of 18 is 5.8% in the Mekong delta region,
while the equivalent national proportion is 3% (General Statistics Office, 2011b).
Similar to the Mekong delta, analysing trends in the total fertility rate in the
GBD reveals a decline from 3.5 children per woman in 1993 to roughly below 2.5 in
2011 (Figure 4). Fertility decline has been more pronounced for women from
wealthier households than for women from poorer households. The average total
fertility rates in the coastal divisions of Khulna and Barisal are below the national
average except for Barisal district. The lowest fertility rates amongst the coastal
districts are observed in Satkhira and Barguna districts with TFR 1.56 and 1.59
respectively (BBS, SID & Planning 2012). Finally, since the early 1990s the Amazon
delta region has experienced the most rapid decline in TFR with a drop in TFR from
over 6.1 children per women in 1991 to 3.3 in 2010. This fast decline in fertility
mirrors the general trends in Brazil which are explained by a combination of
government programs, migration from rural to urban areas, and social-cultural change
regarding women’s rights and household roles (Siqueira et al., 2007). This trend
started first in the urban areas of South and South East regions and then spread
gradually to the rest of the country (Siqueira et al., 2007). A key feature of the process
was the reliance on irreversible methods of contraception, such as female sterilization.
In 1996, in Northeastern states, 51% of married women between 15 and 49 reported
having undergone sterilisation (Caetano, 2001), a trend confirmed for areas of the
Northern region by Siqueira et al (2007).
Figure 4: Recent trends in TFR in the Mekong, GB and Amazon delta regions.
Source: BBS, IBGE and General Statistics Office (GSO), Vietnam.
These past trends indicate that future delta populations are likely to drastically
change and see smaller households with a greater proportion of elderly dependents.
This predicted change is expected to be most rapid in the Mekong delta. Vietnam saw
a decrease from an average household size of 4.8 in 1989 to 3.8 in 2009 (General
Statistics Office, 2011a) and in 2009 household size in the Mekong delta was
estimated at 3.9 (Figure 5). The trends towards smaller households are accompanied
by a rising age at marriage and rising divorce rates. The ratios of divorce/separation to
marriage are the highest in the Mekong delta and Southeast regions, which is likely to
be associated with high rates of out-migration. Comparatively, in the GBD, there has
been a trend towards smaller household size, although there exists considerable inter
divisional differences. In our study area, an average household size varies from 4.3 in
Khulna to 5.4 in Sylhet (BBS, 2011b). It should be highlighted that during the last
decade, all five divisions which fall under the study area have seen a decrease in
household size. In 2001, the average family size in the delta region was 5.1 while in
2010 in was 4.8 (BBS, 2011b). Finally, in the Amazon delta region the decline was
even more rapid, although an average household is larger than in the Mekong delta
region. In 2000, an average household size in the Amazon delta was 5.0 and it has
declined to 4.5 in 2010 (Figure 5).
Figure 5: Change in mean household size across the three study areas.
Source: BBS, IBGE and GSO, Vietnam.
Mortality constitutes a second aspect of population change and is closely related to
human health and overall well-being. With regards to mortality trends, Vietnam has
experienced considerable improvements in life expectancy, reducing child mortality.
At the country level, life expectancy was 59.1 in 1960 (World Bank, 2012) and
increased to 72.2 years in 2005 and 73.1 years in 2013 (General Statistics Office,
2014). In the Mekong delta region, life expectancy increased from 73.4 in 2005 to
74.4 in 2013 (General Statistics Office, 2014) (Figure 6). Concerning child mortality,
infant mortality rate (IMR) in the Mekong delta region is the second lowest regionally
(after the Southeast region). The IMR in the Mekong delta is estimated at 12.0, while
the national average is 15.3 (General Statistics Office, 2013). It is difficult to examine
to what extent mortality trends have been affected by environmental factors. The
interlinkages can occur at two levels: first, through direct impact of natural hazards on
human life, and second, through the effects of the quality of environment, such as
water quality. Between 2001 and 2010, natural disasters affecting the country were
responsible for death of 9.5 thousand people (Government of Vietnam, 2011).
Between 2000 and 2002, 1,144 people were killed due to floods in the Mekong delta
region (Central Committee for Flood and Storm Control, 2015). Children were found
to be particularly vulnerable to floods, especially in poorer households were parents
worked outside often leaving children without supervision (Nguyen & James, 2013).
Secondly, indirect environmental effects on mortality rates include the quality of
water and sanitation, which are associated with water borne diseases, such as cholera
and typhoid and paratyphoid fevers. Water quality in the frequently populated smaller
waterways of the Mekong delta is relatively poor, regardless of the sources exploited
(surface-, ground-water, rain water, piped water), with contamination by pesticides
(Chau, Sebesvari, Amelung, & Renaud, 2015; Toan, Sebesvari, Blasing, Rosendahl,
& Renaud, 2013), nutrients, metals, salinity and microbial organisms (Wilbers,
Becker, Nga, Sebesvari, & Renaud, 2014; Wilbers, Sebesvari, Rechenburg, &
Renaud, 2013; Wilbers, Sebesvari, & Renaud, 2014). In peri-urban and rural regions
of the Mekong delta, large portions of the population are directly exposed to polluted
water and consume polluted water with treatments that do not allow eliminating all
contaminants (Wilbers, Becker, et al., 2014; Wilbers et al., 2013; Wilbers, Sebesvari,
et al., 2014).
Similarly, in the GBD, environmental factors and climate change can have an
important direct and indirect effect of human mortality. It should be stressed that
Bangladesh as a country has achieved significant progress in a number of health
indicators, despite its relatively poor economic situation (Chowdhury et al., 2013).
Current life expectancy in Bangladesh is estimated at 69 years for males and 71 years
for females, an increase by 9 and 12 years respectively since 1990 (WHO, 2014)
(Figure 6). At the same time, however, maternal and child mortality rates are
worryingly high. For example, based on the World Bank data, maternal mortality ratio
is 170 per 1000,000 live births, which is similar to that of Pakistan and Cambodia and
considerably higher than maternal mortality rate (MMR) in Vietnam and Brazil
(World Bank, 2012). The population of the GBD is particularly vulnerable to
cyclones, especially in coastal areas. It has been estimated that during the last 50 years
approximately 718 thousand people died due to cyclones (Haque et al., 2012).
However, the death toll has fallen dramatically and in 2007, 4,234 people died as a
result of cyclones compared to 500 thousand deaths in 1970 (Haque et al., 2012). This
reflects improved early warnings and provision of a network of cyclone shelters. In
addition to their direct effect, i.e. the loss of human life, cyclones affect the quality of
water and increase the risk of disease transmission, in particular in resource poor
areas. They can also have a post disaster impact on mental health by increasing the
risk of stress and depression (Haque et al., 2012; Shultz, Russell, & Espinel, 2005).
Finally, the population of the Amazon delta region experienced a rapid
increase in life expectancy reaching 71.8 years in 2010, an increase by 7.2 years since
1991 (IPEA, 2010) (Figure 6). Overall, life expectancy is slightly higher in the Amapá
state, although trends between both states (Pará and Amapá) are quite similar (IPEA,
2010). Infant mortality rate remains high (21 per 1,000) although it has declined more
than twofold from 49.7 in 1991. This regional IMR is considerably higher when
compared to the national IMR, which has been estimated at 15 in 2010 (World Bank,
2012). According to a recent study by the International Institute for Environment and
Development (IIED) (Viana, Viana, Euler, Grieg-Gran, & Bass, 2014), the infant
mortality rate in Amapá state is the highest in Brazil. In the Brazilian Amazon region,
natural disasters, in particular floods, are associated with environmental and health
impacts, including loss of life, however disaggregated numbers are difficult to obtain
(de Resende Londe, Pellegrini Coutinho, Torres Di Gregório, Bacelar Lima Santos, &
Sorian, 2014). In this region, health problems have also been associated with the fast
pace of urbanization accompanied by poor infrastructure. Health challenges included
infectious diseases, such as malaria, in particular in peripheral areas bordering forests
(OPA, 2010). Perhaps, the largest impact of environmental change can be noted in the
case of migration.
Figure 6: Recent trends in life expectancy in the Mekong, GB and Amazon delta regions.
Source:World Development Indicators (WDI), IBGE and GSO, Vietnam. For GBD national data
were used to approximate trends.
Migration is a key element of population change in all three study areas, with the high
environmental vulnerability of tropical deltas potentially being an important factor. At
the same time, due to its unpredictability, migration is also the most difficult part of
demographic modelling. The Mekong delta region is exposed to environmental
hazards with extreme weather events leading to frequent flooding which affects
people’s livelihoods (Dun, 2011; Nguyen & James, 2013). In addition, slow onset
hazards such as salinity intrusion continue to pose a severe risk to water and soil
quality and thus to water supply and agriculture. Climate change is likely to
exacerbate the existing risks and thus further affect future population distribution. Out
migration from the environmentally vulnerable areas is a widely recognised coping
strategy (Rayhan, 2008). Seasonal migration to the cities can provide income during
the times of distress. For example in the Thnh M Tây commune in An Giang
province, there were 5,000 seasonal migrants reported in 2009 (Nguyen & James,
2013). Between April 2012 and April 2013 there were a total of 121,443 out migrants
from the Mekong delta region, with most of them moving to the Southeast region
where Ho Chi Minh City is located (General Statistics Office, 2013). As per the above
mentioned report, the net migration rates in the Mekong delta region are the same for
males and females. Within the Mekong delta region, Bc Liêu Province reported the
highest out migration rates (-14.2 for males and -13.5 for females) (General Statistics
Office, 2013).
Similar to migration trends in the Mekong delta region, internal migration in
the Bangladeshi GBD is an important demographic and social phenomenon.
Environmental shocks combined with economic vulnerability of large strata of the
society are the key push factors affecting relatively high out migration rates in coastal
districts. A recent report by UNDP pointed out that 40 out of 64 districts have been
identified to be environmentally at risk (Marshall & Rahman, 2013). High out
migration, in particular from rural locations contributes to creation of large slum areas
and informal settlements in cities. Because of limited or no income generating
opportunities, migration to cities is often perceived as a coping strategy for the rural
poor. In addition, crop losses or damage caused by natural hazards further exacerbate
the existing social vulnerabilities. In Bangladesh, the number of life time migrants
increased from 950 thousand in 1950 to 12,773 thousand in 2004 and out migration
from rural to urban areas grew from 7.3 per 1,000 in 1984 to 25.9 per 1,000 in 2010
(BBS, 2011b). As is the case in other delta regions, climate change, and in particular
sea-level rise, are projected to have negative impact on households’ livelihoods,
which is likely to increase the volume of out migration in the future (Mallick & Vogt,
Migration dynamics in the Amazon delta show interesting patterns. Based on
the analysis of the data for the period 2001-2007 originating from the National
Household Survey (PNAD), the state of Pará has consistently experienced high levels
of out-migration. In contrast, migration patterns in Amapá have been highly volatile
with only some years showing net out-migration flows (Ferreira-Filho & Horridge,
2010). Nevertheless, recent research reports that over 28% of the current population in
Amapá originates from outside of this state which may explain the rising trends in
population growth (Viana et al., 2014). Another body of research highlights that in the
Amazon delta, similar to other delta regions, migration dynamics are largely
intertwined with urbanisation. The difficulty of categorising and quantifying these
migration trends is related to the fact that a large proportion of migration includes
circular movements (Padoch et al., 2008).
This study aimed to investigate the dynamics of population change across three
delta regions: the Ganges-Brahmaputra, the Mekong and the Amazon deltas, as
defined in section 2. In order to achieve this goal, we analysed the trends in
population growth, population structure and specific components of population
change (fertility, mortality, migration). Several conclusions can be drawn. Firstly, our
results suggest that, consistent with national averages, fertility rates in the delta
regions have been steadily declining, falling below replacement levels in some
geographical areas, such the Khulna and Barisal districts in south-western
Bangladesh. This trend, combined with increasing life expectancy, improving child
mortality rates and migration dynamics might imply that in the longer term population
in delta regions are likely to stabilise or even decline, as recently projected for several
coastal districts in Bangladesh (Szabo et al., 2015). This is contrary to general
expectations of expanding coastal populations and coastal cities (Neumann et al.,
2015), and hence is worthy of investigation in other deltas. Secondly, while overall
the demographic trends in the deltas follow national trends, important differences
exist within study areas.
As highlighted above, total fertility rates vary considerably within the same
regions, with some geographical areas, such as the Khulna district in the GBD,
already experiencing below replacement fertility rates. Additionally, our results show
important differences in migration dynamics across the study areas, which will
influence future population size and distribution at the regional and national levels.
Thirdly, our findings suggest that all delta regions have been experiencing shifts in
population structure resulting in aging populations, with the most rapid changes
occurring in the Mekong delta. Finally, while environmental impacts on population
trends and dynamics in the delta regions are hardly contestable, they remain difficult
to quantify. Future research should therefore consider ways in which these
associations could be modelled (Nicholls et al., 2013, Lazar et al., 2015).
Although the present study advances knowledge in the area of population and
environment, at least two caveats should be acknowledged. First, this study did not
account for the differences between internal and international migration, and these
differentials will have implications for sustainable development. In addition to the
impacts of changes in population distribution, the migrants’ destination has important
consequences, including in terms of remittances they are likely to send home. Second,
the paper does not provide population projections for the deltas. This is an important
element in terms of preparing mitigation and adaptation strategies. Future
demographic research should therefore explicitly consider conducting robust
demographic projections based on a range of scenarios, including environmental
The results of the analysis presented in this study have important policy
implications. These delta regions will have to increasingly concentrate on addressing
the needs of growing elderly populations and ensuring provision of care. This can be a
challenging issue in developing countries where pension systems are often either
weak or non-existent. The changing population structures will also have implications
in terms of labour supply. Coupled with out migration, this will imply that specific
policies will have to be designed to tackle potential shifting from labour surplus to
labour shortages in certain sectors and geographical areas. Additionally,
environmental stressors, such as relative sea-level rise, could entail large population
displacements, including across national borders (Smajgl and Ward, 2013). With an
aging population, disaster preparedness programmes will have to be appropriately
Changes in occupational structure are also likely to be linked to internal
migration and resulting urban growth. Addressing potential labour shortages in the
farming sector is likely to be a challenge given that delta regions are food baskets for
many nations (Foufoula-Georgiou et al., 2013). Given the key role of demographic
and environmental issues for sustainability of tropical deltas, as well as their wider
interlinkages with other phenomena affecting sustainable development, such as public
health and good governance, it is critical to undertake thorough assessments of
specific population-environment dynamics on a case-by-case basis. Interlinked
population and environmental changes will have different consequences depending on
the delta. Policies related to the sustainable development of these three deltas and
future research on the deltaic systems should thus concentrate on further disentangling
population-environment associations, including through stakeholder engagement
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ESRC Centre for Population Change • Working Paper 74 • January 2016
ISSN 2042-4116
Improving our understanding of the key drivers and implications of population change
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... Social-ecological systems consist of biophysical (climate, geology, hydrology, ecology) and social factors that have coupled interactions. River deltas are some of the most heavily populated landforms on Earth Szabo et al., 2016), and understanding how these social-ecological systems evolve depends on sedimentation processes required for the delta to grow. These efforts are important because the stress of human occupation coupled with climate change has pushed many deltas to the brink of sustainability (Syvitski et al., 2009;Brondizio et al., 2016a). ...
... We consider deltas river-dominated when their dynamics and morphology are strongly linked to river processes at the coastline. River-dominated deltas are common (Nienhuis et al., 2020;Caldwell et al., 2019), and they often are among the larger and more densely populated deltas Szabo et al., 2016). We review studies that seek to understand the subaerial expression of river-dominated deltas, which is usually the result of basinward progradation as fluvial sediment accumulates nearshore and of the creation of distributary networks without progradation. ...
River deltas are a compelling target for numerical simulation because they contain seemingly organized patterns and shapes at a variety of scales. For instance, most river-dominated deltas, regardless of size, have triangular to semi-circular planform shapes, channel networks, and channel bifurcations. The common presence of these features among most deltas in the world (Caldwell et al., 2019; Nienhuis et al., 2020) suggests there are consistent underlying physical processes controlling delta form and behavior. In this review, we discuss how numerical modeling, and more specifically a type of modeling focused on the morphodynamic feedback, has helped explore some of these key physical processes over the last 15 years.
... Social-ecological systems consist of biophysical (climate, geology, hydrology, ecology) and social factors that have coupled interactions. River deltas are some of the most heavily populated landforms on Earth Szabo et al., 2016), and understanding how these social-ecological systems evolve depends on sedimentation processes required for the delta to grow. These efforts are important because the stress of human occupation coupled with climate change has pushed many deltas to the brink of sustainability (Syvitski et al., 2009;Brondizio et al., 2016a). ...
... We consider deltas river-dominated when their dynamics and morphology are strongly linked to river processes at the coastline. River-dominated deltas are common (Nienhuis et al., 2020;Caldwell et al., 2019), and they often are among the larger and more densely populated deltas Szabo et al., 2016). We review studies that seek to understand the subaerial expression of river-dominated deltas, which is usually the result of basinward progradation as fluvial sediment accumulates nearshore and of the creation of distributary networks without progradation. ...
... Social-ecological systems consist of biophysical (climate, geology, hydrology, ecology) and social factors that have coupled interactions. River deltas are some of the most heavily populated landforms on Earth Szabo et al., 2016), and understanding how these social-ecological systems evolve depends on sedimentation processes required for the delta to grow. These efforts are important because the stress of human occupation coupled with climate change has pushed many deltas to the brink of sustainability (Syvitski et al., 2009;Brondizio et al., 2016a). ...
... We consider deltas river-dominated when their dynamics and morphology are strongly linked to river processes at the coastline. River-dominated deltas are common (Nienhuis et al., 2020;Caldwell et al., 2019), and they often are among the larger and more densely populated deltas Szabo et al., 2016). We review studies that seek to understand the subaerial expression of river-dominated deltas, which is usually the result of basinward progradation as fluvial sediment accumulates nearshore and of the creation of distributary networks without progradation. ...
River-dominated deltas on Earth are composed of diverse shapes and patterns, ranging from small-scale bifurcations that create channel networks to large-scale deltaic lobes that build deltaic plains. Morphodynamic feedbacks among fluid flow, sediment transport, and bed elevation change are ultimately responsible for creating these shapes and patterns, and understanding how this morphodynamic feedback constructs deltaic landscapes will contribute to developing sustainable solutions for threatened deltaic environments. In this review, we explore what morphodynamic modeling approaches are commonly used to understand how deltas grow. We also explore what the community has learned by using these models and highlight key knowledge gaps to inspire new models and new questions about river-dominated deltas.
... 3 As estimativas disponíveis sinalizam uma inconteste queda, com uma TFT em 2015 próxima de 1,5, menor do que a média de Rondônia (1,8) (BARROS et al., 2021). Essa tendência é a verificada em outras regiões amazônicas, como, por exemplo, no delta do Rio Amazonas (SZABO et al., 2016). ...
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Analisam-se as estratégias reprodutivas de duas coortes de mulheres que viveram seu período reprodutivo em diferentes estágios de evolução de uma região de fronteira agrícola na Amazônia brasileira. Entende-se por estratégia reprodutiva a adoção de determinado comportamento reprodutivo e contraceptivo segundo as possibilidades e adversidades oferecidas no contexto da fronteira. O objetivo é avaliar as mudanças nessa estratégia ao longo do processo de desenvolvimento desse tipo de fronteira. As distintas condições socioeconômicas que os estágios de desenvolvimento da fronteira oferecem tornariam as estratégias reprodutivas diferenciadas, influenciando as decisões das mulheres que viveram seu período reprodutivo nas fases iniciais ou nas mais avançadas da fronteira. Foram realizadas entrevistas semiestruturadas em Machadinho d’Oeste, Rondônia, com 60 mulheres. Os resultados apontam que, contrariamente ao referido na literatura, não haveria uma relação direta entre uso da terra e o número de filhos. O comportamento reprodutivo de cada coorte se relaciona mais à infraestrutura de serviços de saúde sexual e reprodutiva e às condições socioeconômicas individuais e da fronteira. Para ambos os grupos, porém, a união e a maternidade são precoces e existem elevada falha contraceptiva e alta proporção de laqueadura.
... Importantly, many of the environmental, and socioeconomic and historical occupation conditions reflect significant differences between the three districts (Cardoso, 2007;Lima et al., 2011). However, the overall loss of vegetation coverage in these districts follows some common patterns for cities in the Amazon region showing a tendency of natural environments degradation with the loss of natural cover (Perz, 2000;Guedes et al., 2011;Szabo et al., 2016). a. Conflicts derived from legality in tenure and ownership of land. ...
... Cities in the region are predominantly small, with 70 % of them having a population of less than 50,000 inhabitants. However, the regional urban population is significantly concentrated (56 %) in the two state capitals, Belém (Pará) and Macapá (Amapá) (Szabo et al. 2016; Costa and Brondizio 2011). Most of the regional population has been living in urban areas since the 1960. ...
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At the nexus of watersheds, land, coastal areas, oceans, and human settlements, river delta regions pose specific challenges to environmental governance and sustainability. Using the Amazon Estuary-Delta region (AD) as our focus, we reflect on the challenges created by the high degree of functional interdependencies shaping social–ecological dynamics of delta regions. The article introduces the initial design of a conceptual framework to analyze delta regions as coupled social–ecological systems (SES). The first part of the framework is used to define a delta SES according to a problem and/or collective action dilemma. Five components can be used to define a delta SES: social–economic systems, governance systems, ecosystems-resource systems, topographic-hydrological systems, and oceanic-climate systems. These components are used in association with six types of telecoupling conditions: socio-demographic, economic, governance, ecological, material, and climatic-hydrological. The second part of the framework presents a strategy for the analysis of collective action problems in delta regions, from sub-delta/local to delta to basin levels. This framework is intended to support both case studies and comparative analysis. The article provides illustrative applications of the framework to the AD. First, we apply the framework to define and characterize the AD as coupled SES. We then utilize the framework to diagnose an example of collective action problem related to the impacts of urban growth, and urban and industrial pollution on small-scale fishing resources. We argue that the functional interdependencies characteristic of delta regions require new approaches to understand, diagnose, and evaluate the current and future impacts of social–ecological changes and potential solutions to the sustainability dilemmas of delta regions.
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Climate change is intensifying tropical cyclones, accelerating sea-level rise, and increasing coastal flooding. River deltas are especially vulnerable to flooding because of their low elevations and densely populated cities. Yet, we do not know how many people live on deltas and their exposure to flooding. Using a new global dataset, we show that 339 million people lived on river deltas in 2017 and 89% of those people live in the same latitudinal zone as most tropical cyclone activity. We calculate that 41% (31 million) of the global population exposed to tropical cyclone flooding live on deltas, with 92% (28 million) in developing or least developed economies. Furthermore, 80% (25 million) live on sediment-starved deltas, which cannot naturally mitigate flooding through sediment deposition. Given that coastal flooding will only worsen, we must reframe this problem as one that will disproportionately impact people on river deltas, particularly in developing and least-developed economies.
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Climate change is intensifying tropical cyclones, accelerating sea-level rise, and increasing coastal flooding. Coastal flooding will not affect all environments equally, and river deltas are especially vulnerable because of their low elevations, densely populated cities, and river channels that propagate coastal floods inland. Yet, we do not know how many people live on deltas and their exposure to flooding. Using a new global dataset of 2,174 river delta locations and areas, we show that in 2017 there were 339 million people living on river deltas with 329 million (or 97%) living in developing and least-developed economies. We show that geographically, 88% of people on river deltas live in the same zone as most tropical cyclone activity. Of all the people exposed to tropical cyclone flooding, our analysis suggests 41% (or 31 million) live on deltas. Of these, 92% (or 28 million) live in developing or least developed economies, where lacking infrastructure for hazard mitigation increases their vulnerability. Furthermore, 80% (or 25 million) live on sediment-starved deltas that are unable to naturally mitigate flooding through sediment deposition. The 2019 IPCC special report makes it clear that coastal flooding will increase, and it is essential that we reframe the concept of coastal flooding as a problem that will disproportionately impact people on river deltas, particularly in developing and least-developed countries.
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In the past 40 years, Brazil has experienced rapid fertility decline, where the number of children per woman (i.e., total fertility rate) has dropped sharply from 6.0 in the 1960s to 2.3 in the late 1990s. What makes Brazil's fertility decline particularly interesting is its strong reliance on a nonreversible method of contraception: tubal ligation, here referred to as female sterilization. As recently as 1996, the country led the world in recorded rates of female sterilization, This practice is so pervasive and dominant that among some Brazilian scholars it has come to be called the surgical transition rather than the fertility transition. In this paper, we discuss the prevalence of female sterilization and other contraceptive methods among rural women of the Lower Amazon. The use of reversible (e.g., the pill, condoms) and irreversible (sterilization) methods is analyzed in terms of women's birth cohorts and in terms of their individual characteristics. We argue that to understand contraceptive choices we need to consider the social and cultural context, particularly the availability of local health services, the influence of doctors and politicians, as well as women's own goals for themselves and their children.
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In much of the Amazon Basin, approximately 70% of the population lives in urban areas and urbanward migration continues. Based on data collected over more than a decade in two long-settled regions of Amazonia, we find that rural-urban migration in the region is an extended and complex process. Like recent rural-urban migrants worldwide, Amazonian migrants, although they may be counted as urban residents, are often not absent from rural areas but remain members of multi-sited households and continue to participate in rural-urban networks and in rural land-use decisions. Our research indicates that, despite their general poverty, these migrants have affected urban markets for both food and construction materials. We present two cases: that of açaí palm fruit in the estuary of the Amazon and of cheap construction timbers in the Peruvian Amazon. We find that many new Amazonian rural-urban migrants have maintained some important rural patterns of both consumption and knowledge. Through their consumer behavior, they are affecting the areal extent of forests; in the two floodplain regions discussed, tree cover is increasing. We also find changes in forest composition, reflecting the persistence of rural consumption patterns in cities resulting in increased demand for and production of açaí and cheap timber species.
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Coastal Bangladesh experiences significant poverty and hazards today and is highly vulnerable to climate and environmental change over the coming decades. Coastal stakeholders are demanding information to assist in the decision making processes, including simulation models to explore how different interventions, under different plausible future socio-economic and environmental scenarios, could alleviate environmental risks and promote development. Many existing simulation models neglect the complex interdependencies between the socio-economic and environmental system of coastal Bangladesh. Here an integrated approach has been proposed to develop a simulation model to support agriculture and poverty-based analysis and decision-making in coastal Bangladesh. In particular, we show how a simulation model of farmer's livelihoods at the household level can be achieved. An extended version of the FAO's CROPWAT agriculture model has been integrated with a downscaled regional demography model to simulate net agriculture profit. This is used together with a household income-expenses balance and a loans logical tree to simulate the evolution of food security indicators and poverty levels. Modelling identifies salinity and temperature stress as limiting factors to crop productivity and fertilisation due to atmospheric carbon dioxide concentrations as a reinforcing factor. The crop simulation results compare well with expected outcomes but also reveal some unexpected behaviours. For example, under current model assumptions, temperature is more important than salinity for crop production. The agriculture-based livelihood and poverty simulations highlight the critical significance of debt through informal and formal loans set at such levels as to persistently undermine the well-being of agriculture-dependent households. Simulations also indicate that progressive approaches to agriculture (i.e. diversification) might not provide the clear economic benefit from the perspective of pricing due to greater susceptibility to climate vagaries. The livelihood and poverty results highlight the importance of the holistic consideration of the human-nature system and the careful selection of poverty indicators. Although the simulation model at this stage contains the minimum elements required to simulate the complexity of farmer livelihood interactions in coastal Bangladesh, the crop and socio-economic findings compare well with expected behaviours. The presented integrated model is the first step to develop a holistic, transferable analytic method and tool for coastal Bangladesh. This journal is
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Coastal flooding due to storm surge and high tides is a serious risk for inhabitants of the Ganges-Brahmaputra-Meghna (GBM) delta, as much of the land is close to sea level. Climate change could lead to large areas of land being subject to increased flooding, salinization and ultimate abandonment in both West Bengal, India, and Bangladesh. IPCC 5th assessment modelling of sea level rise and estimates of subsidence rates from the EU IMPACT2C project suggest that sea level in the GBM delta region may rise by 0.63 to 0.88 m by 2090, with some studies suggesting this could be up to 0.5 m higher if potential substantial melting of the West Antarctic ice sheet is included. These sea level rise scenarios lead to increased frequency of high water coastal events. Any effect of climate change on the frequency and severity of storms can also have an effect on extreme sea levels. A shelf-sea model of the Bay of Bengal has been used to investigate how the combined effect of sea level rise and changes in other environmental conditions under climate change may alter the frequency of extreme sea level events for the period 1971 to 2099. The model was forced using atmospheric and oceanic boundary conditions derived from climate model projections and the future scenario increase in sea level was applied at its ocean boundary. The model results show an increased likelihood of extreme sea level events through the 21st century, with the frequency of events increasing greatly in the second half of the century: water levels that occurred at decadal time intervals under present-day model conditions occurred in most years by the middle of the 21st century and 3-15 times per year by 2100. The heights of the most extreme events tend to increase more in the first half of the century than the second. The modelled scenarios provide a case study of how sea level rise and other effects of climate change may combine to produce a greatly increased threat to life and property in the GBM delta by the end of this century.
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The flood is a well-known phenomenon in the Vietnamese Mekong River Delta (MRD). Although people have experienced the impact of floods for years, some adapt well, but others are vulnerable to floods. Resilience to floods is a useful concept to study the capacity of rural households to cope with, adapt to, and benefit from floods. Knowledge of the resilience of households to floods can help disaster risk managers to design policies for living with floods. Most researchers attempt to define the concept of resilience; very little research operationalizes it in the real context of "living with floods". We employ a subjective well-being approach to measure households' resilience to floods. Items that related to households' capacity to cope with, adapt to, and benefit from floods were developed using both a five-point Likert scale and dichotomous responses. A factor analysis using a standardized form of data was employed to identify underlying factors that explain different properties of households' resilience to floods. Three properties of households' resilience to floods were found: (1) households' confidence in securing food, income, health, and evacuation during floods and recovery after floods; (2) households' confidence in securing their homes not being affected by a large flood event such as the 2000 flood; (3) households' interests in learning and practicing new flood-based farming practices that are fully adapted to floods for improving household income during the flood season. The findings assist in designing adaptive measures to cope with future flooding in the MRD.
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Relative sea/land level changes are fundamental to people living in deltas. Net subsidence is complex and attributed to tectonics, compaction, sedimentation and anthropogenic causes. It can have severe impacts and needs to be quantified and where possible (subsidence due to anthropogenic causes) avoided. For the highly populated Ganges-Brahmaputra-Meghna delta, a large range of net subsidence rates are described in the literature, yet the reasons behind this wide range of values are poorly understood. This paper documents and analyses rates of subsidence (for publications until 2014) and relates these findings to human influences (development). 205 point measurements of net subsidence were found, reported in 24 studies. Reported measurements were often repetitive in multiple journals, with some lacking detail as to precise location, cause and method, questioning reliability of the rate of subsidence. Rates differed by locality, methodology and period of measurement. Ten different measurement methods were recorded, with radio-carbon dating being the most common. Temporal and spatially, rates varied between -1.1mm/yr (i.e. uplift) and 43.8mm/yr. The overall mean reported rate was 5.6mm/yr, and the overall median 2.9mm/yr, with 7.3mm/yr representing one standard deviation. These rates were reduced if inaccurate or vague records were omitted. The highest rates were recorded in the Sylhet Plateau, Dhaka and Kolkata. Highest rates were recorded in the last 1,000 years, where the mean increased to 8.8mm/yr and a standard deviation of 7.5mm/yr. This could be partly due to shorter-term measurement records, or anthropogenic influence as multiple high rates are often found in urban settings. Continued development may cause rates to locally increase (e.g. due to groundwater abstraction and/or drainage). Improved monitoring is required over a wider area, to determine long-term trends, particularly as short-term records are highly variable. Focus in regions where wide spread development is occurring or is expected would be advantageous.
Tropical storms, such as cyclones, hurricanes and typhoons, present major threats to coastal communities. Around two million people worldwide have died and millions have been injured over the past two centuries as a result of tropical storms. Bangladesh is especially vulnerable to tropical cyclones, with around 718 000 deaths from them in the past 50 years. However, cyclone-related mortality in Bangladesh has declined by more than 100-fold over the past 40 years, from 500 000 deaths in 1970 to 4234 in 2007. The main factors responsible for these reduced fatalities and injuries are improved defensive measures, including early warning systems, cyclone shelters, evacuation plans, coastal embankments, reforestation schemes and increased awareness and communication. Although warning systems have been improved, evacuation before a cyclone remains a challenge, with major problems caused by illiteracy, lack of awareness and poor communication. Despite the potential risks of climate change and tropical storms, little empirical knowledge exists on how to develop effective strategies to reduce or mitigate the effects of cyclones. This paper summarizes the most recent data and outlines the strategy adopted in Bangladesh. It offers guidance on how similar strategies can be adopted by other countries vulnerable to tropical storms. Further research is needed to enable countries to limit the risks that cyclones present to public health.