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Transitioning from the Millennium Development Goals (MDG) to the Sustainable Development Goals (SDG) is a big challenge, particularly for SDG 6.1, as the effective delivery of drinking water services drops due to more stringent indicators, especially for water quality constraints. Salinity in groundwater has received less attention compared to arsenic and E. Coli in the MDG era, while its presence and widespread variability has considerable implications in larger coastal areas for achieving SDG 6.1 targets. This article analyzes drinking water security in southwest coastal Bangladesh, through an in-depth field investigation. It reveals that the exponential growth of groundwater-based technologies, such as tube wells, does not necessarily indicate the actual safe drinking water coverage in coastal areas, due to complex hydrogeology with the high spatial variability of groundwater salinity risks. The spatial variability of hydrogeologic constraints and groundwater salinity risks also reinforces concerns of access, reliability, and affordability with different water supply technologies. National estimates can be misleading as the presence of salinity substantially lowers the effective drinking water coverage. Infrastructural investments for drinking water supply need to consider a sound knowledge of hydrogeologic heterogeneity, and the monitoring of water quality, if the SDG 6.1 targets are to be met.

Increasing flood risk, salinization and waterlogging threaten the lives and livelihoods of more than 35 million people in Bangladesh’s coastal zone. While planning models have long been used to inform investments in water infrastructure, they frequently overlook interacting risks, impacts on the poor and local context. We address this gap by developing and applying a stochastic-optimization model to simulate the impact of flood embankment investments on the distribution of agricultural incomes across income groups for six diverse polders (embanked areas) in coastal Bangladesh. Results show that increasing salinity and waterlogging negate the benefits of embankment rehabilitation in improving agricultural production while improved drainage can alleviate these impacts. Outcomes vary across income groups, with risks of crop loss being greatest for the poor. We discuss the need for planning models to consider the interacting benefits and risks of infrastructure investments within a local political economy to better inform coastal adaptation decisions.

We investigated the merits of performing multi-scale flood simulations with nested two-dimensional flood simulation models for flood risk management applications over an extended period with infilt...

The co-creation of knowledge through a process of mutual learning between scientists and societal actors is an important avenue to advance science and resolve complex problems in society. While the value and principles for such transdisciplinary water research have been well established, the power and empowerment dimensions continue to pose a challenge, even more so in international processes that bring together participants from the Global North and Global South. We build on earlier research to combine known phases, activities, and principles for transdisciplinary water research with a negotiated approach to stakeholder empowerment. Combining these elements, we unpack the power and empowerment dimension in transdisciplinary research for peri-urban groundwater management in the Ganges Delta. Our case experiences show that a negotiated approach offers a useful and needed complement to existing transdisciplinary guidelines. Based on the results, we identify responses to the power and empowerment challenges, which add to existing strategies for transdisciplinary research. A resulting overarching recommendation is to engage with power and politics more explicitly and to do so already from the inception of transdisciplinary activities as a key input for problem framing and research agenda setting.

Groundwater is used intensively in Asian mega-deltas yet the processes by which groundwater is replenished in these deltaic systems remain inadequately understood. Drawing insight from hourly monitoring of groundwater levels and rainfall in two contrasting settings, comprising permeable surficial deposits of Holocene age and Plio-Pleistocene terrace deposits, together with longer-term, lower-frequency records of groundwater levels, river stage, and rainfall from the Bengal Basin, conceptual models of recharge processes in these two depositional environments are developed. The representivity of these conceptual models across the Bengal Basin in Bangladesh is explored by way of statistical cluster analysis of groundwater-level time series data. Observational records reveal that both diffuse and focused recharge processes occur in Holocene deposits, whereas recharge in Plio-Pleistocene deposits is dominated by indirect leakage from river channels where incision has enabled a direct hydraulic connection between river channels and the Plio-Pleistocene aquifer underlying surficial clays. Seasonal cycles of recharge and discharge including the onset of dry-season groundwater-fed irrigation are well characterised by compiled observational records. Groundwater depletion, evident from declining groundwater levels with a diminished seasonality, is pronounced in Plio-Pleistocene environments where direct recharge is inhibited by the surficial clays. In contrast, intensive shallow groundwater abstraction in Holocene environments can enhance direct and indirect recharge via a more permeable surface geology. The vital contributions of indirect recharge of shallow groundwater identified in both depositional settings in the Bengal Basin highlight the critical limitation of using models that exclude this process in the estimation of groundwater recharge in Asian mega-deltas.

Achieving water security requires reconciling multiple objectives while prioritizing scarce resources for the provision of safe drinking water supplies. We examine decision-making to invest in drinking water infrastructure in coastal Bangladesh where increasing saline intrusion in aquifers intersects with high levels of poverty for the 20 million people living in the coastal region. Multi-objective optimization is used to explore the trade-offs between two public policy goals: (a) maximizing overall access to improved water supplies (the greater good) and (b) maximizing access for the population with the lowest welfare (the greater need). To elucidate this trade-off, we make use of groundwater salinity measurements, an extensive household survey and an audit of drinking water infrastructure in 1 out of Bangladesh's 139 polders, which is home to nearly 60,000 people. We quantify the costs of a variety of drinking water supply options including deep tube wells, desalination plants, and piped systems. The recommended solutions are sequences of investments in water supply assets that are optimized to specified locations within the polder. The method is potentially scalable and transferrable to inform investments to achieve the Sustainable Development Goal (Target 6.1) of universal access to safe and affordable drinking water., Water Resources Research, 57 (8), ISSN:0043-1397, ISSN:1944-7973

This paper uses multimedia to showcase the narratives and lived experiences of those who live and work in tropical Asian mega‐deltas, and as such is the first journal article of its kind in the field of Regional Geography. Using videos, photography and audio this paper describes the characteristics of ponds and their place in the intrinsically connected human‐environmental fabric of these delta regions. The aim is to bring to life descriptive inventories and provide greater weight in support of our conclusion that tropical Asian mega‐delta ponds are important and threatened systems. River deltas comprise just 1% of land cover worldwide but support the livelihoods of more than 500 million people. Delta research has historically focused on the major river channels and the socio‐ecological role of ponds has been overlooked despite their large number and surface area. Ponds are intrinsically linked to daily life (potable water, sanitation, bathing, washing), industry (aquaculture, agriculture) and the natural‐cultural heritage (religion, folklore) of deltas. In contrast to the larger river channels, ponds are likely to be significant stores and processors of nutrients, including carbon, and pollutants at annual to decadal scales, on account of their heavy anthropogenic use and smaller individual sizes. Consequently, they are severely polluted water sources and pose significant public health risks. In this review, we use case studies from three Asian mega‐deltas (the Red River Delta and the Mekong River Delta, Vietnam, and the Ganges‐Brahmaputra‐Meghna Delta, India and Bangladesh) to highlight the importance of Asian mega‐delta ponds as important socio‐ecological systems in their own right. We discuss future environmental challenges, knowledge gaps on the ecological function and biodiversity of these habitats, management and policy practices, and the capacity of ponds to achieve the UN Sustainable Development Goals.

Groundwater resources in deltaic regions are vulnerable to contamination by saline seawater, posing significant crisis for drinking water. Current policy and practice of building water supply infrastructure, without adequate hydrogeological analysis and institutional coordination are failing to provide basic drinking water services for millions of poor people in such difficult hydrogeological contexts. We apply a social-ecological systems approach to examine interdisciplinary data from hydrogeological mapping, a water infrastructure audit, 2103 household surveys, focus group discussions and interviews to evaluate the risks to drinking water security in one of 139 polders in coastal Bangladesh. We find that increasing access through public tubewells is common but insufficient to reduce drinking water risks. In response, there has been a four-fold growth in private investments in shallow tubewells with new technologies and entrepreneurial models to mitigate groundwater salinity. Despite these interventions, poor households in water-stressed environments face significant trade-offs in drinking water quality, accessibility and affordability. We argue that institutional coordination and hydrogeological monitoring at a systems level is necessary to mitigate socio-ecological risks for more equitable and efficient outcomes.

Deltas occupy only 1% of global land surface area, but contain 7% of the global human population (ca. 500 million). The influence of changing and interacting climates, demography, economy, land use and coastal/catchment management on deltaic social-ecological systems is complex and little understood. We apply a new and innovative integrated assessment model: The Delta Dynamic Integrated Emulator Model (ΔDIEM) to coastal Bangladesh to explore a range of plausible future scenarios and quantify the sensitivities of selected environmental and socio-economic outcomes to key external and internal drivers. ΔDIEM is a tightly coupled integrated assessment platform considering climate and environmental change, demographic changes, economic changes, household decision making and governance, and designed to support the delta planning in Bangladesh. ΔDIEM allows the testing of a large number of water-based structural and policy interventions within a robust scenario framework, as well as quantify different development trajectories and their trade-offs. In this sensitivity analysis, we quantified the impact of (i) climate (precipitation, temperature and runoff), (ii) relative sea-level rise, (iii) cyclone frequency, (iv) embankment maintenance, (v) population size, (vi) economic changes at household level such as selling price of crops, cost of food, etc., (vii) land cover, and (viii) farming practices on trajectories of inundated area, soil salinity, rice productivity, poverty, income inequality and GDP/capita, assuming two contrasting scenarios in a more Positive and a more Negative World. Trajectories of these plausible futures showed a clear separation and the long-term trends are greatly influenced by the combinations of scenario assumptions. Our systemic results indicate a diverse potential set of futures for coastal Bangladesh, where good governance and adaptation could effectively mitigate the threat of sea-level rise-induced catastrophic inundation and other adverse impacts of the changing climate. However, societal inequality requires special attention otherwise climate-sensitive population groups may be left behind.

Policy development and management of deltas in the Anthropocene involves the consideration of trade-offs and the balancing of positive and negative consequences for delta functions and the societies that rely on them. This assessment outlines policy-driven and spatial trade-offs that dominate the landscape of choice. It highlights examples of such trade-offs using plausible delta futures and the governance choices associated with them. The analysis is based on modelling broad-scale processes and individual adaptive actions. It highlights how policy choices to maximise economic growth can, for example, have unforeseen consequences such as diminished well-being for some populations. Hence the chapter concludes that trade-offs are a crucial governance challenge for future sustainability of deltas.

Deltas are experiencing profound demographic, economic and land use changes and human-induced catchment and climate change. Bangladesh exemplifies these difficulties through multiple climate risks including subsidence/sea-level rise, temperature rise, and changing precipitation patterns, as well as changing management of the Ganges and Brahmaputra catchments. There is a growing population and economy driving numerous more local changes, while dense rural population and poverty remain significant. Identifying appropriate policy and planning responses is extremely difficult in these circumstances. This paper adopts a participatory scenario development process incorporating both socio-economic and biophysical elements across multiple scales and sectors as part of an integrated assessment of ecosystem services and livelihoods in coastal Bangladesh. Rather than simply downscale global perspectives, the analysis was driven by a large and diverse stakeholder group who met with the researchers over four years as the assessment was designed, implemented and applied. There were four main stages: (A) establish meta-framework for the analysis; (B) develop qualitative scenarios of key trends; (C) translate these scenarios into quantitative form for the integrated assessment model analysis; and (D) a review of the model results, which raises new stakeholder insights (e.g., preferred adaptation and policy responses) and questions. Step D can be repeated leading to an iterative learning loop cycle, and the process can potentially be ongoing. The strong and structured process of stakeholder engagement gave strong local ownership of the scenarios and the wider process. This process can be generalised for widespread application across socio-ecological systems following the same four-stage approach. It demands sustained engagement with stakeholders and hence needs to be linked to a long-term research process. However, it facilitates a more credible foundation for planning especially where there are multiple interacting factors.

The Ganges-Brahmaputra-Meghna (GBM) Delta and its catchment area are shared between five countries which means that the delta is strongly influenced by neighbouring country’s water and sediment management decisions in addition to climatic, environmental and internal management. Delta administration is also shared between Bangladesh and India, including the unique Sundarbans mangrove forest. An overview of delta-building and socio-ecological processes from Holocene to Anthropocene are outlined providing a background for current issues. These include discussion on emerging opportunities and challenges, growth of settlements/land use, vulnerability mapping and options for adaptation including migration. Preliminary social vulnerability maps for the Joint GBM Delta are presented. These could facilitate the engagement of policymakers of all countries to create opportunities for co-learning to resolve delta level issues.

Coastal people, especially those living within deltaic areas, encounter major climatic concerns which affect their livelihoods. To cope with this problem, different types of planned adaptation strategies have been implemented guided by laws, policies and programs. However, these guiding documents sometimes fall short of addressing the needs of climate-affected people, especially in natural resource-dependent societies in Asia and Africa. Based on this premise, this paper sought to evaluate the effectiveness of existing policy documents which affect the lives of people living in one large delta (Ganges-Brahmaputra-Meghna in Bangladesh), two medium-sized deltas (Indian Bengal delta&mdash, part of the Ganges-Brahmaputra-Meghna and Mahanadi in India), and a small-sized delta (Volta in Ghana). The study followed a mixed methods research design, which included desktop analyses of policies, laws and programs, a questionnaire survey conducted among individuals who played various roles in the policy and legal development processes at national and local levels and focus group discussions at the community level in the three countries. National laws, policies and programs were assessed in the context of climate change adaptation through three lenses: human rights, natural resource management and disaster response. Findings of this paper reveal that the existing documents have some strengths to promote adaptation, although they have some major limitations that cause concerns among the delta communities.

The coastal areas of the Ganges-Brahmaputra-Meghna delta are acknowledged hotspots of environmental and social concerns. This reflects a large, mainly rural population of 56.7 million, which is exposed to a range of natural hazards exacerbated by climate change, sea-level rise and subsidence. There are high levels of poverty and limited social well-being, including poor access to education, health, drinking water, and sanitation facilities. A spatial assessment of social vulnerability can indicate which communities are more susceptible to environmental hazards, while a temporal assessment may indicate how such vulnerability is changing due to development and other drivers. This study provides the first analysis of social vulnerability across the entire coastal delta within Bangladesh and India. It uses consistent and common secondary data at the sub-district level for two time periods: 2001 and 2011. These are used to construct a socio-economic vulnerability index across the region using Principal Component Analysis. Three main conclusions emerge. Firstly, there is a cross-shore social vulnerability gradient across the whole delta, with more vulnerable people living near the coast. Here, the benefits of access to marine fisheries are not apparent. Secondly, non-agricultural development and economic expansion have reduced the vulnerability significantly, showing its benefits. Lastly, despite general positive development trends, shocks due to major cyclone landfall appear to have enhanced vulnerability in the impacted areas. Further comprehensive analysis across the whole delta is recommended to improve our understanding of the common threats and possible solutions.

A flexible meta-model, the Delta Dynamic Integrated Emulator Model (ΔDIEM), is developed to capture the socio-biophysical system of coastal Bangladesh as simply and efficiently as possible. Operating at the local scale, calculations occur efficiently using a variety of methods, including linear statistical emulators, which capture the behaviour of more complex models, internal process-based models and statistical associations. All components are tightly coupled, tested and validated, and their behaviour is explored with sensitivity tests. Using input data, the integrated model approximates the spatial and temporal change in ecosystem services and a number of livelihood, well-being, poverty and health indicators of archetypal households. Through the use of climate, socio-economic and governance scenarios plausible trajectories and futures of coastal Bangladesh can be explored.

The Sustainable Development Goals (SDGs) are offered as a comprehensive strategy to guide and encourage sustainable development at multiple scales both nationally and internationally. Furthermore, through the development of indicators associated with each goal and sub-goal, the SDGs support the notion of monitoring, evaluation and adaptive management, underpinned by the aspirations of social justice, equity and transparency. As such, the ethical intention of the SDGs is well founded. However, possible conflicts and trade-offs between individual SDGs have received little attention. For example, SDGs relating to poverty (SDG 1), inequality (SDG 10), food security (SDG2), economic development (SDG 8) and life in water and on land (SDGs 14 and 15), are potentially competing in many circumstances. In a social-ecological context, policy support and formulation are increasingly adopting systems approaches, which analyse the complex interactions of system elements. Adopting such an approach in this work, the above SDGs are analysed for coastal Bangladesh. This demonstrates multiple potential trade-offs between the SDGs, including agricultural farming approaches in the light of poverty reduction, and between economic growth and environmental integrity as well as equity. To develop coherent and policy relevant socio-ecological strategies, appropriate decision frameworks need to be co-developed across the range of stakeholders and decision-makers. Integrated models have great potential to support such a process.

The IPCC fifth assessment report envisions risk of climate-related impacts as an outcome of the interaction of climate-related hazards with the vulnerability and the exposure of human and natural systems. This approach relies heavily on human perception, via expert opinions. As experts decide appropriate placement of an indicator in any of the exposure, sensitivity or adaptive capacity domains, several risk maps can potentially be created for the same study area. There is thus some degree of uncertainty in selecting the most appropriate and representative risk map from the several alternatives created by IPCC methods. On the other hand, Fuzzy Synthetic Evaluation (FSE) method, when used to assess risk, can handle this uncertainty much better, as there is no need to distribute indicators among different domains. In FSE, a specific indicator can either increase (positive sign) or decrease (negative sign) a risk, following a simple binary logic. This does not require any expert opinion and thus is free from subjective perception. In this study, risk maps are generated and compared by applying FSE method and two IPCC methods, as outlined in the third and fifth assessments (TAR and AR5). A variant of AR5 risk map is created by interchanging one indicator from the exposure domain to the sensitivity domain. It is found that risk zones are created with statistically significant difference when different IPCC methods are applied. This makes it uncertain to judge a specific risk map by a specific IPCC method as a true risk map. This uncertainty does not exist in FSE method as there is only one risk map where indicators are placed with certainty by following a simple binary logic for a known hazard domain. Hence, this risk map may be considered as the true risk map for the given set of indicators.

Bangladesh is identified as an impact hotspot for sea-level rise in multiple studies. However, a range of other factors must be considered including catchment management, socio-economic development and governance quality, as well as delta plain biophysical processes. Taking an integrated assessment approach highlights that to 2050 future changes are more sensitive to human choice/policy intervention than climate change, ecosystem services diminish as a proportion of the economy with time, continuing historic trends and significant poverty persists for some households. Hence under favourable policy decisions, development could transform Bangladesh by 2050 making it less vulnerable to longer-term climate change and subsidence. Beyond 2050, the threats of climate change are much larger, requiring strategic adaptation responses and policy changes that must be initiated now.

Deltas are distinct in terms of the concentration of freshwater, nutrients and especially sediment inputs to a small concentrated area of the coastal zone, creating conditions ideal for fertile ecosystems, dense population and high economic activity. Ecosystem services within these areas can provide services significant in the maintenance of well-being for both rural and urban populations. There are significant feedbacks between environmental processes and social dynamics that drive the economic and well-being outcomes for current and future populations. This chapter reviews ecosystem services in deltas and summarises the state of knowledge in this field on how to manage delta ecosystems for the benefit of resident populations and wider society.

Seven distinct social-ecological systems are defined for the Bangladesh delta, based on analysis of the ways in which social systems differ according to the ecological system. These systems are rain-fed and irrigated agriculture, brackish and freshwater aquaculture, Charlands, coastal zones, and areas dependent on the Sundarbans mangrove forest. The social systems that inhibit or facilitate access to ecosystem services vary between social-ecological systems. The timing and nature of ecosystem services give rise to different livelihood opportunities, means of access to ecosystem services, and coping mechanisms. Thus, while the common challenge across all social-ecological systems is to design mechanisms by which the poorest populations retain value and benefits, these mechanisms will differ depending on the system.

The Ganges-Brahmaputra-Meghna delta in Bangladesh is one of the world’s most dynamic deltas and supports high population densities based on large provisioning ecosystem services. Analysing the future of these ecosystem services and associated human livelihoods represents a complex multi-scale, multi-disciplinary problem. A conceptual framework aims to identify mechanisms that link physical processes (including climate change) with ecosystem services and social outcomes providing a shared basis for other analysis, including the design of an integrated model. This also allows the characteristics of co-production of ecosystem services at the landscape scale and significant trade-offs between types of ecosystem services to be incorporated. Adopting a systems-based approach of this scale is challenging but essential to support the effective management of coastal Bangladesh.

Scenario development for integrated analysis focuses on adopting an interdisciplinary approach covering key elements of the biophysical environment as well as changes in livelihoods, education, economics and governance both locally and internationally. Most importantly, the development of these scenarios generates a dialogue across institutions, stakeholders and sectors, with the use of common data and agreement on shared qualitative and quantitative futures. The scenarios adopted combine three alternative future climates and three socio-economic development pathways. Quantification of these issues included estimation based on published data, expert knowledge and stakeholder engagement, particularly where data are most uncertain or unknown. This chapter demonstrates this approach for coastal Bangladesh.

Salinity intrusion in coastal Bangladesh has serious population health implications, which are yet to be clearly understood. The study was undertaken through the ‘Assessing Health, Livelihoods, Ecosystem Services and Poverty Alleviation in Populous Deltas’ project in coastal Bangladesh. Drinking water salinity and blood pressure measurements were carried out during the household survey campaign. The study explored association among Socio-Ecological Systems (SESs), drinking water salinity and blood pressure. High blood pressure (prehypertension and hypertension) was found significantly associated with drinking water salinity. People exposed to slightly saline (1000–2000 mg/l) and moderately saline (≥2000 mg/l) concentration drinking water had respectively 17% (p < 0.1) and 42% (p < 0.05) higher chance of being hypertensive than those who consumed fresh water ( Localized increase in soil and groundwater salinity was predicted over the study area. Shallow aquifer salinity increase was projected based on modelled output of soil salinity. Rather than uniform increase, there were localized extreme values. Deep aquifer salinity was also predicted to exhibit increasing trend over the period. Study findings and recommendations are suggested for immediate and planned intervention.

This book answers key questions about environment, people and their shared future in deltas. It develops a systematic and holistic approach for policy-orientated analysis for the future of these regions. It does so by focusing on ecosystem services in the world’s largest, most populous and most iconic delta region, that of the Ganges-Brahmaputra delta in Bangladesh. The book covers the conceptual basis, research approaches and challenges, while also providing a methodology for integration across multiple disciplines, offering a potential prototype for assessments of deltas worldwide. Ecosystem Services for Well-Being in Deltas analyses changing ecosystem services in deltas; the health and well-being of people reliant on them; the continued central role of agriculture and fishing; and the implications of aquaculture in such environments.The analysis is brought together in an integrated and accessible way to examine the future of the Ganges Brahmaputra delta based on a near decade of research by a team of the world’s leading scientists on deltas and their human and environmental dimensions. This book is essential reading for students and academics within the fields of Environmental Geography, Sustainable Development and Environmental Policy focused on solving the world’s most critical challenges of balancing humans with their environments.

Multiple criteria decision making (MCDM) is a process of evaluating alternatives against relevant decision making criteria. Several methods are available to facilitate the evaluation steps. This paper deals with a rural water supply problem in the coastal areas of Bangladesh. Three different MCDM methods – weighted summation, analytical hierarchy process, and novel approach to imprecise assessment and decision environments – were used to evaluate the suitable water supply alternative. The ranking of alternatives obtained from these MCDM techniques produced similar results. Among five water supply alternatives evaluated, rainwater harvesting systems and deep tube wells scored first and second, respectively, for all three evaluation methods. In addition, sensitivity analyses were carried out for the MCDM techniques and these results did not show drastic variations either. This finding implies that while selection of MCDM technique is important, when evaluating similar problems more emphasis should be given to defining the problem comprehensively and thus selecting the relevant criteria and priorities to factor into the decision problem.

Water-related risks impact development opportunities and can trap communities in a downward spiral of economic decline. In this article, the dynamic relationship between water-related risks and economic outcomes for an embanked area in coastal Bangladesh is conceptualized. The interaction between flood events, salinity, deteriorating and poorly maintained water infrastructure, agricultural production and income is modelled. The model is used to test the effect of improvements in the reliability, operation and maintenance of the water infrastructure on agricultural incomes and assets. Results indicate that interventions can have non-marginal impacts on indicators of welfare, switching the system dynamic from a poverty trap into one of growth.

Understanding the dynamics of salt movement in the soil is a prerequisite for devising 23 appropriate management strategies for land productivity of coastal regions, especially low lying 24 delta regions which support many millions of farmers around the world. In this research, we 25 develop a novel holistic approach to simulate soil salinization comprising an emulator-based soil 26 salt and water balance calculated at daily time steps. The method is demonstrated for the 27 agriculture areas of Coastal Bangladesh. This shows that we can reproduce the dynamics of soil 28 salinity under multiple land uses, including rice crops, combined shrimp and rice farming, as 29 well as non-rice crops. The model also reproduced well the observed spatial soil salinity for the 30 year 2009. Using this approach, we have projected the soil salinity for three different climate 31 ensembles, including relative sea-level rise for the period 2041-2050. The results indicate an 32 increase in soil salinity in 21-44% of the simulated area. This can potentially cause significant 33 crop yield reductions, especially for vegetables and local rice varieties. The modelling approach 34 will enable planners and land use managers to investigate future trajectories of salinity impacts 35 on crop production, considering expected changes in relative sea level, groundwater pumping 36 and water quality in the rivers and estuary, and management responses to augment freshwater 37 supplies.

Availability of safe drinking water is considered a key challenge in the coastal region of Bangladesh. High concentrations of salinity, iron and arsenic, and the unavailability of suitable aquifers, have deterred the exploitation of groundwater resources. In addition the cyclonic storm surge is a major threat to this system. Cyclones accompanied by storm surges in the coastal area cause significant deterioration of drinking water supply and sanitation. Water professionals have launched some initiatives to promote small-scale, alternative safe water sources (e.g. rainwater harvesting, pond sand filters and piped water techniques) to provide sustainable solutions to the problem. However, a systematic evaluation of the alternatives that considers social, technical and economic criteria has not been carried out so far. The present study is an attempt to evaluate the alternative options for drinking water supply in a cyclone-prone area. The authors conducted a multi-criteria analysis and reached the conclusion that rainwater harvesting is the most suitable option for the area. Moreover, the final result was shared with the users to obtain their feedback to ensure sustainability of the water source.

Deltas provide diverse ecosystem services and benefits for their populations. At the same time, deltas are also recognised as one of the most vulnerable coastal environments, with a range of drivers operating at multiple scales, from global climate change and sea-level rise to deltaic-scale subsidence and land cover change. These drivers threaten these ecosystem services, which often provide livelihoods for the poorest communities in these regions. The imperative to maintain ecosystem services presents a development challenge: how to develop deltaic areas in ways that are sustainable and benefit all residents including the most vulnerable. Here we present an integrated framework to analyse changing ecosystem services in deltas and the implications for human well-being, focussing in particular on the provisioning ecosystem services of agriculture, inland and offshore capture fisheries, aquaculture and mangroves that directly support livelihoods. The framework is applied to the world's most populated delta, the Ganges-Brahmaputra-Meghna Delta within Bangladesh. The framework adopts a systemic perspective to represent the principal biophysical and socio-ecological components and their interaction. A range of methods are integrated within a quantitative framework, including biophysical and socio-economic modelling and analyses of governance through scenario development. The approach is iterative, with learning both within the project team and with national policy-making stakeholders. The analysis is used to explore physical and social outcomes for the delta under different scenarios and policy choices. We consider how the approach is transferable to other deltas and potentially other coastal areas.

The total blue carbon stock of the Bangladesh Sundarban mangroves was evaluated and the probable future status after a century was predicted based on the recent trend of changes in the last 30 years and implementing a hybrid model of Markov Chain and Cellular automata. At present 36.24 Tg C and 54.95 Tg C are stored in the above-ground and below-ground compartments respectively resulting in total blue carbon stock of 91.19 Tg C. According to the prediction 15.88 Tg C would be lost from this region by the year 2115. The low saline species composition classes dominated mainly by Heritiera spp. accounts for the major portion of the carbon sock at present (45.60 Tg C), while the highly saline regions stores only 14.90 Tg C. The prediction shows that after a hundred years almost 22.42 Tg C would be lost from the low saline regions accompanied by an increase of 8.20 Tg C in the high saline regions dominated mainly by Excoecaria sp. and Avicennia spp. The net carbon loss would be due to both mangrove area loss (~ 510 km2) and change in species composition leading to 58.28 Tg of potential CO2 emission within the year 2115.

Salinization of freshwater and soils is a global phenomenon that adversely affects 500 million people, particularly in low-lying river deltas. Impacts of salinity on food and water security and agricultural livelihoods are well documented and reviewed herein, along with additional effects on human health that have received less attention and warrant further study. Populations forced to consume saline waters display increased occurrence of diseases such as hypertension in Bangladesh, particularly among the rural poor in coastal areas. This review synthesizes knowledge on socio-hydrological drivers of salinization in large river deltas globally. Multiple drivers arise at different scales and include agricultural practices, upstream water diversion, and relative sea level rise and can be amplified through feedback from inappropriate adaptation strategies. Understanding deltas as truly coupled socio-hydrologic systems is critical to anticipate these feedbacks.

No abstract available DOI: http://dx.doi.org/10.3329/bjsr.v25i1.13048 Bangladesh J. Sci. Res. 25(1): 33-41, 2012