Introduction

The coastal regions of the world contain social and ecological systems (SES) in which complex biophysical and socio-economic processes mutually interact in a resilient and sustained manner (Redman et al. 2004). However, the vulnerabilities of coastal deltas to various natural and geological processes such as land subsidence, coastal flooding, cyclones, climate change and sea-level rise (SLR) are widely recognized (IPCC 2014). In addition, human populations are concentrated along coasts, and as a consequence, coastal ecosystems are amongst of the most impacted and altered worldwide (Adger et al. 2005). One of the main drivers causing environmental degradation and socio-economic deprivation worldwide is infrastructure development (MEA 2005), such as construction of coastal polders (generally a piece of low-lying land reclaimed from the sea or a river and protected by dykes) and road networks. The combined effect of these natural as well as anthropogenic activities is playing a major role in altering the coastal environment. Environmental management of these complex systems requires integration such as Integrated Water Resources Management (IWRM) (e.g. Rouillard et al. 2014) and Integrated Coastal Zone Management (ICZM) (Cicin-Sain 1993). A systematic assessment of trends of social and ecological processes and understanding their interconnectivity is therefore essential for coastal adaptation planning within IWRM and ICZM approaches.

Bangladesh (Fig. 1), part of one of the largest low-lying deltas known as the Ganges–Brahmaputra–Meghna (GBM) delta, is frequently quoted as one of the most vulnerable nations due to impacts of climate variability and change (e.g. Auerbach et al. 2015). More specifically, the country’s embanked southwest coastal area is often cited as the zone of major hazards and disasters such as cyclones, SLR, salinity intrusion, extreme monsoon rainfall, water logging and river flooding (Brammer 2014, Matin and Taylor 2015). This part of the coast is, however, ecologically highly valuable and extremely fertile accompanied with large, variable hydrological and geomorphological subsystems featuring densely populated human habitats and rich biodiversity. The region is the home to about 22 million people (see Supplementary Information (SI) for detail description of the region). Various anthropogenic and development activities such as construction of coastal polders, upstream water withdrawal at Farakka barrage (it is a barrage across the Ganges River, located in the Indian state of West Bengal, roughly 16.5 km from the border with Bangladesh), land use change through intensification of shrimp aquaculture, deforestation, pollution and changes in chemical fluxes have contributed to accelerated changes in the coastal zone (e.g. Hossain et al. 2016a, b).

Fig. 1
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Southwest coastal region of Bangladesh. Red circles indicate river discharge and salinity measuring stations. Green circles indicate location of major administrative areas known as district (Color figure online)

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Several recent studies (e.g. Shameem et al. 2014, Matin and Taylor 2015, Khan et al. 2015) assessed the vulnerability and resilience of rural livelihoods in southwest coastal area due to tropical cyclones, land use change and salinity intrusion. The construction of Farakka barrage and its effect on freshwater flow (Gain and Giupponi 2014), salinity (Mirza 1998) and biodiversity (Gain et al. 2007, 2008) in the area have also been studied. Swapan and Gavin (2011) assessed the impact of commercial saltwater shrimp farming on rural livelihood patterns in southwest Bangladesh using participatory methods. Auerbach et al. (2015) assessed the impacts of polder constructions on sediment deposition and distribution. However, these studies do not provide a comprehensive picture of SES of the southwest coastal area. Most recently, Hossain et al. (2016a, b) made an attempt to provide an integrated picture on the interrelationship between ecosystem services and human well-being in the area, rather than focusing on social and ecological processes considering dominant drivers and its impacts. A scientific understanding of socio-economic and ecological functioning and their changes is still a major gap in the southwest coastal area in support of integrated coastal zone management.

The objective of this study is to provide a historical perspective on physical, social and development change of complex social ecological system that contributes to the understanding of the “change process” of southwest coastal region of Bangladesh. The change process of SESs is described based on the drivers–pressure–state–impact–response (DPSIR) framework. The DPSIR is a useful adaptive management tool for analysing and identifying solutions to SESs (Gari et al. 2015). Recently, Hossain et al. (2015a, b) applied DPSIR framework for exploring the integration of ecosystem services and climate change adaptation in coastal wetlands in Bangladesh. We have applied DPSIR framework to provide a comprehensive overview of social ecological system in southwest coastal area. The information from the DPSIR analysis can be used to develop integrated management decision (within ICZM and IWRM framework) in the study area.

Conceptual framework

The DPSIR framework is developed by the Organization of Economic Cooperation and Development (OECD) and the European Environment Agency (EEA) for the adaptive management of social ecological systems (EEA 1999). According to the DPSIR framework, there is a chain of causal links: “driving forces” such as social and economic developments exert “pressures” on the environment (e.g. pollutants) and, as a consequence, the “states” (physical, chemical, biological) of the environment changes. This leads to “impacts” on e.g. human health, ecosystems and materials that may elicit a policy “response” that feeds back on the driving forces, on the pressures or on the state or impacts directly, through adaptation.

The implementation of this framework (Fig. 2) for the southwest coastal area highlighted the specific features of each DPSIR element: (i) the assessment of drivers provides the identification of the major driving forces affecting the area, (ii) the pressures highlight the ways that these drivers are actually expressed, (iii) the state provides the current socio-economic and environmental status of the system, (iv) the impacts identify the causative effects on ecosystem and society, and (v) the response is the evaluation of management practises and the policy measures for sustainable socio-economic development of the area.

Fig. 2
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Conceptual framework of study

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This study assumes that the complex and dynamic regional and local changes in the socio-ecological processes of this coastal zone are co-determining and interacting at various levels, although the linkages between the processes are yet not fairly understood. Thus, the application of the DPSIR model requires an appropriate list of indicators “site-specifics” in order to describe the complex ecological and socio-economic processes in the studied area. Reviewing the literature (Sebesvari et al. 2016), a number of several indicators are available mirroring the anthropogenic stressors and the quality of the river basins. The long-term changes in the co-evolutionary coastal system of southwest Bangladesh was investigated based on available peer-reviewed literature. However, in order to support our findings, we have used time series data for the following variables: temperature, rainfall, discharge, SLR, river sinuosity, waterlogging, river salinity, coverage of shrimp culture, soil salinity, ground water level, land use change and modification, land subsidence, cyclones and diversity in the Sundarbans (mangrove forest). Details of the time series data, their time span and sources are summarized in Table 1. In order to observe past changes for these primary data, we have analysed trends in time series with the application of parametric and non-parametric statistical methods (see Electronic Supplementary Information for details).

Table 1 Time series of environmental change observations in SW Bangladesh
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Historical perspectives on drivers, pressures, states, impacts and responses

Drivers and pressures

Both natural and anthropogenic driving forces such as climate change, upstream development, geological process, land use change and global economy play important roles for the changes in the SESs in southwest coastal area. Table 2 presents a summary of the spatio-temporal changes in the drivers and pressures within the regional boundary of southwest coastal region.

Table 2 Summary of spatio-temporal changes found within the regional boundary of the southwestern coastal zone
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Climate change and sealevel rise

Turner and Annamalai (2012) reviewed climate change in South Asia and found that the Indo-Pacific oceanic warm pool has warmed up over last 50 years and potentially supplied increased amount of moisture during the monsoon in the region although observation suggests that monsoon rainfall has not been increased. A more recent study by Loo et al. (2015) further explained the phenomena as, 1970s onwards, there is a westward shift of Indian summer monsoon, which leads to a delay of few days the onset of the monsoon and a 15-day delay of the onset of the monsoon in the future is predicted. Based on 22 years (1977–1998) measured sea-level data, the meteorological research council of the South Asian Association for Regional Cooperation (SAARC) found that the rate of SLR at the coast of Bangladesh is much higher (from 4 mm year−1 at western part to 19 mm year−1 at eastern part) than the global rate of 1.0–2.0 mm year−1 in the last century (Brown and Nicholls 2015).

Geological activity

The study area is located in the lower reaches of the Ganges–Brahmaputra–Meghna (GBM) river basin, which is geologically one of the youngest and tectonically most active denudation regimes of the world. The GBM river system carries the world’s highest annual sediment load (∼1 × 109 t a−1) (Goodbred and Kuehl 2000a, b). Therefore, sediment deposition historically played a major role of developing the area. Over the past several thousand years, eastward migration of Ganges (due to geologic process) has led to effectively cut off fluvial sediment and a major share of freshwater flow in the southwest coastal area (Allison et al. 2003, Hore et al. 2013). Land subsidence due to crustal movement and compaction of the recent sediment also contributed to SLR. Hanebuth et al. (2013) observed that in last 300 years, the Sundarbans region is sinking at a rate of 5.2 ± 1.2 mm year−1, while Brown and Nicholls (2015) recently reported that the average subsidence rate in the region is about 8.8 mm year−1 over last 1000 years, which actually has doubled over last 10,000 years. The erosion and accretion also played an important role in coastal changes. Rogers et al. (2013) estimated the recent annualized accretion rates as about 1.1 cm year−1. Allison (1998) observed that the whole delta front is active and prograding at a rate of 7 km year−1 over last 200 years. However, the western front of the southwestern region is at a state of small net erosion as the sea-facing shoreline has retreated about 3–4 km since 1792 while the eastern front is showing small net accretion since 2000 (SI Fig. S6).

Upstream development

Since the study area is located in the downstream of the GBM river basin, upstream development activities such as construction of barrages, dams and reservoirs in India, China, Nepal and Bhutan have significant implication on freshwater and sediment flow in the study area. Most importantly, the commissioning of Farakka barrage in India in 1975 to withdraw Ganges water during dry season played a major role on freshwater supply and sediment deposition in the southwest coastal region (Mirza 1998; Gain and Giupponi 2014).

Land use change and other human interventions

Conversion of agriculture and mangrove forest to brackish water aquaculture has been one of the most evident drivers of changes in southwest coastal area (Datta et al. 2010; Islam 2014). Being a traditional practice, shrimp culture was usually restricted between the levees and the river channels. However, driven by the foreign demand, over the last three decades (post-1980s), such practice has increased in spatial coverage within the polder systems. Using 13-year (1999–2012) remote sensing data, Khan et al. (2015) found an overall 30% increase in shrimp culture, while 48% decrease in agricultural land. Since the late nineteenth century, other human intervention, for example, reclamation work (i.e. closing small channels) also contributed to change in coastal processes (Hunter 1877, Williams 1919).

Global economy

Due to global increasing demand of shrimp and its higher economic return, aquaculture is undertaken largely in southwest coastal region of Bangladesh (Datta et al. 2010). The lands were utilized for paddy cultivation before shrimp culture activities commenced in early 1980s.

States

Hydro-meteorological changes

Analysis of eight meteorological stations (i.e. Khulna, Jessore, Barisal, Satkhira, Faridpur, Mongla, Patuakhali and Bhola) over southwest Bangladesh reveals that the average annual temperature is increasing significantly at a rate varying from 0.006 to 0.024 °C per year since 1948. This increasing trend has intensified since the post-1990s (0.05∼0.1 °C year−1). In contrast, annual rainfall varies widely in the region and shows no stable trend over the time except for Jessore, Faridpur and Barisal. However, it is found that cumulative post-monsoon (September–November) and winter (December–February) rainfall is increasing in the region as a whole (SI Figs. S1 and S2). This increasing trend in post-monsoon and winter rainfall is possibly associated with the occurrences of post-monsoon cyclones rather than pre-monsoon cyclones (Kandalgaonkar et al. 2005).

Cyclones and storm surges

Over the period of 1877–2014, about 123 cyclones and tropical depressions (TD) made landfall in Bangladesh. Examination of the time series data suggests that about 60% of those cyclones and TDs made landfall in the southwest coastal region. Trend analysis reveals that severe cyclonic storms with hurricane intensity have increased over the Khulna coast since 1980 (SI Fig. S8). This intensification of severe cyclones is likely to be linked with the increasing sea surface temperature and high enthalpy flux exchange with available moisture content during post-monsoon over the Bay of Bengal (Vissa et al. 2013).

Changes in river system

River Gorai is the principal distributary of the Ganges and major source of fresh water in the region. Historical average annual discharge records (1934–2007) show that the Ganges flow is decreasing significantly at a rate of ∼19 m3 s−1 a−1 at Hardinge Bridge (10 km upstream to origin) especially after late 1950s (SI Fig. S9). The Gorai, as a consequence, is losing its flow at a rate of ∼5.2 and ∼8.2 m3 s−1 a−1 measured at Gorai Railway bridge (∼10 km from origin) and Kamarkahali (∼50 km from origin), respectively. There is a major shift of trend after 1981 (avg. ∼10 m3 s−1, measured at Gorai Railway Bridge) where the river lost about an order of a magnitude of its annual minimum flow compared to that of the 1960s (average ∼110 m3 s−1). The decreased river flow is attributed to the combined effect of upstream development such as construction of Farakka barrage (Mirza 1998; Gain and Giupponi 2014) and geological activity such as eastward migration of Ganges due to neotectonic movement in the southwest (Hore et al. 2013). Over the course of time, Gorai–Madhumati system has shown increased sinuosity (measured as the actual path length divided by the shortest path length of a curve, with a value ranges from 1 (case of straight line) to ∞ (case of a closed loop)) in the recent hundred years which ranges between 1.1 and 1.3 (Halcrow et al. 1993) with the lower half of the channel representing higher sinuosity (1960–2010 avg. = ∼2.3) than that of the upper half (1960–2010 avg. = ∼1.3) (SI Fig. S3 and S4). Due to increase of energy loss and decrease of channel slope, Gorai’s ability of transporting water and sediment in the upper reaches is getting impaired with time. As a consequence, the major river system draining southwest became disconnected from its source during 1950s and lost fresh water supply and energy to carry sediment along the course.

Tidal range and ESLR

Tide gauge analysis of Bhairab–Rupsha River system (in Khulna) over the period 1937–2010 indicates that the maximum tidal height is increasing at a rate of ∼18 mm a−1 while the minimum tidal height is decreasing at a rate of ∼8 mm a−1 (SI Fig. S5). Pethick and Orford (2013) observed that relative mean sea-level rise (RMSL) ranges from 8.8 mm a−1 at the mouth of the Passur estuary to 2.8 mm a−1 at Khulna, some 120 km from the mouth. However, they argued that the spatial trend of effective sea-level rise (ESLR), which takes land subsidence, tidal amplitude, eustatic sea-level and freshwater input into account, tends to be the opposite of RMSL: being low at the mouth of estuary (10.9 mm a−1 in Hiron point at the coast), higher at the origin of the estuary (14.5 mm a−1 at Mongla) and highest at the poldered region (17.2 mm a−1 at Khulna). They attributed this phenomenon to construction of coastal polders.

Changes in river salinity

All the downstream stations that exhibit tidal characteristics show significant upward trends in salinity—Jhikargacha ∼231 μS cm−1 a−1, Paikgacha ∼2160 μS cm−1 a−1, Khulna ∼83 μS cm−1 a−1 and Mongla ∼1007 μS cm−1 a−1. Decreased river discharge as well as SLR and intensive aquaculture is responsible for changes in river salinity (Bhuiyan and Dutta 2012; Shaha and Cho 2016).

Waterlogging

Waterlogging has become evident in the region over last three decades especially in the areas adjacent to the coasts of Jessore, Satkhira and Khulna Districts. Analysis indicates that in Jessore region, waterlogging has expanded to ∼600 km2 since 1980 at a rate of ∼20 km2 per year. The rate for Satkhira is ∼25 km2 per year since 1980 (∼755 km2 area under waterlogging in 2014) (SI Table S1). As a whole, waterlogging is expanding from northeast to southwest. The intensive water logging is attributed to the intensive shrimp farming, sedimentation in the river bed and unplanned human activities.

Soil salinity

Soil salinity data over the period of 1970–2009 shows that area under saline soil is increasing rapidly in the region at a rate of 5875 ha year−1. Although salinity classes exhibit temporal variation, it is evident that since 1970, areas are transforming into high soil salinity class (EC >15 ds m−1) at a rate of 7044 ha year−1. While area under slight (EC <4 ds m−1) and slight to moderate (EC = 4–8 ds m−1) class salinity is decreasing, area under moderate to high (EC = 8–15 ds m−1) and high (EC >15 ds m−1) is increasing in this region (SI Table S2).

Impacts

The changes of states of different variables due to climatic, manmade and geologic drivers have created different order effects on society and economy in southwest coastal area.

Land use change and coastal aquaculture have multifarious consequences to the social–ecological system of the study area. Deb (1998) found that the labour requirement for on-farm activities in shrimp farming is only one fourth to that of traditional agricultural activities. Therefore, shrimp culture and water logging negatively affected agro-based labour force for the coastal communities, causing outward seasonal migration and even permanent migration, in extreme case (Ackerly et al. 2015). Roy et al. (2009) reported existence of human-made breaches in the polders attributed to shrimp farming and linked the event of embankment failure during cyclone Aila (hit southwest coast on 25 May 2009). Several analyses have also linked shrimp farming with weakening embankments and thereby increasing the risk of embankment failure in the face of storm surges (Vivekananda et al. 2014). Besides, the increasing number and magnitude of hazards/disasters are affecting the land use pattern, which in turn degrading the community resources and capacities (Huq et al. 2015), and have consequences on agricultural production as it increases soil salinity (Worland et al. 2015) as well as degrades the availability of fresh water as well as biodiversity. Similar findings have been confirmed by Hossain et al. (2016a, b) as they have reported that rice production has reduced poverty alleviation and increment of gross domestic product (GDP) growth, whereas deteriorated water quality impacted on economic growth.

The people of Bangladesh have improved their ability to cope with disastrous events, like cyclone, river bank erosion, flooding or even waterlogging and salinity. For example, the death toll of cyclone Gorkey in 1991 was 130,000 whereas the similar kind of cyclone Sidr of 2007 was 3400 deaths. Disasters often has caused displacement or forced migration in the region. According to the International Organization for Migration (IOM) (IOM 2009), many people have migrated from the coastal zones of Bangladesh to urban low-income areas due to frequent cyclones, storm surges, river erosion and other environmental occurrences. Mallick (2014) described that the process of disaster-induced rural–urban migration had been dramatic in 1970, when a strong cyclone hit the coastal regions of the country with a subsequent death toll of ∼300,000. In 2007, 2008 and 2009, three severe cyclones—Sidr, Nargis and Aila—hit the southern coastal region of Bangladesh. During cyclone Aila in 2009, an estimated 40,000 people were displaced (Roy et al. 2009). This number, including forced migration, may have reached up to ∼120,000 due to prolonged waterlogging until 2010 and with many households deciding to migrate to other locations (Mallick and Vogt 2013). Mallick and Siddiqui (2015) indicated that people in the vicinity are forced to change their original agrarian occupations to non-agrarian occupations, thus creating lack of job opportunity, unemployment and migration. Hasan et al. (2013) have mentioned that over 35 million people will have to leave the coastal areas (southeast and southwest of Bangladesh) due to an anticipated 45 cm SLR by 2050. All these facts indicate that there is a close relationship between extreme climate events, water logging and coastal aquaculture (i.e. shrimp farming requires one-fourth labour force of rice production, therefore, during shrimp season, a huge number of poor income people seasonally migrate in nearby places for alternative income sources), immediate displacement and long-term migration patterns.

Changes in river discharge and salinity have created a major impact on Sundarbans, the world’s largest single tract mangrove forest. It provides a wide range of ecosystem services and contributes to socio-economic development of the neighbouring communities. According to Maitra (1914), the Sundarbans was naturally measured around 16,000 km2 sometime around 1770s. Given its current extent (10,000 km2 of which ∼60% is in Bangladesh), Sundarbans has lost about one third of its original extent. Aziz and Paul (2015) analysed Landsat imagery over 1989–2010 to find formation of numerous small creeks and channels prior to 2000, which actually reduced ∼28% of Heritiera fomes (locally known as Sundari tree) cover in the extreme northern part of the mangrove. Iftekhar and Saenger (2008) reported a decline in both H. fomes and Excoecaria agallocha (locally known as Gewa)-dominated forest cover at a rate of 0.23–0.27% a−1 over the period of 1926–1997. Chowdhury et al. (2008) estimated that H. fomes trees are affected by “top-dying” diseases and its coverage has declined by 76% since 1959. They also reported evidences of dramatic declines in other mangrove species. H. fomes is economically a high value tree that is used for paper pulp and known to grow along the freshwater dominant areas of the tidal zones. These impacts are associated with decreases in fresh water flow, SLR, geologic land subsidence, coastal aquaculture and shrimp farming. Sarkar et al. (2016) claimed that Ganges’s freshwater flow into the Sundarbans has dropped from 3700 to 364 m3 s−1 since the commissioning of the Farakka barrage in India in 1975.

Transformation in land use from rice cultivation to shrimp farming affected different populations differently. This process exacerbated inequalities amongst people in poverty (Ackerly et al. 2015). The most vulnerable are those who depend on day wages and those who face a family crisis, like daughter’s marriage, sudden death of earning member, health crisis and costly diseases. (Ackerly et al. 2015), and sometimes, they need to choose seasonal or temporary migration to nearby cities and/or communities as an alternative livelihood option (Mallick 2014).

Despite the presence of waterlogging and salinity, agricultural (crop and fisheries) production and GDP have increased and poverty has been reduced in the region. Evidences show that since 1961, rice production has been rising steadily in the southwest Bangladesh, which intensified post-1995 (Hossain et al. 2016a, b). The reason behind increased agricultural production is the use of high-yielding varieties (HYV) replacing the local varieties. Similarly, the production in inland fishes, marine fish catches and shrimp production have also been increased between 1980 and 2010 (Hossain et al. 2016a). The continuous and increasing inflow of foreign remittances is also a great contributor to the GDP increment. As an outcome, GDP is increased and poverty is declined ∼17% across the coastal zone since 1995 (Hossain et al. 2016b). However, future projections suggest that due to SLR, agriculture production can be reduced and hence this will negatively affect the GDP and poverty (de Araujo Barbosa et al. 2016).

Response

Development projects

Both natural and human interventions have shaped the southwestern coastal region over centuries. As discussed earlier, literatures that go back up to sixteenth century suggest that, while geology has played a major role in the delta development process, human interactions have also contributed towards modification of delta development. Over the time, humans on this delta have responded to these changes, whether the changes inflicted by nature or themselves. As a result, in recent times, this coastal region has also seen many development projects related to water management: for example, Coastal Embankment Project (CEP) (1968 onwards), Small-Scale Water Resources Sector Project (1996–2002), Gorai River Restoration Project (1998–2007), Integrated Planning for Sustainable Water Management (IPSWAM) (2003–2008), Coastal Zone Development Program (CZDP), Coastal Embankment Rehabilitation Project (CERP) (1996–2002) and Khulna–Jessore Drainage Improvement Project (1994–2002). These projects have significantly modified the land use pattern as well as morphological processes in the region (Nandy et al. 2007). For example, the main objective of CEP was to convert the seasonally flooded coastal wetlands into reclaimed land for permanent agricultural as well as to establish human settlement protected from saline intrusion, cyclones, and tidal waves, (Gain et al. 2017). A series of 37 polders with 1566-km-long embankment and 282 sluice gates were constructed under CEP (Halcrow et al. 1993). During the construction, numerous channels were cut-off, modified and closed. The system worked fine for the first decade as crop production raised twofold to threefold, but improper operation, poor management and failure to take the topography and regional sedimentation pattern into account led the polder malfunction (Kibria 2006). The construction of the CEP has caused a major change to the transitional processes that were already in place in the region prior to 1960s. After the 1960s, the volume of tidal over spill has greatly reduced, which is resulting in insufficient tidal ebb discharge to sustain pre-polder channel cross sections and subsequently contributing to rapid silting up of the both sides of the polders (Awal 2014).

Indigenous human responses

While institutional responses to the changes in this coast have been thorough development projects, community-wise people have responded to the changes in their own ways. Before polders, building temporary earthen embankments alongside rivers to prevent high waters was a common practice amongst coastal people. After the implementation of the CEP, which introduced permanent embanking system that led to short supply of sediment (and source of crop nutrition) inside the polder, communities responded with the idea of river basin management, known as the tidal river management (TRM) (Gain et al. 2017). The idea basically revolves around letting high water in to deposit sediment carried by it through intentional breaching of the polder at points close to river (Roy 2004). Although such idea has been proven to have social and technical difficulties (for example, it causes erosion and population displacement), a few successful experiments exist. Another recent response has been identified as reopening former channels that were closed during polderization. This technique efficiently brings tidal excess tidal spill inside the polder and reintroduces fresh sediment inside. Shifting of shrimp to rice to avoid saltwater intrusion, cropping alongside the river levees outside polder system, excavating and transporting riverside soil inside polders to grow vegetables, etc. have been of indigenous responses lately (last decade or so). Beside, with the aid of government and non-government agencies, communities in the southwest coast are responding to the monsoon shift, increasing temperature, lack of freshwater flow and sediment through crop rotation, crop alteration, water conservation during post-monsoon, river born soil shifting and many other locally adopted techniques.

Discussions and conclusion

We examined how the coastal processes may interact with the existing human interventions through DPSIR framework. Our findings suggest that current coastal management (see “Response” section) such as implementation of CEP is not sustainable which again negatively contributed to drivers, pressures, states and impacts. The presented framework is highly useful in structuring and prioritizing information needs in support monitoring design for integrated management in southwest coastal area.

Recently, tidal river management (Dewan et al. 2015; Gain et al. 2017; Hossain et al. 2015a, b), river basin management (Gain and Schwab 2012) and delta plan (http://www.bangladeshdeltaplan2100.org/) are ongoing management strategies of the government of Bangladesh in southwest coastal area. Evaluating each of these management options by using DPSIR framework presented here can provide a comprehensive picture of the study area. For example, successful implementation of tidal river management can reduce water logging and enhance river flow, which can provide positive impact on agricultural production and other higher-order impacts. However, unplanned and poor design could lead to erosion and population displacement as happened in the Pakhimara Beel this year. Effective transboundary cooperation through applying river basin management approach with India and other upstream countries can ensure freshwater supply during dry season, which can reduce salinity in the southwest coastal region. This will create positive impact on biodiversity and forest ecosystem (Gain et al. 2008). Thus, reliable information and knowledge on changes in the social–ecological systems and comprehensive causes of those changes can be effectively analysed through the approach presented here, which can support decision making southwest coastal area.

The human history of intervention and socio-ecological changes in the southwestern coast of Bangladesh are inseparable. The application of DPSIR framework suggests that the region is already facing severe problems that might be worsening at an accelerated pace. This study synthesizes the historical biophysical and human intervention database to explore the ways that the people and nature here are interconnected and mutually co-existed. It also gives us the understanding that the dynamism of the southwest coast demands detailed, long-term and site-specific information to comprehend the mechanisms in play. To negotiate such situation, we need to be prepared with knowledge, proper plan and economic strength.

It is essential to make site-specific detail assessments of socio-ecological integrity of this region in relation to the future threats of SLR, salinity, waterlogging, cyclones and storm surges and displacements. Monitoring institutions that provide biophysical information need to be updated and strengthened. Institutional and political arrangements that are to implement the coastal planning and management are to be equipped with scientific knowledge, awareness and manpower and to be blessed with local people’s experience and cooperation. A range of studies are needed to develop such integrated coastal management plans in Bangladesh. Putting all the pieces together is the utmost step towards integrating the ideas of river basin management into a complete coastal zone planning. A holistic approach is therefore required to adjust delta changes.