The effects of changing land use and flood hazard on poverty in coastal Bangladesh
Introduction
It is widely recognised that poor people are disproportionately exposed to environmental hazards (Winsemius et al., 2018). There are several possible reasons for this. For instance, poor people tend to inhabit remote low-lying floodplains, due to the limited development opportunities and relatively cheaper lands (Dasgupta, 2007). Their livelihoods and assets are less protected (Bangalore et al., 2019; Hossain et al., 2012), and thus, they have relatively a low capacity to cope with property losses resulting from flooding (Brouwer et al., 2007).
Bangladesh is located in the floodplain of three major rivers — the Ganges, Brahmaputra, and Meghna. The combined discharge generated of these three rivers is the highest in the world. The peak run-off depth is also the highest, which, combined with storm surges generated from the Bay of Bengal. This makes a major portion of the country is prone to flooding (Dasgupta, 2007). Flood processes in the coastal region of Bangladesh are complex, as it can occur from multiple sources such as intense precipitation during the monsoon, high water levels in the rivers, and cyclone induced storm surges (Adnan et al., 2019). Different environmental stresses create biophysical and socioeconomic challenges in the coastal region. For instance, frequent flooding and increasing soil salinity limit agricultural productivity, which is the main source of livelihoods in coastal Bangladesh (Rahman et al., 2020).
Flood management approaches in the coastal region of Bangladesh include both structural and non-structural measures (Paul and Rashid, 2017; Rahman and Salehin, 2013). Major surge events induced by cyclones in the 1950s forced the then government to invest in the Coastal Embankment Project (CEP) in the 1960s. The CEP aimed at increasing agricultural production to ensure food security, by preventing salinity intrusion in the coastal region particularly during the dry season. As a part of the CEP, 139 polders (enclosed coastal embankments) were created in between the 1960s and 1980s (Islam et al., 2016; Warner et al., 2018). The construction of the polders has brought both beneficial and harmful effects on society and the environment. The protection from flooding afforded by embankments led to an increase in agricultural productivity until the 1980s (Adnan et al., 2020). Embankments have demonstrably protected the polder area against storm surges and fluvio-tidal floods of moderate severity (Adnan et al., 2019). However, the separation of floodplains from adjacent rivers caused geomorphological changes in the polder areas, exacerbating land subsidence inside polders (Auerbach et al., 2015). Accelerated land subsidence and inadequate drainage are accountable for frequent pluvial flooding (locally called ‘waterlogging’) (Adnan et al., 2019).
Generally, the construction of structural flood control measures, such as polders, shapes the pattern of human settlements and land use, which in turn impacts the extent of flood risk. Such flood control measures create the so-called “levee effect” (White, 1945). Whilst people tend to settle in less flood-prone areas, presence of structural flood defence system encourages floodplain development by engendering a sense of safety (Di Baldassarre et al., 2013; Montz and Tobin, 2008). Therefore, the failure of structural systems in the form of overtopping or breaching of embankments may exacerbate flood damages (Hui et al., 2016).
The pattern of land use/land cover (LULC) in the coastal region of Bangladesh has experienced major changes over the past half-century, following the construction of polders (Abdullah et al., 2019; Huq et al., 2015; Khan et al., 2015; Parvin et al., 2017; Rahman et al., 2017). Such changes largely occurred due to frequent and diverse natural hazards (e.g., floods) and increases in inundation, soil salinity, and land erosion (Brouwer et al., 2007; Khan et al., 2015). For instance, about 1% of agricultural land along the south western coast was transformed into non-agricultural use in each year over the past four decades due to the occurrence of frequent flooding (Rahman et al., 2017). The transformation of agricultural land to shrimp culture has been a common practice in the area since the 1980s as it can be more profitable (Khan et al., 2015). However, such land transformation has reportedly been leading to an increase in soil salinity, reducing agricultural production (Khan et al., 2015; Rahman et al., 2017).
Whilst anthropogenic drivers profoundly change the pattern of LULC, such transformation of land may affect local flooding processes (Wheater and Evans, 2009). The pattern of LULC determines the amount of runoff generated during a precipitation event, thus, influencing the water balance in an area. Hence, LULC may affect both the probability of flooding and its consequences (McColl and Aggett, 2007; Szwagrzyk et al., 2018). Flood losses are not only dependent on extreme hydro-meteorological conditions of a region, unplanned land use can multiply property damages (Lee and Brody, 2018). In coastal Bangladesh, unplanned LULC change may lead to environmental degradation such as soil salinization, disappearance of seasonal lagoons, and deterioration of water quality by increasing salinity (Islam et al., 2015).
Generally, flooding and poverty coexist particularly within rural communities, as damages caused by recurring flood events deplete assets, negatively impact agricultural incomes and thus lower quality of life of communities (Dube et al., 2018). It has been hypothesised that increasing flood risk and unplanned LULC change may create a poverty trap in the coastal region of Bangladesh (Ahmed, 2018; Borgomeo et al., 2017), inhibiting long-term development prospects (Parvin et al., 2017). Marginalised farmers could not generate adequate income through agricultural activities, whilst being unable to transform their agricultural land into aquaculture due to high cost associated with such change (Islam et al., 2015). As a result, they are unable to migrate out of such areas due to social and economic constraints and related costs (Dasgupta, 2007).
Regulating LULC change is an intervention to reduce flood risk, which has been adopted in different coastal cities (Adnan and Kreibich, 2016). Therefore, it is essential to understand the association between LULC and flood risk. Risk-based flood management approaches have received attention globally due to recent experience of several catastrophic events in many regions across the world (Hall et al., 2015, 2003b; Poussin et al., 2015), as well as the projected increase in the frequency and severity of flooding due to climate change-induced sea level rise (Koks, 2018). An empirical analysis of flood risk can support decision-makers to appraise and sequence investments for flood management (Dawson et al., 2011; Hall et al., 2003a, 2019; Hino and Hall, 2017; Sayers et al., 2002). The methods used in research and practice for quantifying flood hazard and vulnerability range from simple approaches (with numerous simplifying assumptions) to very complex applications, which are both data and time-intensive and computationally expensive (Apel et al., 2009; Dewan, 2013).
In the existing literature, the association between flood risk and poverty has been comprehended primarily by estimating exposure of poor people to flooding at various geographical scales (Bangalore et al., 2019; Brouwer et al., 2007; Qiang et al., 2017; Winsemius et al., 2018). In the case of coastal Bangladesh, a few studies have applied quantitative approaches (based on household survey data) to show how poverty exacerbates flood vulnerability/risk (Akter and Mallick, 2013; Brouwer et al., 2007). However, little is known about (i) how the pattern of LULC change influences flood risk at present and in the future; (ii) what is the association between LULC change and risk of flooding, and how they impact poverty spatially. We address these questions by estimating: (i) flood risk in relation to current and future LULC scenarios; and (ii) the change in poverty in relation to a change in LULC and flood risk.
Section snippets
Materials and methods
This study was conducted in three stages. First, a model was established to analyse spatiotemporal patterns of LULC change and predict future LULC. Second, pluvial flood hazard was modelled to simulate the depth and extent of inundations for various return periods of monsoonal precipitation. Then flood risk was estimated at each LULC scenario (historical and future), for different flood return periods. Finally, a spatial regression model was developed to estimate poverty, incorporating
Temporal change of LULC
Fig. 4(a) shows temporal changes of observed LULC from 2005 to 2019 and their spatial variations are presented in Figure S2 (see supplementary document). From 2005–2010, a significant decrease in agricultural land was observed, while the proportion of aquaculture category increased substantially. More than 50 % of agricultural lands transformed into aquaculture use, with another 25 % into rural settlements. Contrarily, LULC change from 2010 to 2019 was relatively stable, when the main
Discussion
Monitoring and managing LULC changes have been recognised as an essential geographic phenomenon for guiding socio-economic development (Corner et al., 2014; Shahbazian et al., 2019). This study analysed and simulated LULC changes in the south western embanked area of Bangladesh to understand their association with flood risk and poverty. The study results indicated that the proportion of agricultural lands decreased significantly between 2005 and 2019. This result is similar to a few other
Conclusion
This study quantified the degree of influence of LULC change and flood risk on poverty in the south western embanked area of Bangladesh. Poverty was estimated, in terms of WI, for the present-day and for future LULC and flood risk scenarios. The analysis indicated that the area has been experiencing a rapid LULC change, resulting in a significant decrease in agricultural lands, while the proportion of aquaculture lands increased consequently. Based on the recent pattern of changes, LULC was
CRediT authorship contribution statement
Mohammed Sarfaraz Gani Adnan: Conceptualization, Methodology, Software, Formal analysis, Validation, Writing - original draft, Writing - review & editing. Abu Yousuf Md Abdullah: Investigation, Resources, Software. Ashraf Dewan: Investigation, Resources, Software. Jim W. Hall: Conceptualization, Supervision, Validation.
Acknowledgements
This work is an output from the REACH programme (www.reachwater.org.uk) funded by UK Aid from the UK Department for International Development (DFID) for the benefit of developing countries (Aries Code 201880). However, the views expressed, and information contained in it are not necessarily those of or endorsed by DFID, which can accept no responsibility for such views or information, or reliance placed on them.
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