Urbanisation and differential vulnerability to coastal flooding among migrants and nonmigrants in Bangladesh

Abstract

Like much of Asia, Bangladesh will see an urban transition in the coming decades. Yet, its urbanisation will be unprecedented in terms of climate vulnerabilities. Little is known about urbanisation and migrants, in the context of these vulnerabilities, in part because demographic inquiry and training (with a few notable exceptions) has only begun in the last decade to embrace new, spatial data and methods of analysisespecially those involving earth-observing satellites. This descriptive analysis examines urban change along with low-elevation coastal zone (LECZ) data as a proxy for flood exposure, using data from satellites, and integrates those features with socioeconomic characteristics and migration information from demographic and health survey data (DHS 2000-2014). We describe where urban change has occurred in the past 40 years, with a focus on understanding change occurring in LECZ areas. We then describe vulnerabilities of the households and migrants in areas of urban change from about 2004 onward, both in terms of their potential exposure to flooding and socioeconomic characteristics. We find that moderate-risk, 7-10m LECZ areas are not only more built-up than higher elevation areas, but they have also had appreciably more urban development as measured by built-up change than other areas. Although we found that poor urban households are more likely to be located in flood-prone areas, poor households were also less likely to be in areas that are built-up. The 0-6m LECZ has lower proportions of urban in-migrants, but among those migrants to cities, the flood-prone LECZ is more likely to be the destination of poor migrants. This paper suggests that climate adaptation plans should be spatially specific because poor migrants are more likely to be located in LECZ areas that are more prone to flooding.

Estimating population and urban areas at risk of coastal hazards, 1990–2015: how data choices matter

“…(GHSL measures area, not volume, such as the vertical dimension of built-up areas or cities.) Elsewhere these data have been used to describe change in the extent or footprint of the urban environment (Balk et al, 2018) and as an indicator for urbanization of land area (Liu and Balk, 2020;Pinchoff et al, 2020;Gao and O'Neill, 2020). We use it independently to evaluate how much land in the LECZ is built-up.…”

Estimating Population and Urban Areas at Risk of Coastal Hazards, 1990–2015: How data choices matter

“…(GHSL measures area, not volume such as the vertical dimension of built-up areas or cities.) Elsewhere these data have been used to describe change in the extent or footprint of the urban environment (Balk et al, 2018) and as an indicator for urbanization of land area (Liu and Balk, 2020;Pinchoff et al, 2020;Gao and O'Neill, 2020). We use it independently to evaluate how much land in the LECZ is built-up.…”

Looking Back, Looking Forward: Progress and Prospect for Spatial Demography

“…In an earlier commentary (Balk, 2011), we argued that the demographic study of urbanization requires that demographers and allied fields adopt spatial tools and methods as their own, beginning by integrating key geographic concepts in their thinking. While spatial approaches are becoming more widespread (Balk et al, 2018;Donaldson & Storeygard, 2016;Henderson et al, 2012), especially in studies on the interactions of population and the environment (Kugler et al, 2019;Liu & Balk, 2020), they remain far from commonplace and are mostly implemented by researchers from allied social science disciplines.…”