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

Abstract

Abstract. The accurate estimation of population living in the low-elevation coastal zone (LECZ) – and at heightened risk from sea level rise – is critically important for policymakers and risk managers worldwide. This characterization of potential exposure depends on robust representations not only of coastal elevation and spatial population data but also of settlements along the urban–rural continuum. The empirical basis for LECZ estimation has improved considerably in the 13 years since it was first estimated that 10 % of the world's population – and an even greater share of the urban population – lived in the LECZ (McGranahan et al., 2007a). Those estimates were constrained in several ways, not only most notably by a single 10 m LECZ but also by a dichotomous urban–rural proxy and population from a single source. This paper updates those initial estimates with newer, improved inputs and provides a range of estimates, along with sensitivity analyses that reveal the importance of understanding the strengths and weaknesses of the underlying data. We estimate that between 750 million and nearly 1.1 billion persons globally, in 2015, live in the ≤ 10 m LECZ, with the variation depending on the elevation and population data sources used. The variations are considerably greater at more disaggregated levels, when finer elevation bands (e.g., the ≤ 5 m LECZ) or differing delineations between urban, quasi-urban and rural populations are considered. Despite these variations, there is general agreement that the LECZ is disproportionately home to urban dwellers and that the urban population in the LECZ has grown more than urban areas outside the LECZ since 1990. We describe the main results across these new elevation, population and urban-proxy data sources in order to guide future research and improvements to characterizing risk in low-elevation coastal zones (https://doi.org/10.7927/d1x1-d702, CIESIN and CIDR, 2021).

Exploring spatial feedbacks between adaptation policies and internal migration patterns due to sea-level rise

“…Sea-level rise (SLR)-related migration has received increasing attention in recent years, particularly as the impacts of SLR, such as submergence of low-lying land, saltwater intrusion, increasing coastal erosion as well as more frequent and intense coastal flooding due to extreme sea levels (ESL) may threaten the livelihoods of entire islands or nations 17 – 19 . Also, beyond small island states, SLR will affect internal migration flows considerably, mainly driven by highly urbanized coastal areas 20 – 23 . In 2010, about 27% of the global population and 34% of the urban population lived in a coastal strip that covered 9% of the global land area 21 .…”

Mapping 21st Century Global Coastal Land Reclamation

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Coastal regions face enormous pressure from the burgeoning human footprint (Doney, 2010;Halpern et al, 2019;Smart et al, 2021). Population living in the Low Elevated Coastal Zone (LECZ), which was approximately between 750 million and 1.1 billion people in 2015 (MacManus et al, 2021a(MacManus et al, , 2021b, is estimated to increase by up to 71% by 2050 (Kulp & Strauss, 2019). Urban expansion in the coastal zone, creating multi-purpose spaces including ports, industry, commerce, housing, and places for entertainment and leisure, has resulted in "ocean sprawl" (Firthet al, 2016).

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Rapid seaward expansion of seaport footprints worldwide

“…Time series of seaport expansion -for these and the hundreds of expanding ports not included among the top-100 by throughput 2,3,4,8 -may inform and refine approaches to forecasting future expansion of coastal infrastructure 17,18 . Moreover, until recently, leading global digital elevation models were derived from Earth observation data that predated much of the seaport document we present here 19 . As new, high-resolution global datasets of coastal elevation become available 20,21 -and as analytical tools and techniques make it easier to determine elevation change from existing satellite catalogues, such as InSAR 12 -researchers will be able to more accurately and comprehensively assess patterns of coastal vulnerability to future natural hazards 10,11 .…”