How to increase the safety of 3 billion people: understanding informal settlement vulnerabilities (New Study in PNAS)
Informal settlements refer to urban districts that have developed outside state control (Kalamipour and Dovey, 2019) with unplanned urban design and un(der) regulated construction. While often being ignored socially and officially, residents of informal settlements have been estimated to number a billion globally (UN-HABITAT 2006), projected to grow to 3 billion by 2050 (UN-HABITAT, 2024). Due to their material deprivation, political marginalisation, and social fragmentation, informal settlements are highly vulnerable to natural hazards and interconnected compound risks. That is, nearly a third of the total human population could be at risk of severe natural disasters by 2050.
Informal settlements therefor must be better prepared for the natural disasters of today and the future. Yet there is a gap of both spatial coverage and vulnerability assessment of global urban informal settlements in order to target support effectively. A new study by Chen et. al. published in PNAS tackles this issue by constructing the Urban Informal Settlements Vulnerability Index (UISVI). The paper “Multidimensional vulnerabilities of informal settlements in the Urban South” describes this composite metric which was derived by using satellite imagery and applying a deep learning model on 1,914 informal settlement cities of the Global South. The metric recognises the varied ways in which informal settlements are vulnerable, since no two settlements are alike in their composition and environments.
The UISVI consists of 12 quantitative indicators spanning three dimensions: living conditions, social infrastructure, and environmental exposure. In other words, informal settlement vulnerabilities can be identified along these three vulnerability dimensions. Living Conditions Vulnerability (S1) captures quality-of-life metrics including greening level, water quality, population density, and GDP per capita. Social Infrastructure Vulnerability (S2) refers to essential services infrastructure, incorporating electricity consumption per capita, road density, healthcare access, and school access. Environmental Risk Vulnerability (S3) encompasses exposure to nitric oxide (NO₂), air quality (measured by PM2.5), susceptibility to flood risk, and heatwaves.
When looking a the median values of UISVI, Sub-Saharan Africa emerges as the most vulnerable region. South Asia (e.g. India, Pakistan), and North Africa (e.g. Egypt, Morocco) follow. Digging into the data further uncovers regional variation. While the aggregate UISVI median for Sub-Saharan Africa is highest, it ranks second in each individual vulnerability dimension (e.g. ranks second in Living Conditions Vulnerability). South Asia has the highest rank in Social Infrastructure and Environmental Risk Vulnerabilities, with rapid and low-quality urbanisation combined with heatwave and flooding risks responsible for these rankings.
As the South Asia finding demonstrates, informal settlements have different combinations of vulnerabilities. The following eight types were identified from the data by assigning a high (H) or low (L) value to each of the three vulnerability dimensions (s1, S2, S3) per city. The identification of the eight types will help in targeting better-suited solutions to improve informal settlement safety through resource prioritisation and context-sensitive planning.
High vulnerability type (HHH)
23.51% of the data were classified as high vulnerability (n=450) with disadvantages in all three dimensions. These disadvantages are thought to reflect “regional infrastructure deficits and institutional constraints”, and are concentrated in India (n = 76), Nigeria (n = 29), Iran (n = 13), Iraq (n = 11), and Egypt (n = 10). Examples:
New Delhi (India)
Lagos (Nigeria)
Tehran (Iran)
Cairo (Egypt)
Low vulnerability type (LLL)
21.26% of the data were classified as low vulnerability (n=407), demonstrating low risks across all three dimensions, “showing better structural stability, service accessibility, and environmental safety.” More than half of these cities are in China (n=217), reflecting “the effectiveness of China’s state-led infrastructure upgrades and spatial governance policies in alleviating urban poverty.”
Living conditions vulnerability type (HLL)
Informal settlements with issues in building materials and density control but with a certain level of service accessibility and environmental security. Prevalent in regions like China (n = 60), Mexico (n =4), and South Africa (n= 4). Examples:
Yinchuan (China)
Pietersburg (South Africa)
Service deficiency type (LHL)
This type is found in areas with “inadequate institutional service provision, where resources such as transportation, healthcare, and education have been persistently underprovided.” Common in countries like Brazil (n =18), Indonesia (n = 8), and Thailand (n = 5). Examples:
San José (Costa Rica)
Londrina (Brazil)
Longyan (China).
High environmental exposure type (LLH)
These informal settlements have a basic level of housing and services, but are in areas vulnerable to heatwave, flooding, and pollution. This type is predominantly found in larger cities. Examples:
Guangzhou (China),
Johannesburg (South Africa)
Kuala Lumpur (Malaysia).
Living and social vulnerability type (HHL)
Characterised by poor housing quality, overcrowding, and a lack of public services. Residents face difficulties in accessing basic guarantees such as education and healthcare. Prevalent in countries like Mexico (n = 16) and Brazil (n = 35). Examples:
Santiago (Chile)
Hanoi (Vietnam)
Favelas in São Paulo (Brazil).
Social and environment vulnerability type (LHH)
Pressured by lack of service accessibility as well as environmental risks, such as settlements located in flood-prone areas without sufficient infrastructure. Residents are exposed to risks of heavy rainfall, high temperatures, or pollution. This vulnerability type is particularly common in China (n= 12), India (n = 18), and Indonesia (n = 7). Examples:
Rio de Janeiro (Brazil)
Bandung (Indonesia)
Living and environment vulnerability type (HLH)
Informal settlements characterised poor economic conditions and simultaneous exposure to environmental risks like heatwaves, pollution, and flooding. Examples:
Accra (Ghana)
Manila (Philippines)
The authors point out that the the multidimensional vulnerabilities reflect the “systemic lack of social infrastructure and governance mechanisms” in addition to material deprivation. “Therefore, systematically improving infrastructure and governance requires treating informal settlements as integral components of cities and fully integrating them into the broader urban planning framework.” This study provides a snap-shot of informal settlement vulnerabilities at present, and the authors identify the need for tracking the changes in informal settlements overtime as climate change is forcasted to exacerbate the disadvantages and vulnerabilities. Additionally the authors call for research that investigates the diversity of social groups in informal settlements and their emotional and psychological attachments to their homes, as a way of supporting equitable urban transformation in the Global South.
M. Chen, W. Song, D. Lu, Y. Deng, C. Wang, H. Jiang, Y. Zhou, M.W. Scown, L. Chen, J. Ma, H. Zheng, & X. Bai, Multidimensional vulnerabilities of informal settlements in the Urban South, Proc. Natl. Acad. Sci. U.S.A. 123 (42) e2523034123, https://doi.org/10.1073/pnas.2523034123 (2026).
References
H. Kamalipour, K. Dovey, Mapping the visibility of informal settlements. Habitat Int. 85, 63–75 (2019).
United Nations Human Settlements Programme. (2006). State of the world's cities 2006/2007: 30 years of shaping the habitat agenda. UN-Habitat. https://unhabitat.org/state-of-the-worlds-cities-20062007
United Nations, The sustainable development goals report 2024: Goal 11, sustainable cities and communities (2024). https://unstats.un.org/sdgs/report/2024/Goal-11/. Accessed 25 September 2026.
Comments