Climate Risk and Vulnerability Assessment in Informal Settlements of the Global South: A Critical Review

Abstract

This study investigated the climatic risks and vulnerabilities of informal settlements in the Global South, as well as the extent to which these risks impact the vulnerabilities. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2009 methodology and deductive content analysis, this study critically examined 69 documents, including 28 scholarly journal articles obtained from Scopus and ScienceDirect and 41 web-based releases identified through the Google search engine and snowballing technique. Document inclusion criteria focused on the relevance to climate risks and vulnerabilities, excluding non-peer-reviewed, non-English, and unreliable sources, as well as irrelevant studies. Seven major climate risks impacting informal settlements were identified: floods (44), temperature changes (41), storms (31), sea level rise (30), drought (28), rainfall (23), and landslides (14). The primary vulnerabilities highlighted were poor housing conditions (64), health risks (50), lack of basic services (49), inadequate sanitation (41), inadequate hygiene (39), and limited access to water (38). The combination of vulnerabilities and climate risks creates considerable direct, indirect, and low-level threats to informal settlements. Despite Asia, Africa, and Latin America’s vulnerability, most studies focused on formal and developed areas. The findings highlight the critical need for climate adaptation strategies in informal settlements of the Global South to ensure the United Nations Sustainable Development Goals (SDGs) are met.

1. Introduction

The ‘Global South’ is a phrase that broadly encompasses nations in Latin America, Asia, and Africa that are generally poor and often find themselves on the periphery of political or cultural power [1]. These nations are typically labeled as developing countries (DevCs) or least developed countries (LDCs). Conversely, the ‘Global South’ is juxtaposed with the ‘Global North’, comprising largely developed countries (DCs) primarily in North America, Europe, and other parts of the world that are known for their robust economies, technological sophistication, advanced infrastructure, and political and macroeconomic stability [2]. The Global South is embroiled in a host of challenges, paramount among them being the threats posed by climate change [3]. As these nations strive towards urbanization and economic progression, they encounter unique susceptibilities to the altering climate. Factors such as their geographical positioning, which exposes them to rising sea levels and other severe weather phenomena, contribute to these susceptibilities [4].

In countries typically grouped under the Global South, diverse community setups and residential patterns exhibit varying susceptibility to climate risks [5]. Informal settlements, where more than one billion people reside and form a significant part of the communities in the Global South, are characterized by distinct vulnerabilities to climate risks due to inherent challenges and infrastructural deficiencies (Figure 1) [1,6,7]. Within the scope of this study, ‘vulnerabilities’ of informal settlements refer to inherent weaknesses or susceptibilities within the settlements, aligning with what Chambers [8] terms ‘internal vulnerabilities’. Conversely, ‘climate risks’ such as floods, temperature fluctuations, sea level rise, and other extreme weather events represent ‘external vulnerabilities’. These settlements lack secure tenure, basic services, and infrastructure, leaving their residents disproportionately exposed and at risk [9]. The vulnerabilities of informal settlements are heightened by the interplay between the Global South’s inherent challenges, specific conditions within these settlements, and the escalating climate change threats. The complex dynamic between the Global South, climate risks, and informal settlements magnifies the existing trials faced by these communities and intensifies climate change effects, resulting in a reinforcing cycle of vulnerability [3,10]. A nuanced understanding of this complex interplay is lacking to devise effective mitigation strategies and enhance living conditions.

While the relationship between the Global South, climate risks, and informal settlements’ vulnerabilities has not been extensively documented as a unified topic, the climate risks towards DCs and formal settlements around the world are well investigated. The notable absence of detailed climate risk maps for DevCs and LDCs, particularly those that focus on informal settlements, stands out even more when compared to the abundant resources available for more developed regions and formal settlements. This insufficiency of studies for informal settlements, as our study demonstrates, raises questions about climate justice (

Table 1. Climate risk maps reviewed: geographical areas, climate risks, and the gap in coverage for informal settlements in the Global South (retrieved via snowballing technique).

Geographical Area	Climate Risks	Map Link
World	Storms (hurricanes, typhoons, cyclones), floods, heatwaves, precipitation, landslides, strong wind, and wildfire	https://www.germanwatch.org/en/19777 (accessed on 19 January 2024)
	Sand and dust storm	https://www.preventionweb.net/publication/global-assessment-sand-and-dust-storms (accessed on 19 January 2024)
	Sea level rise	https://ss2.climatecentral.org/#12/40.7165/-16674.0088?show=satellite&projections=0-K14_RCP85-SLR&level=5&unit=feet&pois=hide (accessed on 19 January 2024)
	Land surface temperature	https://earthobservatory.nasa.gov/global-maps/MOD_LSTD_M (accessed on 19 January 2024)
Europe	London: flood and heat risk	https://data.london.gov.uk/dataset/climate-risk-mapping (accessed on 19 January 2024)
	Europe: wind storm	https://www.eea.europa.eu/data-and-maps/indicators/storms-2/assessment (accessed on 19 January 2024)
USA	Avalanche, coastal flood, cold wave, drought, hail, heat wave, hurricane, ice storm + earthquake	https://www.americancommunities.org/mapping-climate-risks-by-county-and-community/ (accessed on 19 January 2024)
	Heat stress
	Water stress
	Extreme rainfall
	Cyclones: hurricanes, typhoons
	Sea level rise
Australia	Extreme temperature	https://www.climatechangeinaustralia.gov.au/en/changing-climate/climate-extremes/extreme-temperature/ (accessed on 19 January 2024)
	Sydney: Riverine flooding, bushfire, surface water flooding, coastal Inundation, extreme wind	https://www.climatecouncil.org.au/resources/climate-risk-map/ (accessed on 19 January 2024)
Asia	India: Cyclone, drought, flood	https://www.ceew.in/publications/mapping-climate-change-vulnerability-index-of-india-a-district-level-assessment (accessed on 19 January 2024)
	Bangladesh: Cyclone	http://dx.doi.org/10.22617/TCS210518 (accessed on 19 January 2024)
	Nepal: Avalanches, floods, heavy rainfall, landslides	https://doi.org/10.1029/2021EO159039 (accessed on 19 January 2024)
	Tajikistan: Temperature, rainfall	https://www.adb.org/publications/climate-risk-country-profile-tajikistan (accessed on 19 January 2024)
	Taiwan: Flood	https://doi.org/10.3390/w14020207 (accessed on 19 January 2024)
	Cambodia: Temperature, precipitation	https://www.adb.org/publications/climate-risk-country-profile-cambodia (accessed on 19 January 2024)
	Indonesia: Temperature, precipitation	https://www.adb.org/publications/climate-risk-country-profile-indonesia (accessed on 19 January 2024)
Africa	Ghana: Drought and flood	https://www.preventionweb.net/knowledge-base/type-content/documents-publications (accessed on 19 January 2024)

). For instance, detailed climate change projections for formal settlements, such as in the United Kingdom, indicate that extreme weather events such as sea level rise, droughts, and heatwaves will become more frequent and intense [11]. In the US, coastal cities like Miami and New York are grappling with the growing threat of inundation due to sea level rise, with predictions of an exacerbation of this risk in the coming decades [12]. Further, climate change is anticipated to amplify air pollution in urban settings, a development that could lead to significant health consequences for city dwellers [13]. The agricultural sector, a cornerstone of both rural and urban food security, is also predicted to undergo the brunt of climate change through increased instances of extreme heat and drought [14]. While such climate risk factors and related challenges do exist in developed and formal areas worldwide and impact their settlements, the implications are often far more devastating in DevCs and LDCs, particularly in their informal settlements.

The existing academic literature acknowledges the amplified vulnerability of marginalized communities, particularly those dwelling in informal settlements within the Global South, to the multifaceted repercussions of climate change. However, this body of work often stops short of delving into specific climate risks and their corresponding level of impact on the associated vulnerabilities of these settlements [15]. In a study by Hardoy and Lankao [16], the duo probed into the influence of climate change on informal settlements across Latin America. The researchers highlighted the severe threats posed by extreme weather occurrences and rising sea levels, which significantly heighten the vulnerability of these settlements to detrimental living conditions, primarily driven by flooding and landslides. Such adverse conditions lead to a domino effect of challenges, including population displacement, property loss, and infrastructural damage. Parallel research conducted by Moser and Satterthwaite [17] provided a closer look at the vulnerabilities that informal settlements in Africa present when faced with climate change impacts. The authors underlined that these vulnerabilities are rooted primarily in resource constraints and infrastructural inadequacies. In a similar vein, the story of urbanization in Asian countries, particularly South Asia, is largely told through the narrative of informal development. Informal settlements in these regions are marked by subpar facilities and low-quality infrastructure, making them acutely vulnerable to climate-related hazards such as floods and cyclones [18]. This vulnerability was brought into stark relief by the recent flooding in Pakistan, which led to the devastation of nearly two million settlements across various regions of the country [19]. Given the infrastructural quality, along with the density and size of these communities, informal settlements also face a high degree of vulnerability to climate change-induced temperature rise [20].

Numerous studies and the maps created have examined the climate risk factors affecting formal and overall settlements in DCs of the Global North, including coastal hazards, intense precipitation, drought, and rising temperature. However, these studies have not comprehensively addressed the serious hazards that affect DevCs and LDCs in the Global South, such as floods and landslides [21,22]. Furthermore, existing studies on the impacts of climate risks on formal settlements in these regions are also limited [23]. Even though informal settlements are predominantly located in DevCs and LDCs, there is a dearth of convincing and specific research that comprehensively investigates the climate risk factors impacting the vulnerabilities of these settlements. This lack of research has resulted in inadequate planning by government and non-government agencies, thereby continuing to endanger the lives of informal settlement residents [24,25]. This gap is driven by challenges in data collection, limited accessibility, and the complexity of studying informal settlements, which often lack formal recognition and infrastructure. Research funding and policy priorities tend to favor developed areas, further marginalizing informal settlements in the Global South.

Given the identified research gap, the present study aims to bridge the existing literature divide by adapting and contextualizing extant climate risk maps and studies from formal settlements, the Global North, and explored regions to informal settlements. Specifically, this endeavor aims to identify climate risk factors contributing to climate risks for human settlements, ascertain the vulnerabilities of informal settlements towards these climate risk factors, and evaluate the impact levels of these climate risk factors on the vulnerabilities of informal settlements. By achieving these integrated objectives, the study will extract pertinent climate risk factors from existing climate risk maps and texts, weigh them appropriately, and employ tailoring techniques to contextualize them within the unique landscape of informal settlements. The resulting insights will facilitate a comprehensive understanding of the climate risk factors that could potentially exacerbate the vulnerabilities of informal settlements, thereby enabling proactive planning and mitigation measures. The study employs a deductive content analysis approach to analyze the sources and achieve these research objectives.

2. Materials and Methods

The approach taken to achieve the research objective consisted of two main stages. Firstly, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2009 methodology was employed to select appropriate websites and documents, and secondly, a content analysis was conducted on the chosen maps and texts. Although PRISMA 2009 is primarily used for systematic reviews and meta-analyses of research studies, it was used in this study to identify and screen potential climate risk maps as well as papers and other relevant documents from various sources, including the grey literature [26]. Content analysis, traditionally used to analyze texts, was also used to analyze maps in this study, as it is effective in this context [27,28]. The deductive content analysis process outlined by Elo and Kyngäs [29] was followed, which involves preparation, organization, and reporting phases, to analyze the selected documents and maps. Descriptive analysis was also used to analyze quantitative data. Overall, the methodology involved a rigorous and systematic approach to analyzing the texts and maps and deriving insights from them.

2.1. PRISMA 2009 and Selection of Resources

2.1.1. Defining Objective and Research Question

The general objective of this study was to identify and analyze the factors contributing to climate risks for human settlements, as depicted in documents and climate risk maps, and apply them to the informal settlement context. This general objective paves the way for potential hypotheses regarding the most commonly depicted climate risk factors, as well as possible geographical variations in the representation of these risks. Other information retrieved from documents and the maps included the vulnerabilities of settlements, the level of impact of climate risk factors towards settlements, the indicators and datasets used to create maps, the methodologies, the extent of the maps (both geographically and population-wise), and mitigation measures proposed to tackle the climate risks. The specific information was retrieved from scholarly journal documents (peer-reviewed papers) (Appendix A) and web-based releases (maps, reports, and policy documents) (Appendix B and Appendix C). In case there was a climate risk map in scholarly journal documents, it was sent to Appendix B and Appendix C for further investigation.

The specific research questions of the study investigated through the systematic literature review (SLR) and content analysis of texts and maps within scholarly journal documents and web-based releases are as follows:

• What are the climate risk factors contributing to climate risks for human settlements?
• What vulnerabilities do informal settlements have towards these identified climate risk factors?
• What levels of impact do these climate risk factors have on the vulnerabilities of informal settlements?

2.1.2. Defining Inclusion and Exclusion Criteria

The authors included any scholarly journal documents or web-based releases that were responding to our overall study aim and specific objectives. The resources included either focused clearly on climate risk factors, discussed human settlements’ vulnerabilities, or mentioned the impact of those climate risk factors on the vulnerabilities of human settlements (

Table 2. Inclusion and exclusion criteria.

Criteria	Inclusion	Exclusion
Publication timeline	Any	Not excluded any
Document type	Peer-reviewed papers (research and review articles), web-based maps, government and non-government reports, policy documents	Unreliable resource (Papers-not peer-reviewed, web-based maps-not government or credible organization), report and policy documents-not relevant, book, book chapters, conference proceeding, repeated
Language	English	Other than English
Nature of study	Papers, reports, policy documents and web-based releases focused on climate risk, human settlements, urban vulnerability, and climate vulnerabilities of formal or informal settlements	Not focused on climate risk, human settlements, urban vulnerability, and climate vulnerabilities of formal or informal settlements
Study area	Urban studies, climate change and climate risk, human settlements, architecture, and other relevant areas	Not related to climate risk and human settlements
Location	Any	Not excluded any

). The inclusion of sources based on fulfilling one or more criteria of the study has been previously proposed [30]. Thus, documents that addressed one or more of these key topics were included to ensure a comprehensive review of the literature. The selection process prioritized peer-reviewed journal articles, government and non-government reports, policy documents, and other credible web-based releases. Only English-language documents were included to maintain consistency in the analysis. Excluded from the review were non-peer-reviewed documents, non-English sources, unreliable materials such as unverified web-based releases, and any content not focused on the specific objectives of the study. Maps that explicitly represented climate risks for settlements or focused on any of our specific objectives were selected. Our inclusion criteria were broad to capture a wide range of maps, including those from various geographical regions and representing different types of climate risks. The authors excluded maps that did not specifically focus on climate risks or those that did not provide sufficient details for analysis. Repeated maps on the same climate risk factor from the same area were also excluded. Reviewing relevant maps was considered one of the efficient ways to achieve the first objective.

2.1.3. Search Strategy to Identify Scholarly Journal Documents and Web-Based Releases

The authors used advanced searching techniques on databases (Scopus and ScienceDirect) to retrieve scholarly journal documents, and both advanced and manual searching (handpicking technique and backward tracking) on the Google search engine to retrieve web-based releases. The authors also used the snowballing technique to identify additional resources. Although not a lot of studies have been conducted to retrieve information from web-based releases, they possess important information [31]. Cooper et al. [32] suggested diversifying the sources and searching techniques and not relying on database searching. To reduce the influence of search engine personalization, we used private browsing modes and a VPN to minimize regional bias. Our search terms broadly included climate risk factors, human settlements, and climate vulnerabilities of formal and informal settlements. The specific keywords and string used are presented in

Table 3. The tested search string used in Scopus, ScienceDirect, and Google search engines to retrieve relevant scholarly journal documents and web-based releases.

Database	Attempts	Search String	Documents Retrieved	Relevance to Study Aim	Objective 1, Climate Risk Factors	Objective 2, Settlement Vulnerabilities	Objective 3, Climate Risk Level of Impact on Settlement Vulnerabilities
Scopus	1	TITLE-ABS-KEY ((“climate change factor” OR “climate change map” OR “climate risk map”) AND (“settlement” OR “informal settlement”) AND “vulnerability”)	1	Medium	Yes	Yes	Yes
	2	TITLE-ABS-KEY ((“climate change factor” OR “climate change map” OR “climate risk map” OR “climate change impact”) AND (“settlement” OR “informal settlement”) AND (“vulnerability” OR “vulnerable”))	62	Medium	Yes	Yes	Yes
	3	TITLE-ABS-KEY ((“climate risk” OR “climate change map” OR “climate risk map” OR “climate risk impact”) AND (“settlement” OR “informal settlement”) AND (“vulnerability” OR “vulnerable”))	40	High	Yes	Yes	Yes
	4	TITLE-ABS-KEY ((“climate risk” OR “climate change map” OR “climate risk map” OR “climate risk impact” OR “climate change impact”) AND (“settlement” OR “informal settlement”) AND (“vulnerability” OR “vulnerable”))	99	High	Yes	Yes	Yes
ScienceDirect	1	((“climate change factor” OR “climate change map” OR “climate risk map”) AND (“settlement” OR “informal settlement”) AND “vulnerability”)	0	Low/none	No	No	No
	2	((“climate change factor” OR “climate change map” OR “climate risk map” OR “climate change impact”) AND (“settlement” OR “informal settlement”) AND (“vulnerability” OR “vulnerable”))	7	High	Yes	Yes	Yes
	3	((“climate risk” OR “climate change map” OR “climate risk map” OR “climate risk impact”) AND (“settlement” OR “informal settlement”) AND (“vulnerability” OR “vulnerable”))	11	High	Yes	Yes	Yes
	4	((“climate risk” OR “climate change map” OR “climate risk map” OR “climate risk impact” OR “climate change impact”) AND (“settlement” OR “informal settlement”) AND (“vulnerability” OR “vulnerable”))	17	High	Yes	Yes	Yes
Google search engine	1	((“climate risk” OR “climate change map” OR “climate risk map” OR “climate risk impact” OR “climate change impact”) AND (“settlement” OR “informal settlement”) AND (“vulnerability” OR “vulnerable”))	14	Low	Yes	Yes	Yes
	2	(“climate risk” OR “climate change map” OR “climate risk map” OR “climate risk impact” OR “climate change impact”) AND (“settlement” OR “informal settlement”) AND (“vulnerability” OR “vulnerable”)	153	Medium	Yes	Yes	Yes
	3	“climate risk”|“climate risk impact”|“climate risk map”|“climate risk impact” & “settlement”|“informal settlement” & “vulnerability”|“vulnerable”	158	High	Yes	Yes	Yes

. The authors used Boolean operators (AND, OR) to combine keywords in their advanced searching process and retrieve more relevant documents. The search was conducted on 19 January 2024.

2.1.4. Screening, Eligibility Check, and Inclusion of Resources

The initial search yielded a vast number of scholarly papers, web-based releases, and resources through snowballing (Figure 2). We followed the two-step screening process outlined in the PRISMA guidelines, first removing duplicates and irrelevant results based on their titles and short descriptions, then reviewing the remaining results in more depth to decide their relevance to the research objectives.

The distribution of scholarly journal resources screened for this study suggests a notable concentration of investigative efforts on the study’s keywords in countries of the Global North, such as the United States, United Kingdom, and Australia. The research sources timeline spans from 2000 to 2023, illustrating a broad temporal analysis. This timeline further highlights an escalating trend in research on climate risks, human settlements, and associated vulnerabilities over the last decade and a half, compared to previous periods. Furthermore, the co-occurrence of author keywords correlates with the specific aims of this study, lending validity to the search outputs from the systematic literature review. The three predominant keywords that emerged were ‘climate change’, ‘vulnerability’, and ‘adaptation’ (Figure 3). The strong interconnection between ‘climate change’ and the other two key terms, ‘vulnerability’ and ‘adaptation’, underscores the intrinsic linkage. This association further validates the premise that various climate change risks expose settlements to a spectrum of vulnerabilities, necessitating tailored adaptation strategies. ‘Adaptation’ in this context refers to the process, actions, or changes made to effectively manage the adverse impacts of climate risk factors on human settlements, particularly informal ones.

During the eligibility stage, the scholarly journal documents and web-based releases went through a more rigorous checking process where the titles, abstracts, and contents were carefully reviewed to make sure the criteria for inclusion and exclusion previously mentioned were followed and the study objectives were achieved. In this stage, a total of 61 items were excluded due to the lack of relevance to the current study or lack of details to respond to the objectives. After the screening and eligibility check, the total number of research sources was 69 (28 scholarly journal documents, 18 web-based releases, 23 resources identified through snowballing), and they were delivered to the content analysis stage.

2.2. Content Analysis and Data Extraction

After 69 records were included using the PRISMA 2009 method, the content analysis of these resources started in three steps (Figure 4), considering the specific research questions. These steps are explained as follows:

2.2.1. Preparation

To initiate the first step toward identifying climate risk factors, vulnerabilities of informal settlements, and the impact levels of these risk factors on the vulnerabilities, a comprehensive familiarization process was conducted with the selected sources. This served as the foundation for a subsequent in-depth analysis. This stage aimed to identify general patterns and extract relevant information for creating the units of analysis, such as floods, temperature, sea level rise, and other climate risk factors depicted in the maps or mentioned in other included sources that could pose a threat to settlements. Similar units of analysis were constructed for vulnerabilities of settlements towards climate risk factors. During the familiarization process, each source was meticulously reviewed to grasp its purpose, scope, and key features. Specifically, we focused on aspects such as source purpose, spatial extent, location, climate risk factors covered, and whether they provided any information to respond to the other objectives. For instance, the flood risk map for London was reviewed during the familiarization process [33]. It aimed to assess and visualize flood risks (climate risk factor unit of analysis) in different areas of the city, covering both urban and suburban regions. The map primarily focused on depicting flood risk as a climate-related hazard, providing insights into vulnerable areas and the likelihood and severity of potential flood events. Spatial analysis techniques and various data sources were utilized in the map creation. Extracted details included flood-prone locations, dataset format, and proposed mitigation measures. This familiarization process informed subsequent coding and analysis, contributing to a comprehensive examination of flood risk in settlements within London. Information lacking on other objectives was left blank. A similar process was followed for the scholarly journal documents and other text-based sources. In essence, this initial phase of the content analysis produced a preliminary and detailed coding framework (Appendix A, Appendix B and Appendix C) to guide the next stage in fulfilling the research objectives.

2.2.2. Organization

In the organizational phase, a comprehensive coding scheme was developed, drawing upon the preliminary framework generated during the preparation stage. This scheme was then rigorously tested to ensure its alignment with the research objectives. The scheme efficiently categorized the identified climate risks, vulnerabilities of settlements, and their respective levels of impact. Through an iterative process, initial listings for all objectives were meticulously assessed and refined. Ultimately, the final coding scheme was established, serving multiple objectives: it avoided overlapping units of analysis and ensured responses to the research questions. This framework was utilized to categorize data from the selected sources, specifically the preliminary data outlined in Appendix A, Appendix B and Appendix C, which had been identified in the preparatory phase. For example, the coding scheme for climate risk factors was comprehensively structured and included seven key elements: floods, temperature change, rainfall, storms, sea level rise, landslides, and drought. These units of analysis were able to encompass all climate risk factors mentioned in the sources. This phase thus generated both sufficient and reliable data for the ensuing analysis.

Figure 4. Flow of the deductive content analysis of sources. (Inspired by Elo and Kyngäs [29]; Lee [34]).

Figure 4. Flow of the deductive content analysis of sources. (Inspired by Elo and Kyngäs [29]; Lee [34]).

2.2.3. Reporting

After applying the coding scheme to all sources, the findings were systematically analyzed to identify key patterns and trends. To ensure scientific rigor, inter-rater reliability was confirmed with a second coder, thereby validating the categorization and affirming the internal validity of the study [34]. Through the descriptive analysis conducted as part of the third stage of the content analysis, significant patterns were reported. For instance, it was observed that a large number of the sources focused on the factors of floods and temperature change. Other trends such as regions at risk of a specific climate risk factor emerged. These systematic analyses allowed for the application of results to the context of informal settlements. Trends regarding the vulnerabilities of settlements towards climate risks and the level of impacts towards the vulnerabilities were also reported.

3. Results and Discussion

3.1. The Research Gap: Climate Risks for Informal Settlements

The existing body of research concerning the effects of climate change on human habitation, while extensive, leaves a significant knowledge void in understanding the climate risk factors that amplify climate risks for human settlements, especially informal ones in the Global South. Regrettably, current research and available mapping resources are often skewed toward DCs and formal settlements, thereby marginalizing the unique vulnerabilities of those in informal settlements [35]. The absence of focused research on these settlements is particularly unsettling, as these communities are often situated in hazard-prone areas and lack sturdy infrastructure, making them more vulnerable to climate change impacts [36]. Furthermore, the exclusion of these communities from climate-centric research and policy conversations hampers our comprehension of their distinctive vulnerabilities.

To address this knowledge gap, this study aligns its objectives with the well-known environmental risk assessment framework, the Crichton Risk Triangle. Specifically, the study focuses on three key aspects: hazards, which are external climate risk factors; vulnerability, which pertains to the unique vulnerabilities of informal settlements; and exposure, which measures the impact level of these external climate risk factors on the vulnerabilities [37]. By aligning the study objectives with this established framework, the review aims to contribute to the formulation of bespoke adaptation strategies and risk reduction measures that cater to the unique needs of informal settlements in the Global South. This alignment not only facilitates a nuanced understanding of the risks but also lays a foundation for future research and policy interventions. By addressing any facet of the triangle—whether it is hazards, as represented by climate risk factors, vulnerabilities of informal settlements, or exposure, regarded as the levels of impact—the overall climate risk can be effectively reduced. Ensuring these often-overlooked communities are adequately represented in our fight against climate change is crucial as we work towards mitigating the varied consequences of this global crisis.

3.2. Content Analysis of the Sources for Climate Risks, Vulnerabilities of Informal Settlements, and Climate Risk Impact on the Vulnerabilities

The study performed a content analysis on a total of 69 documents, consisting of 28 scholarly journal articles obtained from Scopus and ScienceDirect, and 41 web-based releases identified through Google search and snowballing (Appendix A and Appendix B). The data gleaned from the academic articles encompassed several facets including, but not limited to, the geographical focus of the study, the region of the world (Global North or Global South), the type of settlements (formal or informal), the presence of a climate risk map, and the discussion of climate risk factors. Moreover, the authors also evaluated the vulnerabilities of the settlements under study, the level of impact of climate risk factors on these vulnerabilities, and any potential mitigation strategies proposed within these sources. The resources identified through the Google search and the snowballing approach were subject to a more focused analysis, given that a significant proportion of these materials contained maps. Consequently, the authors extracted additional data such as the types of maps, data format, and methodologies used to create these maps, as well as the scale of analysis (both area-wise and population-wise). The procedure of information procurement and subsequent analysis applied to academic articles and web-based content, inclusive of map data, is in line with the methodology delineated by other studies [27,38].

3.2.1. Descriptive Analysis

Building on the content analysis, a descriptive analysis was conducted to gain a deeper understanding of the geographical distribution of the records included in the current study. The analysis revealed notable patterns (Figure 5). Despite the Global North being represented by eight unique entities in the dataset, a significant portion of the documents were focused on just two countries within it: the USA and Australia. Together, these two countries were the focus of 11 studies, suggesting a concentrated research interest. In contrast, the Global South, despite having a larger representation in terms of unique entities, exhibited a dispersed focus with fewer studies dedicated to individual countries. This highlights a critical research gap. While studies on climate risks in the Global North (DCs and formal settlements) tend to focus on specific countries, research on the Global South (DevCs and LDCs) is less concentrated, leading to the potential neglect of country-specific risks and vulnerabilities [14]. This research concentration mirrors the findings of Klingelhöfer et al. [39], who noted the robust research infrastructure and the depth of climate change research in the Global North, as compared to the Global South. In addition to the geographical difference, the descriptive analysis also underscores a significant imbalance in the focus on settlement types in the examined documents. Most countries and regions tend to revolve their focus around settlements classified as “General” (incorporating both formal and informal) (n = 16; 57.1%) or formal settlements (n = 8; 28.6%). In contrast, the attention given to informal settlements appears markedly less (n = 4; 14.3%). This discrepancy illuminates the relative neglect of informal settlements, concentrated in the Global South, in climate risk studies [9,40]. Importantly, this neglect in investigations further extends to household-level attributes within informal settlements, which can be key causative agents of differential vulnerabilities. The scope of these rarely studied household-level vulnerabilities within informal settlements may encompass environmental aspects (sensitivity to environmental impacts), economic conditions, social factors, disease susceptibility (protective functions of households), and vulnerabilities related to the labor force (affecting productive functions) [41].

3.2.2. Climate Risk Factors, Vulnerabilities, and Impact Level

During the preparation stage of the content analysis focused on the study objectives, the authors reviewed the included sources and identified seven units of analysis related to climate risk factors: flood, temperature change, rainfall, storms, sea level rise, landslides, and drought. In the organization stage, the authors modified the terms of these factors and proposed a coding scheme for data analysis, considering previous studies such as [21,22]. However, the coding scheme used in the current study is more comprehensive than those used in previous studies. For example, while [21] identified rising temperatures as a key climate hazard, it did not include cold waves, which can also have a severe impact. The current study proposed a more inclusive code, ‘temperature change’, to encompass both rising and dropping temperatures. This decision was made to better identify the factors contributing to climate risk for human settlements. Subsequently, the sources used for the current review were coded to identify climate risk factors (

Table 4. Climate risk factors and vulnerabilities of settlements mentioned by the sources.

Sources	Climate Risk Factors							Vulnerabilities of Settlements
	Floods	Temperature Change	Rainfall	Storms	Sea Level Rise	Landslides	Drought	Inadequate Sanitation	Inadequate Hygiene	Limited Access to Water	Poor Housing Conditions	Health Risks	Lack of other Basic Services
[43]		✔	✔								✔	✔	✔
[44]	✔						✔	✔	✔	✔	✔	✔	✔
[45]						✔		✔	✔		✔	✔	✔
[46]	✔										✔	✔
[47]	✔	✔	✔	✔		✔					✔	✔	✔
[48]	✔							✔	✔	✔	✔	✔	✔
[49]		✔	✔	✔	✔	✔		✔	✔	✔	✔		✔
[50]	✔					✔	✔	✔	✔	✔
[51]	✔			✔	✔			✔	✔		✔	✔	✔
[52]	✔	✔		✔	✔		✔			✔			✔
[53]	✔										✔		✔
[41]		✔	✔								✔		✔
[54]	✔	✔	✔				✔				✔		✔
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[102]	✔	✔	✔	✔	✔			✔	✔	✔	✔	✔	✔

✔ Climate risk factor or vulnerability mentioned by the source.

). Although some sources featured more specific factors than the seven proposed in the coding scheme, these factors were able to be accommodated under the proposed scheme (

Table 5. Climate risk factors and vulnerabilities of settlements towards climate risks synthesis.

Climate Risk Factors Synthesis					Vulnerabilities of Settlements Synthesis
Factors	Specific factors/terms described in the sources	Number of times a factor is investigated in sources	Countries/regions most vulnerable to the climate risk factor	Most vulnerable countries to climate risks	Vulnerabilities	Specific vulnerabilities/terms described in the sources	Number of times a vulnerability is investigated in sources
Floods	Flood, flood risks, riverine flooding, surface water flooding, coastal floods, coastal inundation	44	South Asia and Sub-Saharan Africa [103]	Mozambique, Zimbabwe, Bahamas, Japan, Malawi, Afghanistan, India, South Sudan, Niger, Bolivia, Sudan, Nepal, Bangladesh, Indonesia, Pakistan, Comoros, Philippines, Iran, Australia, Paraguay [72]	Inadequate sanitation	Inadequate sanitation, lack of proper sanitation, unsafe waste disposal, sanitation	41
Temperature change	heat risk, heat stress, heat wave, temperature, extreme temperature, heat extreme, land surface temperature, cold wave, wildfire, bushfire, urban heat islands	41	Small island developing states (SIDS), Arctic and high-mountain regions, Africa, Asia, particularly Southeast Asia and South Asia, Latin America [104]		Inadequate hygiene	Inadequate hygiene, individual hygiene, hygiene	39
Rainfall	Extreme rainfall, heavy rainfall, precipitation	23	South and Southeast Asia, Central and East Africa, Caribbean islands, South America [105]		Limited access to water	Limited access to water, water shortage, drought, lack of water, water unavailability	38
Storms	Typhoons, hurricanes, cyclones, tropical cyclones, sand and dust storms, windstorm, ice storm, avalanches, strong wind, extreme wind, hail, storm surges	31	Coastal areas of Europe, North America, Caribbean islands, Southeast Asia, India, Bangladesh, East Africa, Middle East and North Africa for sand and dust storms [106]		Poor housing conditions	Poor housing conditions, poor infrastructure of settlements, inadequate and substandard housing structures, increasing health, safety, financial, and shelter concerns	64
Sea level rise	Sea level rise	30	SIDS, Coasts of Bangladesh, India, Africa, U.S, Southeast Asia, Caribbean islands [107]		Health risks	Health risks, diseases, health issues, injuries, losses	50
Landslides	Landslides, slope instability, mudslides	14	Nepal, Himalayan region, the Philippines, Central America, East Africa [72]		Lack of other basic services	Lack of other basic services, limited access to healthcare, education, transportation, mobility, economic services, other infrastructure	49
Drought	Drought, water stress	28	Sahel region, horn, and south of Africa, central and south America, south and central Asia, Australia [108]

). It is worth noting that some sources displayed more than one factor simultaneously. In addition, six units of analysis were found in the preparation stage of the sources for vulnerabilities of settlements towards climate risks, and the data for them were organized and retrieved like the first objective. For instance, the ‘poor housing conditions’ unit of analysis evolved to include several vulnerabilities, encompassing housing-related differential vulnerabilities in various contexts, ranging from financial to standard-related issues in housing. This approach resonates with the findings of Pandey et al. [42], who extensively investigated differential vulnerabilities in informal settlements within the Indian context. Their study highlighted that the vulnerability of urban slum dwellers in Dehradun, located in the Indian Himalayas, is intrinsically linked to household-level resources and decision-making capacities. These factors are critical in determining the overall vulnerability and adaptive capacity of these communities to climate change impacts. However, the specific vulnerabilities identified by Pandey et al. [42] were highly context-specific and presented challenges in their application to broader planning contexts in the Global South. Acknowledging this, the current study’s categorization of units of analysis for vulnerabilities incorporates a more holistic perspective, considering both the socio-ecological dimensions of slums and the household-level capability and capacity factors. This comprehensive approach aims to create a categorization that is not only inclusive of various dimensions of vulnerability but also practical and adaptable for planning and mitigation strategies in diverse settings.

The content analysis revealed a distinct pattern regarding the frequency of mentioned climate risk factors in the literature. Flood emerged as the most frequently cited risk (mentioned in 44 sources), followed closely by temperature change (41 sources). Storms (31 sources), sea level rise (30 sources), drought (28 sources), rainfall (23 sources), and landslides (14 sources) were also identified as critical factors affecting settlements, particularly in the Global South. This is crucial, as informal settlements in these regions are often located in areas prone to these hazards, exacerbating their vulnerability (Figure 6). In terms of vulnerabilities, the analysis categorized several key areas affecting human settlements. Poor housing conditions, highlighted in 64 sources, emerged as the most significant vulnerability for informal settlements. This prominence underscores the multifaceted nature of holistic housing conditions, which include physical robustness, economic affordability, health, and psychological well-being, all of which are crucial in mitigating climate risks [109]. The predominance of ‘poor housing conditions’ as a key vulnerability can also be attributed to its intricate connection with broader household-level vulnerability factors, specifically sensitivity and adaptive capacity, as discussed by Szagri et al. [110]. ‘Poor housing conditions’ was followed by health risks (50 sources), illustrating the direct impact of climate hazards on public health. The lack of other basic services, including mobility, economic services, and infrastructure, was cited in 49 sources, indicating the multifaceted nature of vulnerabilities in these communities. Inadequate sanitation (41 sources), hygiene (39 sources), and limited access to water (38 sources) were also significant concerns. These vulnerabilities are particularly acute in informal settlements of the Global South, which frequently face these hazards due to their geographical positioning and infrastructural deficits [104,105]. The data indicate that all seven identified climate risk factors pose substantial threats to these communities, necessitating targeted and effective mitigation strategies.

The most vulnerable countries and settlements to flood risks in the third decade of the 21st century are located in South Asia and Sub-Saharan Africa, while those in Europe and North America have demonstrated a decreased susceptibility to flooding. Bangladesh, in South Asia, is the most vulnerable, with an estimated 27 million people exposed to the climate risk factor of flooding. Among the various negative impacts, floods have been reported to cause significant health issues, including severe depression, affecting over half of the women in these regions [111]. Additionally, in these flood-prone settlements, while overall calorie intake could be maintained during a flood, the diversity of diet decreases due to lower per capita food expenditures [112]. Furthermore, it is estimated that 86 million more people have settled in areas at risk of flooding, representing a 24% increase in the population exposed to floods [103]. These high-risk areas include informal settlements that are predominantly located in these countries [113]. However, there has been a lack of research on flood risks in informal settlements and their residents in South Asia and Africa. While a large number of the reviewed sources indicated elevated flood risks in these regions, they did not provide precise information on specific high-risk areas, such as informal settlements, nor did they highlight the particular vulnerabilities that these areas have to floods. With approximately 30% of the population living in informal settlements, these DevCs and LDCs and their settlements are at a higher risk of experiencing the adverse effects of flooding [114].

One of the most significant factors in climate change, according to the current review, is temperature change, with a significant number of analyzed sources focusing on this factor. Pachauri et al. [104] identified several high-risk areas, including island states, Arctic and high-mountain regions, Africa, Asia (particularly Southeast and South Asia), and Latin America, that are currently being affected by climate change and will continue to be in the future. This suggests that temperature change is a global phenomenon that is affecting people in almost all parts of the world, as stated by the IPCC [14]. The reviewed world map reveals higher surface temperatures in many Asian and African countries, where most informal settlements lack social, financial, and infrastructural preparedness against temperature changes, making this climate risk factor particularly dangerous for these regions [84]. Crucially, within these informal settlements, differential vulnerabilities at the household-level are a significant concern. A study by Carter et al. [115] emphasized that each household’s unique composition, resource availability, and decision-making capacities contribute to varying levels of sensitivity and adaptive capacity to climate risks. For example, households with limited financial resources or inadequate access to climate adaptation facilities are disproportionately impacted by extreme temperatures, a condition explored in depth by Lanza et al. [116]. Moreover, the psychological impacts of such climate risks, including mental disorders and even suicide and violence, are crucial factors in household vulnerability, as shown in the studies by Lowe et al. [117] and Lee et al. [118]. This highlights the necessity for climate adaptation strategies that are both community-focused and tailored to meet the specific needs and vulnerabilities at the household level within informal settlements, a point underscored by the work of Thomas et al. [119] on localized climate resilience.

Storms, particularly those that occur along coastlines, are a major contributor to climate risks facing human settlements. Coastal countries in the Americas, Europe (particularly the United Kingdom), Southeast Asia, Bangladesh, India, Africa (including Egypt, Mozambique, and Nigeria), and other vulnerable regions are at risk of experiencing severe damage due to storms. One example of the destructive power of coastal storms is Hurricane Sandy, which caused nearly USD 70 billion worth of damage to settlements and infrastructure [12]. Families often face not only the immediate physical damage but also the long-term consequences of recovery and rebuilding houses in poor conditions [120]. Without robust structures to withstand such events, these households can experience disproportionate economic burdens, loss of personal belongings, and disruptions to daily life and livelihood. Moreover, the psychological stress caused by storms can lead to long-term mental health challenges, compounding the adversity faced by these communities [121]. Additionally, rising sea levels pose a significant threat to countries with vulnerable infrastructure, particularly in South Asia [70]. The gradual loss of land and increased susceptibility to floods caused by sea level rise not only displace communities but also diminish local economic opportunities, leading to broader socioeconomic instability. Health risks, ranging from physical to mental, associated with sea level rise need supplementary attention when it comes to highly prone informal settlements [122,123,124]. Drought is another climate risk factor that disproportionately affects individuals living in DevCs and LDCs. Informal settlement residents are particularly vulnerable, as they lack access to piped water systems and other necessary facilities [25]. Drought can lead to price increases that low-income residents cannot afford, resulting in a decline in their settlement’s standard of living and increased vulnerability to other risks [125].

Climate change has led to uneven rainfall patterns, which is another important factor in climate risk. The current content analysis notes that extreme rainfall caused over USD 2.5 billion in damages in some parts of the United States in March 2020 [126]. However, some regions have become more vulnerable to this risk, including South and Southeast Asia, Central and East Africa, the Caribbean islands, and South America. Residents in these areas not only suffer monetary losses but also human losses, as they are often ill-prepared for extreme rainfall events. For example, recent floods that covered over half of Pakistan’s territory affected around 33 million people and damaged nearly 2 million settlements [19]. Other South Asian countries, such as Afghanistan, are also facing similar consequences of extreme rainfall events. These countries have at least one thing in common: informal settlements, which are particularly vulnerable to climate risks. It is important to note that while all informal settlements are prone to the dangers of rainfall, the extent of vulnerability among residents can vary significantly. Socioeconomic status, access to essential resources, and the quality of housing are among the factors that can greatly influence the level of risk faced by individual households [127]. Landslides also pose a risk to individuals living in low-cost areas of informal settlements, particularly in hilly or mountainous regions. Due to heightened rainfall and flooding caused by climate change, along with an absence of early alert mechanisms, residents of unprepared settlements face greater risks, including the loss of homes, livelihoods, and potentially lives [72]. The consequences of these disasters often extend beyond the initial event, as recovery efforts are hindered by challenges in accessing the affected areas. This can lead to prolonged physical, psychological, social, and economic hardships for those living in informal settlements [128,129]. Recent estimates on informal settlements found that nearly 5000 people die of landslides and around USD 20 billion of losses to these low-income regions are incurred every year. The estimate also found that 80% of the landslides that occur in the tropics are fatal [130].

The interplay between climate risks identified in this study and the vulnerabilities inherent in settlements, particularly informal ones, represents a complex and intricate dynamic. The relationship becomes more complex when climate risks are discussed with the household-level differential vulnerabilities. Informal settlements, characterized by vulnerabilities such as inadequate sanitation and hygiene, limited access to water, poor housing conditions, health risks, and a lack of basic services, are particularly vulnerable to a range of hazards [130,131,132]. As per the findings of the current review, climate risks can influence these vulnerabilities through various pathways, encompassing direct (damage to infrastructure, loss of life, or injury), indirect (secondary impacts, such as reduced access to resources), and low-impact effects (less immediate impacts, such as minor damage to property or temporary disruptions to services) (

Table 6. Summary of vulnerabilities of informal settlements and exacerbating impacts of climate risk factors.

	Vulnerabilities	Inadequate Sanitation	Inadequate Hygiene	Limited Access to Water	Poor Housing Conditions	Health Risks	Lack of Other Basic Services
Factors
Floods		Direct impact	Direct impact	Direct impact	Direct impact	Direct impact	Direct impact
Temperature change		Indirect impact	Indirect impact	Low impact	Low impact	Indirect impact	Low impact
Rainfall		Direct impact	Direct impact	Direct impact	Indirect impact	Direct impact	Indirect impact
Storms		Direct impact	Direct impact	Direct impact	Direct impact	Direct impact	Direct impact
Sea level rise		Direct impact	Direct impact	Low impact	Indirect impact	Indirect impact	Low impact
Landslides		Indirect impact	Indirect impact	Indirect impact	Direct impact	Indirect impact	Indirect impact
Drought		Low impact	Indirect impact	Direct impact	Low impact	Indirect impact	Indirect impact

and Figure 7). For instance, the occurrence of floods can directly amplify all vulnerabilities, while the impact of temperature may not manifest directly, yet it can significantly contribute to indirect consequences related to sanitation, hygiene, and health risks [20]. Furthermore, temperature variations can also catalyze the emergence or exacerbation of other climate risks, further compounding the vulnerabilities experienced by informal settlements [133]. Recognizing the intricate interconnectedness of these factors is crucial, as the significance of climate risks on informal settlements may fluctuate depending on their contribution to the creation or exacerbation of other risks [133]. Addressing this multifaceted relationship necessitates a comprehensive and holistic approach, one that tackles the complex interplay between climate risks and the vulnerabilities of informal settlements, while concurrently fostering resilience and sustainable development within these communities. In the current context, ‘resilience’ is defined as the adaptive capacity of informal settlements to anticipate, prepare for, respond to, and recover from adverse climate events. This capacity encompasses social, economic, and physical dimensions and is central to mitigating the complex vulnerabilities identified.

The intricate web of climate risks and inherent vulnerabilities in informal settlements exacerbates their delicate conditions, particularly in the developing world. For instance, Afghanistan grappled with escalated temperatures and drought during the sweltering summer of 2018, intensifying water scarcity, a direct impact that strained the already deficient water supplies in informal settlements [134]. On the other hand, the indirect effects of these climate risks manifested in the form of heat-related illnesses among the vulnerable population [135]. Meanwhile, in Nepal, heavy rainfall triggered landslides and flooding, presenting direct impacts such as damaging settlements followed by displacement, and indirect impacts including the disruption of sanitation facilities and ensuing public health crises in informal communities [136]. In Bangladesh’s capital, Dhaka, a consistent influx of climate refugees due to sea level rise has led to an increased population density in informal settlements. This has not only strained sanitation and hygiene services but also created indirect yet persistent stressors such as overcrowding and heightened disease transmission [137]. In Nigeria, erratic rainfall patterns have led to recurrent flooding in informal settlements, exacerbating poor housing conditions and straining basic services, which have direct impacts such as damage to property and disease outbreaks [138]. While these challenges are common across Asia, Africa, and Latin America, each region faces unique threats; for instance, African nations like Nigeria are more vulnerable to drought and extreme heat, while Latin American countries, particularly in the Caribbean, frequently contend with hurricanes and landslides. On the other hand, South Asian countries like Afghanistan and Pakistan, with massive informal settlements, are mostly vulnerable not just to floods but to temperature change as well, considering their poor household conditions and other vulnerabilities. Despite these differences, the common thread of poor infrastructure and living conditions exacerbates the impacts of these climate risks across all three regions.

Addressing these multifaceted adversities requires comprehensive, context-specific strategies. In Afghanistan, initiatives like USAID’s sustainable water use program offer respite by addressing the direct impacts of climate risks [139]. However, the present study underscores the necessity for further measures. Key amongst these is the adept management of underground water resources, efficient water reuse and recycling systems, the establishment of climate risk-focused adaptation funding, and the introduction of drought-resistant green space cover. Each of these steps is integral to fortifying the resilience of informal settlements against drought and associated climatic threats. Other successful community-based adaptation measures in Lusaka, Zambia, have demonstrated how early warning systems and infrastructure improvements can reduce flood vulnerability in informal settlements. Similarly, in Bangladesh, coastal protection policies and sustainable urban development strategies have been instrumental in managing the challenges posed by sea level rise. While initiatives have been launched to mitigate climate hazards like landslides in Nepal, the efficacy of these efforts within the framework of informal settlements has been less than optimal [140]. As per the present research, we advocate for the development and enactment of climate-resilient infrastructure and stringent building codes. Moreover, fortifying community resilience, refining infrastructure, and service provisions, augmenting governance, and institutional capacity, as well as incorporating nature-based solutions, are recommended pathways for diminishing the vulnerability of informal settlements to climate risks. Coastal protection, improving and elevating buildings and infrastructure, managed retreat, green infrastructure, flood insurance, and risk communications are some essential measures to tackle the threat of sea level rise and floods facing informal settlements in DevCs and LDCs. Resilience among the communities is reinforced by these targeted adaption strategies, which also align closely with the Sustainable Development Goals (SDGs) of the UN. To safeguard livelihoods and reduce poverty associated with disasters, for example, better infrastructure and efficient flood management could directly contribute to SDG 1 (no poverty). As with SDGs 3 (good health and well-being) and 6 (clean water and sanitation), the supply of clean water and climate-resilient healthcare contribute to their achievement. In order to ensure that even the most marginalized communities in informal settlements do not fall behind in global sustainability efforts, we can achieve SDG 11 (sustainable cities and communities) by putting these adaptation techniques into practice.

3.3. Addressing the Gap: Adapting Climate Risk Findings to Informal Settlements

The primary objective of this study was to identify climate risk factors that contribute to the vulnerability of informal settlements. This objective was pursued through a thorough review and analysis of the literature and documents detailing climate risks associated with both formal and informal settlements. These climate risks faced by general settlements (formal and informal) and their vulnerabilities can be customized to the specific context of informal settlements as well. The nature of the impacts that climate risks have on the vulnerabilities of general settlements can also be accommodated from the informal settlements’ perspective. Thus, the results can be tailored to the specific context of informal settlements (Figure 8). The findings revealed a series of critical climate risk factors impacting human settlements, including those informal in nature, particularly in the Global South. These include floods, temperature change, storms, sea level rise, drought, rainfall, and landslides [141,142]. These results also highlighted the importance of these climate risk factors and the varying degrees to which they exacerbate the vulnerabilities of informal settlements.

In addressing the notable research void, this study astutely navigates and reinterprets the climate risk findings from formal and overarching settlements, tailoring them to the distinct dynamics of informal settlements. Most existing climate risk research casts its lens primarily on formal or general settlements, often within developed nations. However, the vulnerabilities and threats looming over informal settlements, especially in the Global South and the world’s least-developed regions, warrant specialized scrutiny [15,143]. By contextualizing and integrating these climate risk factors, the vulnerabilities, and the nature of impacts, this research enriches our holistic comprehension of the challenges that shadow informal settlements. The nuanced understandings derived from this endeavor can equip policymakers, urban strategists, and field experts with the knowledge to craft bespoke resilience-building strategies against the backdrop of climate change. By spotlighting the unique climate adversities and vulnerabilities confronting informal settlements, key stakeholders are better positioned to prioritize these often-overlooked communities, spearheading sustainable and inclusive climate adaptation initiatives. Although the findings of the current study help fill the gap and respond to the research objectives, the study is still limited by the insufficient research on informal settlements, as existing assessments often overlook these communities’ unique vulnerabilities. This underrepresentation highlights the need for focused studies to develop effective, context-specific adaptation strategies.

The additional information provided in Appendix A and Appendix B, which included evidence such as layers for analysis, dataset formats, methodologies, and mitigation measures, was critical in properly identifying climate risk factors, vulnerabilities, and impact levels and adapting existing studies to the context of informal settlements. In identifying the seven major climate risks, the methodologies from the original studies, as outlined in Appendix B, were carefully considered. These studies employed a variety of techniques, including spatial analysis using GIS, climate modeling, and statistical methods such as regression analysis and multi-criteria decision analysis. For example, studies on flood risk utilized remote sensing and digital elevation modeling, while those on temperature change applied trend analysis and climate scenario modeling. By synthesizing these diverse methodologies, the current study ensures a comprehensive understanding of the climate risks impacting informal settlements. Additionally, key vulnerabilities such as poor housing conditions and health risks were quantified using region-specific indicators. Poor housing was assessed by factors like inadequate infrastructure, lack of basic services, and building material quality, while health risks were evaluated based on the prevalence of climate-sensitive diseases and healthcare access. These indicators were standardized and compared across regions, such as the direct impact of floods on health in Lusaka, Zambia, and the exacerbation of chronic diseases due to temperature change in informal settlements in low- and middle-income countries. Spatial analysis tools, including GIS, were used to visualize and compare these vulnerabilities geographically, ensuring a thorough evaluation. Decision-makers can use this information to gain a more comprehensive understanding of the climate risk factors and develop effective strategies to address the vulnerabilities of informal settlements.

4. Conclusions

The current study identified and adeptly tailored climate risk factors, vulnerabilities intrinsic to settlements, and the consequential impact levels of these factors on stated vulnerabilities, specifically within the framework of informal settlements. The most significant climate risk factors identified were floods, temperature change, and storms. Factors investigated least, for instance, rainfall, were also considered important as they could result in the creation of other climate risks. Poor housing conditions, health risks, and lack of other services were considered the most significant vulnerabilities of informal settlements that could be impacted at different levels by climate risk factors. Even limited access to water, which is least investigated, is also an important vulnerability for informal settlements that could be exacerbated by climate risks. Additionally, the study found that countries and their informal settlements in Asia, Africa, and Latin America are the most vulnerable to these climate risk factors. However, the available sources and maps tend to focus more on DCs and formal settlements.

Based on the findings, it is recommended that governments, policymakers, and organizations pay more attention to the climate risk factors, particularly floods, temperature change, and storms, that inflict direct and significant impacts on vulnerable groups like those living in informal settlements. It is essential to devise targeted adaptation and mitigation plans to enhance adaptive capacities by improving the physical and environmental aspects of settlements and promoting climate risk awareness. This will align with the Sustainable Development Goal of building resilient urban communities in the Global South. Moreover, these adaptation strategies should be integrated into local, national, and international policies to effectively address the identified risks. Local policies should focus on community-based adaptation, while national and international efforts should prioritize resource allocation and the transfer of technology and funding to support these initiatives. Regional and local climate risk maps can help identify high-risk areas within cities and informal settlements. Better planning and design for informal settlements could reduce these climate risks. More granular data on the vulnerabilities, particularly household-level differential vulnerabilities, and impacts of climate risk factors such as flooding, temperature, and rainfall changes within informal settlements are needed. Eventually, participatory approaches engaging residents of informal settlements should be utilized to gain a better understanding of climate risks and adaptation priorities from their perspectives.

This research filled a critical gap in the study of climate risk, particularly in the context of informal settlements, and went well beyond academic circles, offering crucial insights to a global audience. It is extremely significant for a wide range of professions, including legislators, urban planners, and climate change experts, because it highlights particular vulnerabilities at the local level. Additionally, the study holds significant relevance for over 1 billion residents of informal settlements, providing them with vital knowledge about their specific vulnerabilities and the climate risks they face. Moreover, the SLR also pointed out practical solutions based on the vulnerabilities and impact level of climate risks that support both global climate policy and Sustainable Development Goals—particularly those concerning climate initiatives and sustainable urban communities. The study emphasized how important it is to know the climate risks and vulnerabilities first and then propose equitable, inclusive, and context-specific measures for mitigating those risks.

5. Limitations and Future Research

The current study admits certain limitations while being comprehensive in its attempt to identify and classify vulnerabilities and climate risk variables unique to informal settlements. Primarily, the underexplored nature of informal settlements presents a challenge in comprehensively discussing household-level capacities to tackle climate risks and their differential vulnerabilities. The existing literature often lacks detailed information on these aspects, which can sometimes lead to misunderstandings or oversimplifications in the analysis of climate risks and vulnerabilities within these communities. Furthermore, the heterogeneous character of informal settlements, encompassing various forms of informal housing, presents an obstacle in classifying and comprehending the distinct vulnerabilities at the household level. This variation might range greatly between contexts and geographical areas, making the task of creating a global framework for vulnerability assessment more difficult. Although the study aimed to create a comprehensive categorization of climate risks, vulnerabilities, and their impacts, it was constrained by its specific objectives as outlined in the methodology section. As a result, certain aspects, such as the detailed exploration of household-level differential vulnerabilities, including the socioeconomic status of women and children in informal settlements in regions like Afghanistan, were not extensively covered. This limitation was partly due to the scope and length constraints of the study, which focused on broader climate risk factors and vulnerabilities rather than delving deeply into specific demographic aspects within these settlements.

Despite offering valuable insights into climate risks and vulnerabilities in informal settlements, the study acknowledges the need for further research into specific household-level vulnerabilities and their interactions with broader climate risks. This would improve scientific knowledge and make it possible to create more focused and efficient strategies for these vulnerable groups’ adaptation to and reduction of climate risk. Future research could also explore each climate risk threatening informal settlements and aim to devise practical solutions to mitigate their effects. Furthermore, in order to fully understand the distinct vulnerabilities and adaptive skills of these communities, future research should concentrate on more local studies conducted inside informal settlements. In order to examine the long-term effects of climate risks on informal settlements and gain a better understanding of how these risks change over time and how people adjust, longitudinal studies could be very beneficial. These may contribute to closing the gaps in the existing literature, especially in unexplored regions, and offer a more precise framework for creating focused interventions and policies. The scope of the systematic review, which mostly made use of databases like Scopus, ScienceDirect, and the Google search engine, is another limitation of this study. To give a more thorough evaluation of the literature, future studies could benefit from including a wider range of databases, such as Wiley, Taylor & Francis, and others. This diversification of sources may provide fresh viewpoints and insights into the threats posed by climate change and the vulnerabilities that informal settlements face. Regarding methodologies, while the PRISMA approach offered a systematic framework for identifying and selecting relevant studies, it is not without limitations. The process may have introduced publication bias, as studies published in high-impact journals could be overrepresented, and non-English or unpublished studies may have been excluded. Furthermore, the deductive content analysis, though structured, is inherently subject to researchers’ interpretation, which could introduce subjectivity. These limitations underscore potential gaps in the literature review process and suggest the need for future research to incorporate a wider range of data sources and consider alternative analysis techniques to mitigate bias.