At any time, some households are experiencing welfare gains and moving out of poverty, whilst others are experiencing setbacks and falling into poverty1. Poverty reduction, and development more broadly, requires both advancing welfare and protecting households from setbacks. Climate-related hazards are one major cause of setbacks increasing in frequency and intensity with climate change2,3. Not only do they increase poverty when they occur, they cast a long shadow on welfare, as they can result in losses to assets, health and natural capital that limit welfare gains for many years to come. Vulnerable households are sometimes forced to adopt costly coping strategies, such as reducing spending on health and education, or selling productive assets, which can affect people’s – and especially children’s – prospects for decades4.
Sustainable development and poverty reduction requires reducing the number of people who are at risk from extreme weather events. Tracking global progress on this metric demands an indicator that can be measured consistently across countries and over time. Existing approaches to measure climate risk or vulnerability typically model aggregate economic losses or aggregate country level metrics in an index5,6,7,8,9,10. Instead, we use a granular approach to count people at high risk11, similar to what is done to monitor global poverty (the number of people living on less than $2.15 per day and the number of people multidimensionally poor). This new indicator is now being used by the World Bank as one measure of progress towards ending poverty on a livable planet [1]. It will be regularly updated and publicly available.
In this study, we present the indicator methodology and estimate the number of people at high risk from climate-related hazards globally around 2021, and its trend since 2010. We follow the traditional framework in which risk is the combination of hazard, exposure, and vulnerability12. Hazard is the potential occurrence of an extreme event; exposure is the presence of people in places or settings that could be adversely affected; and vulnerability is the propensity or predisposition of these people to be adversely affected when an extreme event occurs.
Everybody faces some level of risk from extreme weather events, and everyone is vulnerable to some extent. To provide a meaningful metric, we consider thresholds that focus on exposure to severe events and high levels of vulnerability. We identify people at high risk from climate-related hazards as those who are both exposed and likely to suffer severe consequences (i.e., who are highly vulnerable). Figure 1 summarizes our approach. The exposed population is estimated using gridded spatial data derived from remote sensing and hazard modeling, whereas vulnerability is largely measured from household surveys (see Methods). The result is an estimate of the number of people likely to experience substantial welfare losses due to climate hazards in their lifetime.
Global exposure to extreme weather events
We examine exposure to four types of climate-related hazards: agricultural droughts, floods, heatwaves, and tropical cyclones. The exposed population is defined as those living in areas where events of a given return period, or frequency, exceed a critical intensity threshold (Table 1). As a benchmark, we consider 100-year return period events, which correspond with a 1% annual probability of occurrence, or 52% probability over the average life expectancy of 72 years. People are more likely than not to experience these events in their lifetime. Each type of hazard has distinct impacts, affecting lives, productivity, or assets in different ways. This makes it difficult to select equally severe exposure thresholds across different contexts. We identify critical thresholds for each type of hazard from existing literature.
Locations exposed to severe drought are based on FAO’s Agricultural Stress Index (ASI) and restricted to rural areas13. Agricultural production losses are expected when the vegetation health index falls below 35% over a growing season and this threshold is used by the ASI to define areas affected by severe drought14. Considering the challenges in modeling the probability of drought events, we define exposed locations as those where more than 30% of the land area experienced severe drought (ASI > 30) for any season over the last 39 years with observations15. We consider pluvial, fluvial and coastal flooding using modelled probabilistic inundation maps from Fathom and Deltares16,17. Locations are considered exposed to severe flooding if the maximum inundation depth exceeds 0.5 m from any type of flooding. Floods of this depth are associated with disruptions to livelihoods and economic activities18. Estimates of the share of residential assets lost from a 0.5 m fluvial flood range between 22-49% across regions19. Exposure to severe tropical storms is based on the modelled STORM wind speed data for different return periods20,21. We use a wind speed threshold corresponding with a Category 2 tropical cyclone on the Saffir-Simpson scale to identify exposed locations. Cyclones of this intensity are associated with damages to buildings and infrastructure22,23. For heatwaves, we use a 5-day average maximum Wet-Bulb Globe Temperature (WBGT) of 33°C as the threshold. This corresponds with the reference upper limit for healthy, acclimatized humans at rest to keep a normal core temperature24. At this temperature, heat-related mortality and hospital visits increase, and physical work capacity is reduced to around 50%25,26. WBGT is approximated using the Environmental Stress Index (ESI), derived from hourly ERA5 reanalysis27,28.
Table 1: Hazard exposure thresholds
Hazard
|
Return period
|
Intensity threshold defining an exposed location
|
Agricultural drought
|
Historical (39 years)
|
> 30% cropland or pasture affected and rural
|
Flood
|
100 years
|
> 0.5 m inundation depth
|
Heatwave
|
100 years
|
> 33°C 5-day maximum Wet-Bulb Globe Temperature
|
Tropical cyclone
|
100 years
|
≥ Category 2 wind speed
|
We estimate that 4.5 billion people, or 57% of the global population, are exposed to at least one hazard exceeding intensity thresholds. Figure 2a maps the share of population exposed to any hazard. By relying on spatial data with global coverage we can determine the exposure status of every person in every country, whereas when we consider vulnerability using household surveys, coverage is limited by data availability. The share exposed is higher in South Asia (87%) and East Asia and the Pacific (69%), but local hotspots exist within every region and country (Extended Data Table 1). The global population exposed to any hazard decreases to 47% when considering more frequent events, with a 20-year return period and the same intensity thresholds (Extended Data Table 2).
Our method assigns every population grid cell (approximately 90 x 90 m) to one of 16 exposure categories representing all possible combinations of hazards. This prevents double counting and permits analysis of exposure to multiple hazard types, as shown in Figure 2b. Heatwaves are the hazard with highest share of the population exposed (40%) and dominate in regions closer to the equator (Extended Data Figure 1). Around three quarters of those exposed to cyclones (8% of the total population) and more than half of those exposed to floods (10%) are also exposed to heatwaves, influenced by tropical weather patterns, topography and urbanization in these locations. A substantial share of the population is exposed to severe droughts (18%), considering this only counts people in rural areas, of which more than a third are exposed to another type of hazard. Overall, 16% of the population are exposed to more than one above-threshold hazard but only 1.6% are exposed to more than two. Figure 2b does not visualize very small intersections such as the population exposed to all four hazards (0.04%), but there are some people exposed to all possible hazard combinations.
We also classify the population by degree of urbanization, which is necessary to merge exposure with household data on vulnerability specific to the rural and urban population. Almost three quarters of the rural population, defined by the degree of urbanization methodology29, are exposed to severe drought. However, a relatively larger share of the urban population is exposed to cyclones, floods and heatwaves (Extended Data Table 3). Exposure to flooding is highest in peri-urban and suburban areas on the outskirts of cities (12% of the population), where formal land-use planning may be less common. Results highlight varying rates of population exposure across urbanization levels and the need for tailored risk management strategies.
Vulnerability to extreme weather events
To identify vulnerable households, we use seven indicators that proxy different dimensions of vulnerability (Figure 1). These are informed by a large literature identifying the type of households with a high probability of experiencing severe losses when exposed to extreme weather events. They capture both household’s physical propensity to experience loss of income, assets or health and their inability to cope with and recover from losses. A household is considered vulnerable if they are highly vulnerable on any dimension. This approach gives an equal importance to each dimension. In reality, certain dimensions may be more critical depending on the context or type of hazard, and the interaction between dimensions may be important. Our approach does not currently incorporate this complexity; however, we demonstrate the potential for such extensions by mapping the complete joint distribution of hazard exposure and vulnerability dimensions (Extended Data Figure 4).
The specific measures of vulnerability were selected because they have well-recognized global definitions and are widely available in survey data. The indicators are mostly derived from household surveys that are representative of the population at subnational rural-urban level, allowing global scale analysis of the population at risk with unprecedented granularity. Most indicators are derived from harmonized household survey microdata available from the World Bank’s Global Monitoring Database (GMD), while others are fused into the GMD household surveys using data from other sources including the Findex individual-level microdata for access to finance and ASPIRE for social protection (see Methods and the replication package for details)30,31.
Physical propensity to experience severe loss is proxied using three indicators. Households are considered highly vulnerable if they lack access to improved drinking water. Improved sources of water can protect people from contamination when storms and floods occur or lessen the impacts of droughts and heatwaves32. Households are also considered highly vulnerable if they lack access to electricity. During heatwaves, households with electricity are much more likely to have assets such as fans and fridges that can alleviate impacts. Lastly, access to services and markets enhances resilience by providing access to healthcare and other support, and ensuring households can access alternate employment opportunities and markets for goods (including food when local production fails)33. Households are considered highly vulnerable if they are rural and located more than 2 km from an all-season road, consistent with the Rural Access Index (SDG 9.1.1).
Inability to cope with losses is proxied using four indicators. First, households are considered highly vulnerable if they live below the international poverty line of $2.15 (2017 PPP) per person per day. Should a hazard occur, they would be unable to meet basic needs Second, households are considered highly vulnerable if no adult member has completed primary education. Educational attainment captures both the ability to understand and respond to information such as early warnings, as well as the ability to switch livelihoods when faced with climate-related hazards34,35,36,37. Third, households are considered highly vulnerable if they do not have access to a bank or mobile money account. Borrowing money or accessing transfers from family members is a widespread and effective coping strategy in the aftermath of a disaster38,39,40. Access to a bank or mobile money account increases the geographical reach of these transfers so that they can be used to manage climate shocks. Fourth, there is considerable evidence that public cash transfers and other social protection systems help households manage shocks41,42,43,44,45,46,47. Ideally, to measure this dimension we would use data on whether a household can be covered by social protection should a crisis occur. The number of beneficiaries at one point in time may be a poor proxy for this potential coverage, especially with the development of adaptive social protection systems that can scale up in times of crisis. To better account for the effect of social protection systems, we assume that individuals contributing to or receiving social insurance and those currently receiving social protection transfers are not highly vulnerable48,49,50.
The share of the population highly vulnerable on each dimension in 2021 ranges from 2% (access to services and markets) to 19% (access to social protection), based on data for 160 countries accounting for 94% of the global population (Extended Data Table 4). 14% of people lack access to finance and 6-10% are considered highly vulnerable on the remaining dimensions. The share of population vulnerable on any dimension is 36% in our sample. Figure 3a maps the stark differences in vulnerability across the globe. Sub-Saharan Africa has 90% of its population highly vulnerable on at least one dimension, whereas less than 3% are highly vulnerable in high income countries. The dimension on which the largest share of the population is vulnerable varies substantially across countries (Extended Data Figure 2).
While one could expect income to be a good proxy for other dimensions of vulnerability, the correlation across dimensions is not particularly high (Extended Data Figure 3). This is underscored by the fact that although two-fifths of those highly vulnerable are vulnerable on multiple dimensions (16% of the global population), three fifths are vulnerable on one dimension (Figure 3b). This emphasizes the different nature of vulnerability across households, and the complexity of resilience-enhancing policies, which require different interventions in different places, even within countries. Lack of access to social protection and lack of financial inclusion are the dimensions on which people that are not vulnerable on other dimensions are most likely to be vulnerable (Figure 3c).
The global population at high-risk
We estimate the population at risk from climate-related hazards by merging the population exposure estimates derived from high resolution spatial data with information on household vulnerability from surveys. People at high risk are defined as those exposed to any hazard and vulnerable on any dimension, based on specific thresholds (Figure 1). We find that almost 1 in 5 people (19%) are at high risk from climate-related hazards based on data from 160 countries for 2021 (Extended Data Table 5).
Figure 4a maps the share of population at high risk in 2021, highlighting spatial inequalities arising from the intersection of exposure and vulnerability. Nearly everyone who is exposed in Sub-Saharan Africa is considered highly vulnerable and therefore at high risk. Sub-Saharan Africa had the highest vulnerability rates for 2021 (8-71%) on each dimension except access to finance (30%), which is also high in the Middle East and North Africa (39%). In contrast, Asia has higher rates of population exposure on average, but lower vulnerability. Population exposure is similar in North America and Latin America and the Caribbean at the region level, but there is a considerable difference in the share at high risk because very few are counted as highly vulnerable in North America when using our measure, which is extreme by high-income country standards. There are 37 countries, many of them small islands, where the entire population is exposed to cyclones or heatwaves exceeding intensity thresholds, but among these the population at high-risk ranges from less than 1% to over 90% (Haiti) due to differences in vulnerability. The map also highlights significant variation within countries with subnational data.
8% of the population are exposed and vulnerable on more than one dimension. People in sub-Saharan Africa and those exposed to drought are particularly likely to be highly vulnerable on multiple dimensions. Of those exposed to drought, three fifths are highly vulnerable on multiple dimensions, while this is closer to one third for people exposed to other hazards (Figure 4b). These exposed populations facing multiple deprivations are more likely to require multiple interventions to become more resilient. We further decompose results to quantify the population exposed to each combination of hazards and facing each combination of vulnerabilities (Extended Data Figure 4). This detail is useful for informing context sensitive and multifaceted climate change adaptation strategies.
Historical trends
We estimate recent trends in those at-risk by examining how the number of people exposed and vulnerable have changed between 2010 and 2021. Given the short time trend we assume constant climate conditions between 2010 and 2021. Two dimensions of vulnerability (access to social protection and access to services and markets) are also assumed constant across time, due to lack of available time trend data. Access to social protection, services and markets has improved over the past decade, and additional work is ongoing to improve upon the time trend estimation.
With these simplifications, the share of the global population at risk to extreme weather events has decreased substantially from over 1 in 3 people in 2010 (2.5 billion) to 1 in 5 in 2021(1.5 billion) (Figure 5a). The trend can be attributed almost entirely to a decrease in severe levels of vulnerability among households in exposed locations. The share of people living in exposed locations did not change significantly at the global level as a result of net-migration and differences in population growth between exposed and unexposed places, however the absolute number of people exposed increased by 461 million. Trends in exposure for specific locations and hazards vary, for instance cities are growing faster in flood zones than in safe areas51.
Globally, the largest decrease in vulnerability was on the access to finance dimension. The share of the exposed population without a bank or mobile money account decreased from 21% in 2010 to 8% in 2021, highlighting rapid improvements in financial inclusion over the last decade (Extended Data Table 5). The share of exposed people vulnerable on income, education and access to infrastructure dimensions have each decreased by around half. The decrease in the population at high-risk over the last decade has been driven by development in some highly populated and exposed regions, with seemingly limited progress occurring in others. South Asia and East Asia & Pacific regions saw the largest decreases in their populations at high-risk, dropping from 66 to 32 percent and 32 to 11 percent respectively, due to significant improvements across most vulnerability dimensions (Figure 5b).
[1] https://scorecard.worldbank.org