The number is almost too large to hold: 1.81 billion people — 23% of the global population — are directly exposed to 1-in-100-year floods, defined as inundation of more than 15 centimetres across at least part of their home environment. That figure comes from a landmark 2022 study in Nature Communications by Rentschler, Salhab, and Jafino of the World Bank, covering 188 countries. [¹] This is not a forecast. It is a present-day exposure count.

GlobMaps is developing sub-national flood risk intelligence for Southeast Asia. We don't yet have a live product — but we are deep inside the data. This piece reflects what the global research tells us, and why we think province-level granularity is the critical gap.

The weight falls on Asia

The global headline conceals a critical geographic concentration. The Rentschler et al. (2022) analysis — drilling into regional breakdowns across its figures and extended data — confirms that South and Southeast Asia together account for the world's largest single regional concentration of flood-exposed people. Countries including India, Bangladesh, Pakistan, Indonesia, and Vietnam account for a disproportionate share of that 1.81 billion. [¹]

The reasons are structural: monsoon seasonality, high-density river deltas, rapid urban expansion into low-lying areas, and government data systems that often cannot resolve risk below the province level. A national flood-exposure number for Vietnam or Thailand tells a planner almost nothing about whether a specific district needs reinforced drainage or an early-warning antenna.

Deltas: where flood risk compounds

Perhaps nowhere is this more acute than in the world's river deltas. A 2015 study in Science by Tessler and colleagues documented that more than 500 million people live in and around the world's 48 major low-lying deltas — roughly 7% of the global population on just 1% of Earth's land area. [²]

These communities face a triple threat: river flooding from upstream discharge, coastal inundation from sea-level rise, and land subsidence from groundwater extraction and sediment deficit. Southeast Asia's great deltas — the Mekong, the Chao Phraya, the Irrawaddy, the Red River — are among the most densely populated and most exposed.

The policy implication is direct: these populations need risk intelligence that accounts for how these three forces interact at the local level, not just national-scale hazard maps.

The economic logic of preparedness

Flood risk is not just a humanitarian concern; it is a structural economic liability. Swiss Re's sigma series places global insured flood losses at roughly $15 billion per year averaged over 2020–2024, and the gap between insured and total economic losses is stark — insurance penetration in high-risk Southeast Asian markets remains low, meaning most losses are absorbed uninsured. Munich Re's NatCat database places cumulative insured flood losses since 1980 at approximately $260 billion globally, ranking floods second only to storms in catastrophe loss. [³]

The asymmetry between prevention and response is just as striking. A 2019 report by the National Institute of Building Sciences found that federally mandated hazard mitigation in the United States returns roughly $6 in avoided losses for every $1 invested. [⁴] For the developing-country context most relevant to Southeast Asia, the Global Commission on Adaptation (2019) cites a similar $4–$7 return per dollar invested in climate resilience. [⁵]

The data makes a consistent argument: investing in granular risk intelligence before a flood is a fraction of the cost of responding after one.

What province-level data actually changes

The gap in Southeast Asian flood risk management is not a lack of awareness of the problem — it is a lack of actionable granularity. National-level exposure statistics, however accurate, cannot tell a municipal engineer in the Mekong Delta which wards will be inundated first in a Category 3 event, or guide a development bank evaluating a climate-resilient infrastructure loan in Nakhon Ratchasima.

This is the problem GlobMaps is working to address. We are building sub-national flood risk intelligence for Southeast Asia — starting at the province level, working toward district and commune resolution — calibrated to monsoon seasonality, river discharge dynamics, and delta subsidence patterns specific to this region.

We do not yet have a finished product. What we do have is a clear view of where the data gap sits, and why it matters at the scale the research describes.

The uncomfortable truth about flood maps

Most flood maps in Southeast Asia were built for national planning, not local decision-making. They assume a static landscape when delta morphology changes year to year. They aggregate risk across administrative units that span from mountain headwaters to tidal flats.

The 1.81 billion number from Rentschler et al. is global. But the flood that displaces a family in the Mekong Delta next monsoon season will not be global — it will happen at a GPS coordinate, in a specific dry week turned suddenly wet, in a place where the levee is three years past its last inspection.

The research establishes the scale of the problem. The work is to bring it to the right resolution.

More on how we build climate intelligence for Southeast Asia at globmaps.com.

[¹] Rentschler, J., Salhab, M., & Jafino, B.A. (2022). Flood exposure and poverty in 188 countries. Nature Communications, 13, 3527. doi:10.1038/s41467-022-30727-4 — [²] Tessler, Z.D. et al. (2015). Profiling risk and sustainability in coastal deltas of the world. Science, 349(6248): 638–643. doi:10.1126/science.aab3574 — [³] Swiss Re Institute sigma (annual NatCat series); Munich Re NatCat Service. — [⁴] National Institute of Building Sciences. Natural Hazard Mitigation Saves: 2019 Report. Washington, DC: NIBS, 2019. — [⁵] Global Commission on Adaptation (2019). Adapt Now: A Global Call for Leadership on Climate Resilience.