The World’s Costliest Floods

Floods are sometimes called the “quiet catastrophes” of the climate system. They unfold in slow motion compared with earthquakes or tsunamis, but the bill they leave behind is anything but quiet.

Across the world, river and flash floods are among the most economically destructive natural hazards. Global disaster data show that floods, along with tropical cyclones, account for a large share of natural-disaster losses every year. In 2024 alone, natural hazards caused about US$242 billion in economic damage worldwide, and a significant slice of this came from flood events.

Reinsurer statistics tell the same story. Munich Re estimates that so-called “secondary perils” such as floods, severe storms, and wildfires have tripled their global losses since the early 2000s, now averaging around US$160 billion a year in inflation-adjusted terms. And in 2024, total catastrophe losses reached roughly US$320 billion, with insured losses around US$140 billion, one of the highest years on record.

This article zooms in on the costliest flood disasters in modern history, measured by economic loss, and what they reveal about how climate, development, and risk management intersect. It uses a combination of reinsurance data, academic studies, and global disaster databases, anchored around a detailed ranking by Aon, a major global risk and insurance broker.

How We Measure “Costliest” Floods

Before ranking the world’s most expensive floods, it’s important to clarify what we mean by “costliest.”

Economic loss vs. human loss

Some of history’s deadliest floods, like the 1931 Yangtze–Huai River floods in China, killed hundreds of thousands to millions of people but occurred in relatively poor, rural economies with fewer high-value assets. Estimates for the 1931 disaster’s death toll range from about 422,000 to several million, making it one of the deadliest natural disasters in recorded history.

Yet in dollar terms, its economic losses are smaller than today’s disasters because:

• The value of exposed infrastructure and housing was lower.

• Modern accounting of indirect losses (supply chains, business interruption) did not exist.

• Inflation has massively changed the value of money over nearly a century.

Here we focus on economic loss:

• Direct losses – physical damage to homes, factories, roads, rail, farms, and public assets.

• Indirect losses – lost output, supply-chain disruption, reduced tax revenues, emergency measures, and productivity impacts.

Different datasets define and estimate these categories slightly differently, which is why you often see ranges rather than single, precise numbers.

Data sources and methodology

To keep things consistent, this article primarily relies on Aon’s 2025 Climate and Catastrophe Insight report, which includes a global ranking of the Top 10 Costliest Floods by Economic Loss (1900–2024) in both nominal and inflation-adjusted 2024 US dollars.

We cross-check these figures with:

• EM-DAT, the international disaster database run by CRED, which records human and economic losses globally.

• Munich Re’s NatCatSERVICE and thematic reports on floods and weather disasters.

• World Bank, academic, and policy studies on specific events (e.g., Thailand 2011, Yangtze floods, Mississippi floods).

Because different institutions use different methodologies, not every figure will match exactly. The ranking below follows Aon’s dataset for comparability, while the narrative notes where other credible sources report different numbers.

The Top 10 Costliest Flood Disasters (1900–2024)

According to Aon, the ten costliest floods in the modern record have all caused at least US$36 billion in economic losses when converted into 2024 dollars.

Table 1 – Top 10 Costliest Floods by Economic Loss (1900–2024, Aon)

Source: Aon, Climate and Catastrophe Insight 2025, Exhibit 55.

A few patterns jump out immediately:

• Asia dominates the list – 8 of 10 events are in Asia, and 6 involve China’s large river basins.

• China appears repeatedly, reflecting its combination of huge river systems, dense population, and rapid economic growth along floodplains.

• Only one U.S. event (the 1993 Mississippi floods) and one Japanese event make the list.

• Europe appears once, but powerfully, with the unprecedented 2021 “Bernd” floods.

It’s also worth noting that other sources sometimes feature different “top” floods. For example, one widely cited list estimates that the 2020 South Asian floods (including India, Bangladesh, Nepal and others) caused about US$105 billion in economic loss. If that figure holds under stricter catastrophe modelling, it would rival or exceed some events here. Aon’s ranking, however, uses its own per-event definitions and modelling, which is why it’s slightly different from other compilations.

With those caveats in mind, let’s dive into what made each of these events so costly.

1. 2011 Thailand Floods – When a Regional Flood Shook Global Supply Chains

The 2011 Thailand floods are ranked as the costliest flood disaster in modern history in inflation-adjusted terms.

What happened?

Beginning in mid-2011, a combination of:

• exceptionally heavy monsoon rainfall,

• upstream runoff from the Chao Phraya basin,

• and complex reservoir management challenges

led to massive flooding that ultimately inundated much of central Thailand, including key industrial areas north of Bangkok.

At the peak:

• 65 of 76 provinces were declared disaster zones.

• More than 20,000 square kilometers of farmland were affected.

The economic bill

The World Bank estimated damages and losses of 1.425 trillion baht, about US$45.7–46.5 billion at the time – roughly 12–13% of Thailand’s GDP. Aon’s global ranking places the event at US$45 billion nominal and US$63 billion in 2024 dollars.

Swiss Re later noted that total economic losses were around US$46 billion, about US$55 billion in “current” terms, with insured losses near US$15 billion – the highest insured river-flood loss ever recorded.

Key reasons the damage was so large:

• Industrial concentration: Roughly 900 factories in seven industrial estates were inundated, many belonging to automotive and electronics multinationals.

• Global dependence on Thai manufacturing: Thailand supplied around a quarter to nearly 40% of the world’s hard disk drives at the time, depending on the estimate. Flooded HDD and auto plants triggered global supply shortages and price spikes through 2012.

• Long duration: In some estates, factories were submerged for weeks to months, leading to prolonged business interruption.

Insurance covered only a portion of the losses. Industry analyses suggest insured losses of US$12–15 billion, meaning roughly two-thirds of the losses were uninsured and borne directly by firms, households, and the Thai state.

Lasting impacts

The 2011 floods catalyzed:

• Major upgrades in industrial estate flood defenses,

• Reforms in Thailand’s disaster management and insurance regulation,

• And a re-evaluation of concentrated supply chains by global manufacturers.

For risk analysts, the event became the textbook example of how a regional flood can create a global economic shock.

2. 1998 Yangtze River Floods – A Turning Point for China’s Flood Policy

The 1998 China floods along the Yangtze, Nen, Songhua and other rivers are remembered as both a humanitarian tragedy and a pivotal moment for China’s water management.

Scale and human impact

• Duration: June–September 1998.

• Deaths: estimates range from 3,704 to around 4,150.

• People affected: well over 180 million.

Economic losses

Contemporary estimates put direct economic damage in the range of US$20–25 billion at late-1990s prices. Later analyses that account for wider impacts and inflation put total losses much higher – on the order of US$70 billion in 2015 dollars.

Aon’s ranking, using its own normalization methods, lists the event at:

• US$31 billion nominal,

• US$61 billion in 2024 dollars,

making it the second-costliest flood in the modern record.

Why it was so expensive

Several factors compound here:

• Large exposed population in the floodplains of the middle and lower Yangtze.

• Degraded floodplains and lakes – decades of land reclamation and levee building had reduced natural storage capacity.

• Extensive damage to agriculture, housing, and transport infrastructure across multiple provinces.

The 1998 disaster triggered a major policy shift:

• China launched ambitious reforestation and “grain-for-green” programs,

• Strengthened reservoir and dike systems,

• And began re-allowing some floodplains and lakes to act as natural buffers.

From a risk perspective, 1998 became the reference point for “worst-case” Yangtze floods – until increasingly intense events in 2010, 2016, and 2020 showed that the system remains under pressure.

3. 2010 Yangtze River Floods – Repeated Shock to a Growing Economy

Twelve years after 1998, southern China again experienced catastrophic flooding across the Yangtze basin in 2010.

• Deaths: around 2,000 people across multiple events and landslides.

• Impacts: tens of millions affected, extensive crop and property damage.

Aon’s ranking assigns:

• US$39 billion nominal,

• US$56 billion in 2024 dollars,

placing the 2010 Yangtze floods as the third-costliest flood event globally.

Other analyses highlight:

• Economic losses around US$31 billion (2014 USD) for the July–August 2010 floods alone.

The event revealed:

• Persistent vulnerabilities in river-basin management despite post-1998 reforms.

• Extremely low insurance penetration – one Aon Benfield analysis of another major Chinese flood season (2016) found only about 1.5–2% of economic losses were insured, a figure that is indicative for several Chinese flood seasons.

4. 2021 Western Europe Floods (“Bernd”) – Europe’s Costliest Flood Disaster

In July 2021, a slow-moving low-pressure system nicknamed “Bernd” stalled over Western Europe, dumping record-breaking rainfall over parts of Germany, Belgium and neighboring countries.

Human and economic impact

• Duration: 12–25 July 2021.

• Deaths: at least 243 people (196 in Germany, 39 in Belgium).

• Total damage: around €46 billion (US$54 billion in 2021) across Europe, with €33.4 billion in direct damage in Germany alone.

Munich Re describes the July 2021 floods in central Europe as the costliest flood-related catastrophe ever recorded globally, with aggregate inflation-adjusted losses of about US$59 billion, and more than US$15 billion in insured losses.

Aon’s ranking assigns:

• US$46 billion nominal,

• US$53 billion in 2024 dollars,

placing the event fourth on the global list of costliest floods.

Why the losses were so large

• High asset values: The floods devastated wealthy regions with dense infrastructure – small river valleys lined with homes, businesses and roads.

• Record rainfall: In parts of western Germany, rainfall totals broke 100-year records, overwhelming flood defenses and warning systems.

• Critical infrastructure damage: Bridges, rail lines, water treatment plants and entire town centers were destroyed, multiplying indirect losses.

The disaster has spurred intense debates in Europe about:

• Updating flood hazard maps for a warmer climate,

• Strengthening early-warning systems,

• And increasing insurance coverage in high-risk areas.

5. 1993 Mississippi River Floods – The Costliest River Flood in U.S. History

The Great Midwest Flood of 1993 remains the benchmark U.S. river flood from a damage perspective.

Event overview

• Duration: June–August 1993.

• Region: Upper Mississippi and Missouri River basins.

• Deaths: roughly 38–50 people.

Economic losses

Contemporary estimates of damage ranged from US$12 billion to US$20 billion (early-1990s dollars), including:

• Huge agricultural losses – millions of acres of farmland flooded, crop yields down by about 30% in some states.

• Extensive damage to housing, levees, roads, rail, and navigation infrastructure.

Aon’s normalized figures put the event at:

• US$21 billion nominal,

• US$46 billion in 2024 dollars,

making it the fifth costliest flood worldwide.

Lessons

The 1993 disaster prompted:

• A reassessment of the levee-centric approach on the Mississippi.

• Increased investments in floodplain buyouts and wetland restoration.

• Stronger cooperation across states and federal agencies on flood risk management.

6. 2020 China Seasonal Floods – A Long, Expensive Rainy Season

The 2020 China floods were driven by an unusually prolonged East Asian monsoon, with heavy rainfall across the Yangtze and other basins.

• Duration: early June to September 2020.

• Deaths: at least 219 dead or missing.

• People affected: more than 63 million.

• Direct economic losses: about 178.96 billion yuan (≈US$32 billion) by August–October 2020.

Aon’s ranking places the 2020 seasonal floods at:

• US$35 billion nominal,

• US$43 billion in 2024 dollars,

ranking sixth globally.

Again, much of this loss was uninsured, highlighting the persistent “protection gap” in China’s flood-prone interior regions.

7. 1931 Yangtze River Floods – Catastrophic Loss of Life, Rising Economic Re-estimates

The 1931 floods in central and eastern China, centered on the Yangtze and Huai rivers, are widely considered one of the deadliest natural disasters in human history.

Human toll

• Duration of main flood: summer 1931, with broader impacts into 1932.

• Death estimates:

  • Official contemporary estimates: around 140,000 drowned, with about 2 million total deaths including famine and disease.

  • Later reconstructions suggest 422,000 deaths to several million, making precise numbers impossible but confirming an enormous catastrophe.

Economic loss in today’s terms

At the time, China was much poorer, with limited industrial assets. Direct damage estimates were modest in nominal dollar terms. But when Aon normalizes historic events to 2024 dollars, the 1931 floods still amount to:

• US$2.0 billion nominal,

• US$42 billion in 2024 dollars,

placing them seventh on the global economic-loss ranking.

The 1931 catastrophe underlines a key point: even when economic losses look smaller than modern disasters, the human suffering can be vastly greater. Today’s rankings focus on money, but for policy, the dual lens of lives and livelihoods remains essential.

8. 1953 Japan Floods – The Northern Kyushu Disaster

In 1953, Japan’s northern Kyushu region was hit by devastating floods caused by torrential Meiyu-front rains.

• Event: often referred to as the 1953 Northern Kyushu flood.

• Deaths: about 771 people dead or missing.

• Damage: tens of thousands of homes flooded; economic losses estimated at ¥17.3 billion at the time, equivalent to roughly ¥120 billion in early-2000s yen.

Aon’s ranking aggregates these and related 1953 floods as “Japan Floods”, with:

• US$3.2 billion nominal,

• US$38 billion in 2024 dollars,

placing them eighth globally.

The event occurred early in Japan’s rapid development period, and together with other mid-20th-century disasters, shaped the country’s now highly sophisticated flood control and warning systems. Modern assessments note that while flood fatalities in Japan have generally declined over the decades, economic damages have risen again as heavier rainfall events become more frequent under climate change.

9. 2016 Yangtze River Floods – The Cost of “Secondary” Hazards

The 2016 China floods affected much of southern and central China, again heavily impacting the Yangtze basin.

• Duration: June–September 2016.

• Deaths: at least 449 (floods and related tornadoes).

• Economic losses: around US$22 billion by some estimates; an Aon catastrophe briefing put total combined losses at US$33 billion, with about US$28 billion in the Yangtze basin alone.

Insurance payouts were tiny in comparison: less than 2% of economic cost, highlighting how exposed but uninsured many households and farmers remain.

Aon’s long-term ranking lists the 2016 Yangtze floods as:

• US$28 billion nominal,

• US$37 billion in 2024 dollars,

ninth on the global list.

The event is often cited in the insurance industry as a classic “secondary peril” catastrophe – not a single headline-grabbing hurricane or mega-quake, but a sprawling season of floods that quietly generates tens of billions in losses.

10. 2021 China Seasonal Floods – Henan, Zhengzhou, and Beyond

In summer 2021, China again faced a severe flood season, with particularly extreme rainfall in Henan province and the city of Zhengzhou.

• A single three-day event in Zhengzhou produced rainfall totals described as “once in a thousand years” by local officials.

• Deaths: at least 398 people dead or missing in Henan; nearly 14 million affected.

• Direct economic losses in Henan alone: about 120.06 billion yuan (≈US$16.5–19 billion).

Across China, flood-related events in 2021 generated total economic flood losses around US$25 billion, according to Swiss Re, making China’s flood bill the second-highest globally that year after Europe’s.

Aon’s ranking aggregates multiple 2021 Chinese flood events as “China Seasonal Floods”, with:

• US$31 billion nominal,

• US$36 billion in 2024 dollars,

putting them tenth on the global list.

The Zhengzhou disaster also had political and social repercussions, with later research finding a surge in citizen demands for better flood protection and infrastructure resilience across China.

What Makes Floods So Economically Destructive?

Looking across these ten events, several common threads explain why flood disasters are so expensive:

1. Development on floodplains

Cities and industrial zones are often built along rivers and coasts:

• For transport and trade,

• For access to water resources,

• And because these are historically fertile areas.

Thailand’s industrial estates north of Bangkok, Germany’s Ahr valley towns, and many Chinese cities all illustrate how high-value assets cluster where water also wants to flow.

2. Hidden dependencies and supply chains

The 2011 Thai floods exposed how a local hazard can have global consequences. Hard-disk drives, car parts, and electronics all suffered worldwide shortages because:

• Production was highly concentrated in a few industrial parks.

• Other regions couldn’t easily substitute production in the short run.

Similar dynamics now concern policymakers watching Europe’s industrial corridors along the Rhine and Danube or major logistics hubs in China and the U.S.

3. Long duration and cascading impacts

Unlike a brief earthquake, major flood seasons can:

• Last for months,

• Affect entire river systems,

• And repeatedly disrupt recovery efforts.

The 1993 Mississippi flood and the 1998, 2010, 2016 and 2020 Yangtze flood seasons are classic examples where prolonged inundation amplified damage to agriculture, transport, and industry.

4. The insurance protection gap

In wealthier countries, insurance absorbs a significant share of losses – for example, around US$15 billion of the 2021 European flood losses were insured.

In many middle-income countries, however, only a tiny fraction of flood losses are insured. Studies of major Chinese flood seasons have found less than 2% of economic losses insured in some years. That means:

• Governments face large, sudden fiscal burdens.

• Households and small firms may never fully recover.

• Economic scars can last for years, especially in rural regions.

Climate Change and the Rising Cost of Floods

While no single flood is “caused” solely by climate change, there is growing evidence that warmer temperatures are amplifying flood risks:

• A global study of riverine flooding projects economic impacts rising from around US$157 billion to over US$500 billion annually by 2030, and potentially into the trillions later in the century under high-emissions scenarios.

• Europe’s average annual economic damage from extreme weather (including floods) in the early 2020s is already 2.5 times higher than in the previous decade.

• Reinsurers report that non-peak perils – floods, severe storms and wildfires – now drive much of the upward trend in catastrophe losses, even in years without mega-events like Katrina-scale hurricanes.

Recent news reinforces the pattern:

• Severe floods in southern Thailand (2025) have caused hundreds of deaths and significant agricultural and infrastructure damage, echoing (on a smaller scale) the country’s 2011 catastrophe.

• China continues to experience intense flood seasons, with government data reporting multi-billion-dollar monthly losses in some recent years.

Even when flood defenses hold, urban flash floods, overwhelmed drainage systems, and disrupted transport can impose large indirect costs.

Reducing the Economic Toll of Future Floods

The world’s costliest floods are not just historical curiosities. They are warning signals about where societies are exposed and what can be done differently.

Key strategies that emerge from post-disaster analyses include:

1. Planning with floodplains, not against them

• Restoring wetlands and flood storage areas (e.g., parts of China’s post-1998 strategy).

• Avoiding construction in the highest-risk zones or using elevated and flood-resilient designs where relocation is impossible.

2. Upgrading ageing infrastructure for a warmer climate

Many European, North American and Asian flood defenses were designed for a 20th-century climate. Events like the 2021 European floods show they need updating to handle more frequent extremes.

That means:

• Higher or more robust levees and dams where appropriate,

• But also smarter drainage systems, nature-based solutions, and early-warning technology.

3. Closing the insurance protection gap

Reducing the economic pain of floods doesn’t just mean building walls; it also means:

• Expanding affordable insurance and micro-insurance in developing and emerging markets.

• Using public–private insurance pools and sovereign risk transfer (catastrophe bonds, parametric covers) to share extreme losses.

The 2011 Thailand floods and repeated Chinese flood seasons have spurred new insurance products and regulatory reforms, but coverage remains patchy.

4. Treating supply chains as critical infrastructure

Risk management is no longer just about “our local river.” The Thai floods, European floods, and Chinese events all show that:

• Key nodes in global supply chains (industrial parks, logistics hubs) deserve the same level of flood-risk analysis as dams or ports.

• Companies need diversification, redundancy, and business continuity planning to avoid repeating 2011-style disruptions.

Conclusion – Counting the Costs, Buying Down the Risk

From Bangkok’s industrial estates to the Ahr valley in Germany and the cornfields of the U.S. Midwest, floods have quietly become some of the most expensive disasters on the planet. The ten events highlighted here alone add up to hundreds of billions of dollars in inflation-adjusted losses – and they are only a slice of the global picture.

Economic rankings can never capture the full human reality of displacement, trauma, or cultural loss. But they do highlight a stark trend:

• More people and more value are concentrated in flood-prone areas.

• Climate change is loading the dice toward heavier rainfall and more intense events.

• And the insurance and infrastructure systems we built for the 20th century are struggling to keep up.

The upside is that we have decades of lessons embedded in these disasters:

• How smart land-use policy can pull people and assets out of harm’s way.

• How investing in early warning and resilient infrastructure can pay for itself many times over.

• And how aligning financial systems – insurance, credit, public investment – with real flood risk can reduce future economic shocks.

In that sense, studying the world’s costliest floods is less about morbid record-keeping and more about buying down tomorrow’s damage bill.