Flooding

Floods have been recorded by humanity since ancient times, with stories like the Epic of Gilgamesh in Mesopotamia (~2100 BCE) and Noah’s flood (1000 - 500 BCE). These two stories are so similar in many ways that scholars now believe they record an actual flood.  The fact that flooding is the climate event most related in ancient texts speaks to the profound impact such events had on the people of the time.¹ 

Probably the best case study of this progress is the Netherlands, where the low elevation and proximity to the ocean make inundation a constant threat. Around 1000 CE, Dutch farmers began building small "dijken" to protect their farms. Following a catastrophic storm surge in 1287 that killed around 50,000 people, regional water boards began forming to build and manage dikes on a regional basis.

Dikes not only protected areas from flooding: they also allowed wetlands to be drained and reclaimed for farming. In 1953, a modern flood killed 1,836 people, breached hundreds of dikes, and flooded vast areas of farmland. This lead to a massive engineering project called the Delta Works, the largest and most sophisticated flood protection system in the world, including dams, moveable storm surge barriers, dikes, sluices, and locks. The Delta Works has been a great success: despite weather events, no fatal flooding has occurred in the Netherlands since it was built.²

The Central Valley in California was a large, sprawling wetland before it was colonized by the Spanish in the 1700s. Efforts to “reclaim” the wetlands, started by the Spanish, accelerated with the gold rush and statehood beginning in 1850. Large-scale reclamation projects were undertaken in the late 1800s and early 1900s to build levees and canals and to drain lakes. This was followed by an irrigation project involving massive dams, canals, and pumps to turn the area into reliable cropland.³

Not surprisingly, all this development and reclamation has a dark side. Colonization and development took little account of the effects on indigenous people and on the tremendous biodiversity in the area. The subsequent concentration of fertilizers in the waterways has lead to significant declines in salmon and smelt, along with many migratory bird species that use the Pacific Flyway. Overdraft (more water out than in) of the massive aquifers underlying the valley has lead to land subsidence, declining water quality, and reduced drought resilience. Efforts to remedy this situation are underway, although so far with limited success.^{5, 6}

Today, both the Netherlands and California’s Central Valley are facing threats from climate change  and aging facilities, leading to more investment in flood protection.

Rather than relying so much on “grey” infrastructure like concrete and steel facilities, a more climate-adaptive approach is being applied, allowing for spaces for rivers to overflow, creating floodplains, building parks and waterways that can absorb floodwater when needed. A 2018 report done by the Insurance Bureau of Canada (IBC)⁷ confirms the benefit of this approach quoting, “Every dollar invested in wetland conservation or restoration can yield multiple dollars in flood damage reduction.”

Here is a look at how climate change promotes flooding:

• More intense rainfall - as the atmosphere warms it holds more moisture ... about 7% more per degree Celsius. The result is more intense downfalls that create flash flooding and overwhelm drainage systems.
• Sea level rise -  melting polar ice and glaciers contribute to rising coastal sea levels. The other cause is simple thermal expansion, which accounts for almost half of the rise in sea levels.
• Snow melt and river flooding - warmer and earlier springs contribute to more fluvial (river) flooding at different times of year, and also bring changing patterns of rainfall. 
• Compound events - some of the most destructive events occur when flooding happens as a result of or in combination with large wind events. Superstorm Sandy and Hurricane Katrina are good examples.

Globally, in 2021 insured flood losses worldwide were $20 billion USD, a record high. These losses continued with catastrophic flooding in Australia, Pakistan, and Europe. In Canada, flooding is the costliest of natural perils. According to the Insurance Bureau of Canada, insured damage from flood and severe weather averaged $2 billion annually between 2009-2020 up from $400 million in prior years.⁷ In the USA, the National Flood Insurance Program (NFIP) is the primary insurance provider, covering roughly 5 million policies, but with coverage only up to $250,000 per structure. In a 2021 report, the Government Accountability Office (GOA) reported that NFIP was financially unsustainable due to climate change and outdated flood maps. Commercial flood insurance is now unavailable in some states (Florida, Louisiana, and California) due to repeated losses.^{8, 9}

Declining property values are another quantifiable impact of climate change flooding. A study done by First Street projects a reduction in real estate values due to climate related risk  of $1.47 trillion USD in the next 30 years.¹⁰ Nature reports that residential properties are overvalued by $121 - $237 billion USD due primarily to flood risk, concentrated mostly in coastal areas.¹¹

It turns out building an Ark is probably not our best long-term plan….

Reading

1. George, Andrew, trans. The Epic of Gilgamesh: The Babylonian Epic Poem and Other Texts in Akkadian and Sumerian. Revised edition. London: Penguin Classics, 2003.
2. Luyendijk, Elma. The Delta Works: The Greatest Flood Protection System in the World. Utrecht: Uitgeverij Matrijs, 2015.
3. “Central Valley Project | California-Great Basin | Bureau of Reclamation.” Accessed March 31, 2025. https://www.usbr.gov/mp/cvp/.
4. “California’s Central Valley | USGS California Water Science Center.” Accessed March 31, 2025. https://ca.water.usgs.gov/projects/central-valley/about-central-valley.html.
5. “Increased Pumping in California’s Central Valley During Drought Worsens Groundwater Quality | U.S. Geological Survey.” Accessed March 31, 2025. https://www.usgs.gov/news/state-news-release/increased-pumping-californias-central-valley-during-drought-worsens.
6. “100,000 Central Valley Residents Impacted by Contaminated Drinking Water Will Soon See Interim Solutions,” n.d.
7. Insurance Bureau of Canada. Combatting Canada’s Rising Flood Costs: Natural Infrastructure is an Underutilized Option. Toronto: Insurance Bureau of Canada, 2018. https://www.ibc.ca/on/resources/media-centre/media-releases/combatting-canadas-rising-flood-costs.
8. “Extreme Flood Events Once Again Drive High Losses in 2021, yet 75% of Flood Risks Remain Uninsured, Swiss Re Institute Reveals | Swiss Re,” March 30, 2022. https://www.swissre.com/press-release/Extreme-flood-events-once-again-drive-high-losses-in-2021-yet-75-of-flood-risks-remain-uninsured-Swiss-Re-Institute-reveals/3269ad99-b743-4398-82e3-534a87783910?utm_source=chatgpt.com.
9. U.S. Government Accountability Office. National Flood Insurance Program: FEMA Can Improve Guidance on Private Insurer Data. GAO-21-578. Washington, D.C.: Government Accountability Office, July 2021. https://www.gao.gov/assets/d21578.pdf
10. firststreet.org. “Property Prices in Peril.” Accessed March 31, 2025. https://firststreet.org/.
11. Gourevitch, Jesse D., Carolyn Kousky, Yanjun (Penny) Liao, Christoph Nolte, Adam B. Pollack, Jeremy R. Porter, and Joakim A. Weill. “Unpriced Climate Risk and the Potential Consequences of Overvaluation in US Housing Markets.” Nature Climate Change 13, no. 3 (March 2023): 250–57. https://doi.org/10.1038/s41558-023-01594-8.