Rising Flood Risk: Is Development Heading Into Dangerous Waters?

By Mia Taylor October 4, 2023

Global urbanization is steering habitats into high-risk flood zones, amplifying the hazard as climate change escalates.

As the world embraces the phenomenon of rapid urbanization, the mounting construction in flood-prone areas is raising alarms, finds new research. This elevates disaster vulnerability in the face of a burgeoning climate crisis. Between 1985 and 2015, the study reveals, settlements ranging from small rural hamlets to sprawling mega-cities with maximum flood hazard exposure saw a 122% growth.

Paolo Avner, a senior economist at the World Bank and a key contributor to the study, expressed concerns saying, “In a period when human habitats should be adapting to climate change, numerous countries are, in fact, rapidly heightening their susceptibility to floods. This is a worrying trend, particularly as climate change is amplifying flood disasters globally.”

To comprehend the populations at the greatest flood risk, researchers explored global flood hazard datasets and annual settlement footprint data spanning the three decades from 1985 to 2015. Discoveries from this research period showed urbanization outpacing 85% global settlement growth, specifically in high-hazard flood zones, over lower-risk areas.

In 2015, globally, over 11% of developed areas encountered high or exceptionally high flood risk, defining areas susceptible to flood depths reaching at least 50 cm (17in) during once-in-a-century flooding events.

Of all flooding types, coastal flood vulnerability exhibited the quickest growth. The analysis concluded that notwithstanding all global regions and income groups facing noteworthy flood risks, some endure more danger than others.

East Asia and the Pacific region exhibited maximum flood exposure, while North America and sub-Saharan Africa showed the least, as per the report's findings. Upper-middle-income countries had the most significant share of new human settlements in the highest flood risk zones. With the acceleration of its urbanization, China houses nearly half of all new settlements constructed in high flood hazard areas between 1985 and 2015.

Though wealthier countries experienced a relative slowing of growth in flood-prone zones over the same 30-year period, many (including the US, Japan, and the Netherlands) had numerous settlements in high flood risk areas pre-1985 and have had to invest considerable funds for their protection.

Land scarcity is a primary reason behind the meteoric rise in constructions on flood-vulnerable sites. The safer flood areas are mostly already developed; hence new constructions disproportionately occur in floodplains and other previously shunned regions. Various reasons fuel this trend—above all, economic opportunities that outweigh the looming disaster risk, like major port cities or beachfront communities. Meanwhile, dire circumstances like inadequate flood data, poor urban planning, and lax regulation contribute as well.

An example is Southwest Florida, experiencing explosive population growth due to its sunny weather and affordability, despite the rising risk of severe hurricanes. This growth surge coincided with the state relaxing laws around high-risk and low-lying area construction.

To mitigate this increasing threat, the report urges policymakers and planners to invest in initiatives such as disaster preparedness, early warning systems, and evacuation blueprints in high flood risk regions, and to reassess land use plans and building codes in growing risk areas.

Though not involved in the study, Robert Nicholls, Professor of Climate Adaptation at the University of East Anglia, validated the report's methodology, terming its findings as "not surprising, but new." He added that, as evidenced by the study, enhancing risk sans climate change is worrying; climate change will substantially escalate these risks in the future.