Even as the climate crisis escalates and people’s vulnerability to catastrophic events increases, rapid urbanisation in flood prone areas has continued to surge according to new research.
A new study Tracking urban flood exposure: Global trends since 1985 by World Bank published in science journal Nature in October 2023 reveals that between 1985 and 2015, the number of settlements – from small villages to mega-cities – with the highest flood hazard exposure has increased by 122%. The settlement trend has continued, even as awareness of the risks of climate change has increased.
According to the study, urbanisation and economic development have traditionally gone hand in hand as cities attract people, ideas and capital and foster agglomeration economies. However, rapid urbanisation can also cause congestion effects; for instance, by increasing exposure to natural hazards and pressure on public services and infrastructure.
The effect of rapid urbanisation on flood risks and people is an intensifying challenge for low and middle-income countries. This is particularly relevant in countries that lack the capacity for risk-informed urban and infrastructure planning and the resources to invest in protection infrastructure.
As safe spaces for construction are increasingly occupied, high population density and land scarcity are driving new developments disproportionately into previously avoided areas, including riverbeds and flood plains. This is particularly true in East Asia, where high-hazard settlements have expanded 60% faster than flood-safe ones.
It is more so in middle-income countries, where economies and cities have grown rapidly over the past decades. The effects are most visible in upper-middle-income countries, which have a higher proportion of settlements in highest-hazard areas than any other group.
Such areas have grown by 184% since 1985 —nearly twice the rate of flood-safe settlements (96%). These expanding settlements in high-hazard areas lock in flood exposure, as well as future losses and the need for ever-mounting flood protection investments.
Low-income countries have seen moderate settlement growth since 1985 and this growth is occurring on safe land mostly. On average, settlements in these countries in high-hazard areas have grown 77%, compared to 87% in safe areas.
These findings have concrete implications for urban planners and policy makers. In areas where flood exposure is already high, investments in disaster preparedness and protection are crucial to mitigate losses (e.g. early warning systems, social protection and protective infrastructure).
In areas where flood exposure is still low but increasing rapidly, revision of land use and urbanisation plans are urgent priorities to avoid new construction in the highest-risk areas. Once an area is urbanised, it is impossible or expensive to reverse it, thus locking-in high-risk patterns with large economic and human consequences.
While land scarcity and geographic constraints mean that flood zones cannot always be avoided, careful planning of protection systems and disaster preparedness can support resilient development. M