A warming climate could leave some cities with less rain overall but worse floods, according to a new study from the Hebrew University of Jerusalem. The researchers found that about a quarter of the world’s urban land is on track to get drier on average while its heaviest downpours grow more intense.
The study, published in the Journal of Hydrology, was led by PhD student Raz Nussbaum with co-author Moshe Armon, under the supervision of Efrat Morin.
A quarter of the world’s cities
The team first looked at projections from 32 global climate models under a high-emissions scenario. By the end of the century, 26 per cent of the world’s urban areas are projected to see total precipitation decline while extreme rainfall intensifies. Those areas are home to about 1.5 billion people today.
The affected regions include the Mediterranean, western and southern Africa, southeastern Australia and parts of the Americas.
What that combination means for flooding in cities had received little study, the researchers said, so they set out to model it.
Weak floods weaken, strong floods strengthen
For the detailed work, the team chose the Nahal Ra’anana catchment in central Israel. They ran more than 5,300 simulations of heavy rainfall events, combining climate projections with rainfall and urban drainage models under a range of climate and development scenarios.
Future storms over the eastern Mediterranean became more compact in both space and time. In the study area, the maximum rainfall intensity over 10 minutes rose by about 20 per cent in the future-climate simulations, even as total rainfall and longer-duration rain declined.
The result was a split response. Small runoff events got smaller, but the largest ones, the kind most likely to cause flooding, got larger.
“Climate change is not simply making cities wetter or drier. It is fundamentally changing how rain falls,” Nussbaum said. In regions getting less rain in shorter, sharper bursts, “the most extreme floods could become even more extreme.”
Pavement makes it worse
The researchers also varied the share of roads, buildings and other paved surfaces in their simulations. Denser development amplified extreme runoff further, especially at the neighbourhood scale.
Paved surfaces and rooftops stop water from soaking into the ground, sending it quickly into drains. When a lot of rain falls in a short time, drainage systems may not keep up.
Nussbaum said urban flood protection will need to be rethought, not only because of climate change but because population growth and densification keep adding impervious surfaces while putting more people in harm’s way.
Planning on old rainfall records
Flood protection is usually designed around historical rainfall patterns. The researchers warn that approach may underestimate the risk from future extreme storms. They point to drainage designed for short, intense rain, along with green space, water-retention systems and climate-resilient planning.
The detailed runoff results come from a single catchment and need to be tested in other cities, the authors note. But the global analysis suggests similar rainfall trends could reach many urban areas.
The takeaway for policymakers, the researchers said, is that preparing for a drier future does not mean preparing for milder floods. Some cities may have to manage both shrinking water supplies and more destructive downpours.
Source: Nussbaum, R., Armon, M., & Morin, E. (2026). “Dual urban runoff response to urbanization and contradictory precipitation trends driven by climate change.” Journal of Hydrology, 680, 136438. doi:10.1016/j.jhydrol.2026.136438. Press release via Hebrew University of Jerusalem.
