This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: New research brings together recent advances in urban hydrology, boundary-layer meteorology, extreme precipitation and flood-risk research and proposes a new framework for understanding how cities and extreme rainfall interact and co-evolve. The study was led by Long Yang, a professor at Nanjing University in China.
Hayley Fowler, FRS, a professor at Newcastle University, is among the coauthors of the paper, which was published in Nature Cities. Authors from around the world contributed to the study, including experts from Princeton University, Delft University of Technology, the French National Centre for Meteorological Research and the University of Texas at Austin. At the center of the review is the concept of the urban rainfall effect—the idea that cities are not only exposed to storms but may also influence the development, intensity, movement and spatial distribution of rainfall.
The authors argue that research on urban extreme rainfall should move beyond the traditional one-way view of "rainfall drives runoff" and instead adopt a coupled framework linking urban form, rainfall processes, runoff responses and adaptation measures. The review paper identifies three major pathways through which urbanization can affect rainfall. First, urban roads, rooftops and building materials alter surface albedo, heat storage and evapotranspiration, enhancing sensible heat flux and contributing to the formation of urban heat islands.
Stronger urban heating can increase boundary-layer buoyancy, promote convective initiation and intensify short-duration rainfall under favorable atmospheric conditions. Second, dense building clusters increase surface roughness and modify near-surface wind fields and turbulent transport. Urban roughness can induce low-level convergence, mechanical lifting and enhanced rainfall downwind of cities.
Third, urban emissions provide aerosols that can act as cloud condensation nuclei or ice nuclei, altering cloud microphysical processes. Depending on moisture and stability conditions, aerosols may either suppress warm-rain formation or delay precipitation onset while allowing storms to grow deeper and more intense. Together, these processes mean that the urban rainfall effect is not simply a matter of cities increasing or decreasing rainfall.
Instead, the response depends on city size, urban morphology, building density, background circulation, moisture availability, aerosol loading and storm type. Fowler, FRS, professor of climate change impacts at Newcastle University's School of Engineering and a director of the Centre for Climate and Environmental Resilience, said, "We know that climate change is intensifying the short-duration rainfall extremes that can overwhelm urban drainage and cause devastating flash floods. "This review adds an important piece to that picture: cities are not simply passive recipients of extreme rainfall but can themselves influence the processes that shape storms.
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