Floods in cities are primarily triggered by extreme rainfall events. Global warming is expected to increase the frequency and magnitude of extreme weather events, including extreme rainfall. However, global warming is not the only factor affecting extreme rainfall; the built environment also has a significant impact on rainfall intensification. Therefore, it is crucial to understand how urbanization combined with climate change will affect rainfall patterns in the future.
By using climate models, different scenarios of climate change and urbanization can be considered to explore changes in rainfall dynamics. Models of hydrodynamics can be used to assess changes in flood regimes at the city scale.
By using this model framework, mitigation steps can be taken to reduce future flood risks and damages. The steps that can be taken include revising and planning urban drainage systems in a better way or developing designated storage spaces for excess water (e.g., flooding natural parks or empty parking lots).
Improved early warning systems are also essential to warn people living in cities in case of flooding. Based on the understanding of how cities affect rainfall dynamics, better nowcasting models (i.e., short-term forecasts for rain and flooding) can be developed. In addition to the development of nowcasting tools, the challenge is informing the public about approaching floods in real-time.
New approaches for delivering warnings and their implications to the public should be considered, such as setting up unique digital platforms in flood-prone cities.
Lastly, some cities will likely be more exposed to a risk of compound flood events in the future, for example, the simultaneous occurrence of pluvial (of direct rainfall) and fluvial (of high river levels) floods. Due to their rarity, these compound events may not yet be known in historical records, which means that emergency services lack the planning and practice to deal with them. Nevertheless, simulation of compound events can support emergency planning, reducing the risk of being surprised by an unexpected severe flood in the future.
“It is crucial to understand how urbanization combined with climate change will affect rainfall patterns in the future.”
Prof. Nadav Peleg is a hydrometeorologist at the Institute of Earth Surface Dynamics where he directs the group of Hydrometeorology and Surface Processes. He was appointed as an Eccellenza Assistant Professor at UNIL in August 2021, leading the SNSF project “Rainfall and Floods in Future Cities”.
This article is related to the presentation “How climate change and urbanization will affect floods in future cities?” that he did in our CLIMACT Seminar Series. Watch Episode 4.