Stockholm areas at risk of flooding from extreme rainfall

Stockholm County is grappling with a heightened threat of flooding, particularly from "hundred-year" rain events, as climate change intensifies rainfall.

The Länsstyrelsen (County Administrative Board) has released detailed hot- and risk maps for 21 municipalities, pinpointing three waterways as critically vulnerable: Bällstaån, Oxundaån, and Tyresån.

Johanna Sörensen, a researcher in technical water resource management at Lund University, explains that a warmer climate allows the atmosphere to hold more moisture, leading to more intense downpours. "When the climate gets warmer, the air can hold more moisture. The more moisture the air can hold, the more intense the rain becomes," she stated.

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When the climate gets warmer, the air can hold more moisture. The more moisture the air can hold, the more intense the rain becomes.

The mapping categorizes areas by "threat," indicating where water might reach, and "risk," detailing potential damage to people, properties, homes, and natural environments. Urban areas, with their extensive impermeable surfaces like asphalt and concrete, are especially susceptible. "Rain events cause the greatest impact in cities. There are many hard surfaces like asphalt, concrete, and a lack of green spaces, which causes water to run off very quickly. The sewage system cannot handle the volume of water," Sörensen noted.

Bällstaån, flowing through Järfälla and Sundbyberg, poses a significant risk, potentially affecting areas like Bromma and Spånga, and endangering schools, preschools, and hospitals. Oxundaån's overflow could impact Rotebro and Upplands Väsby, threatening residential areas and cultural heritage sites. Tyresån's flooding could affect Trångsund and Tyresö, impacting schools, cultural landmarks, and nature reserves.

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Rain events cause the greatest impact in cities. There are many hard surfaces like asphalt, concrete, and a lack of green spaces, which causes water to run off very quickly. The sewage system cannot handle the volume of water.