DHI delivers a future-ready flood protection strategy combining climate adaptation, cloudburst management and sustainable urban development

 

In Karlshamn’s Vägga area, water is both an asset and a growing risk. Its coastal setting, shaped by low-lying terrain, wetlands and natural watercourses, creates a close connection between land and sea. But it also makes the area highly exposed to rising sea levels and increasingly intense cloudburst events. As climate pressures accelerate, the need for clear, actionable flood protection strategies has become critical.

DHI worked with Karlshamn Municipality to transform complex risks into confident decision-making. Using MIKE+, DHI delivered high-resolution cloudburst mapping. By combining the flood risks from rising sea levels and cloudburst events, the team defined climate-adjusted protection levels for medium- and long-term futures. The result is a fully integrated flood protection plan that combines science, planning and economics into one coherent strategy. 

 

The proposed measures deliver estimated socio-economic benefits of EUR 1–10 million — equipping the municipality with a robust, decision-ready roadmap for a safer, more resilient Vägga.

 

Challenge

Vägga presents a complex flood risk landscape where coastal flooding and extreme rainfall interact. Previous national and regional assessments have highlighted Karlshamn and Vägga as an area requiring careful consideration of flood risk. Increasing risks from sea-level rise and cloudbursts, combined with regulatory requirements under Sweden’s Planning and Building Act, created an urgent need for a clear and consistent framework to support planning and development.

 

Karlshamn Municipality needed more than analysis — they required a forward-looking decision support system to define protection levels over time and identify measures that are technically feasible, economically justified and aligned with the area’s long-term development ambitions. Of high importance was to protect the environmental and social factors, ensuring that the measures integrate well with the landscape and support the future growth of both Karlshamn and tourism.

 

Solution

DHI worked closely with Karlshamn Municipality to deliver a structured and evidence-based flood management strategy built on advanced hydrodynamic modelling and deep domain expertise. 

 

Future protection levels were established through analysing probability of extreme events over different time-horizons, combined with national guidance and supported  by advanced modelling in MIKE+. Based on the insights, climate-adapted protection levels were defined for both medium (2050–2100) and long-term (2100–2150) time horizons — providing clear, actionable design criteria for planners and decision-makers. These levels incorporated return periods, the combined effects of sea-level rise and cloudburst events and uncertainties over time to guide planning and climate adaptation measures.

 

A wide range of adaptation measures was identified, including coastal defences, quay reinforcements, nature-based solutions and strategic elevation of infrastructure. Each option was rigorously assessed through socio-economic analysis, benchmarking benefits of the protected area against a no-action scenario and evaluating impacts on economy, communities, infrastructure, environment and cultural heritage. Sensitivity analyses ensured robustness, while technical feasibility and landscape integration were assessed.

 

A key strength of DHI’s solution was its integrated methodology, which linked hydrodynamic evidence to protection levels, feasible solutions and economic justification. DHI translated complex flood dynamics into tangible, prioritised actions for specific time horizons. The result is a strategy that not only reduces risk but actively supports sustainable urban development.