Heavy Rain Risk Management for Municipalities

In short. Heavy rain risk management is the structured path from hazard to measure. You link the heavy rain hazard map (where does how much water stand?) with the vulnerability of assets (what is affected there?) and derive prioritised measures from this. The recognised approach is described in DWA code of practice M 119. It is not a one-off report but an ongoing process of analysis, implementation and review.

Why this matters for your municipality. Without systematic prioritisation, you spend money where pressure currently arises, not where the greatest damage is threatened. Heavy rain risk management makes visible which assets (daycare centre, care home, substation) are at risk from which event, and which measure reduces the most risk per euro. This is the basis for robust council resolutions and funding applications.

What does heavy rain risk management include?

DWA code of practice M 119 distinguishes three components. First, hazard assessment: a hydraulic simulation showing how water flows off at the surface under defined scenarios, the result is the heavy rain hazard map. Second, risk analysis: you overlay the hazard map with actual land use and assess which assets are affected and how severely. Third, the action concept: municipal, private and behavioural measures, prioritised by effectiveness and effort. Only this third step turns data into action.

How do you prioritise measures sensibly?

Prioritisation means weighing damage potential against feasibility. An emergency water route that relieves an underpass can be cheaper and more effective than isolated property protection at many individual buildings. Criteria include the number and sensitivity of affected assets, the probability of occurrence, the costs, and whether a measure can be combined with construction work that is already planned. Anyone renovating streets can often plan in retention with little additional effort.

Who needs to be involved for it to work?

Heavy rain risk management is not the task of a single department. Civil engineering and municipal drainage bring the hydraulics, urban planning brings land use, the environmental department brings nature-based approaches, the fire service and regulatory office bring hazard response. Equally important: private property owners. A large part of property protection, backflow flaps, adapted basement access, barriers, lies in private hands. Without information and participation, the concept stalls halfway.

The honest limit. Risk management assesses and prioritises, it builds nothing. Between the adopted concept and the completed measure lie planning, procurement, financing and often several budget years. And the models work with assumptions: soil permeability, blockage of culverts or sewer filling can never be represented exactly. The map shows scenarios, not a forecast of the next event.

When KomAdapt is worthwhile. If hazard, asset exposure and measures are kept in separate files at your organisation, prioritisation becomes a laborious task that has to be redone from scratch with every update. KomAdapt brings the risk, prioritisation and reporting steps together in one model, so you can derive the impact logic for resolutions and funding applications directly.

_What is the difference between a hazard map and risk management?_ The hazard map shows where water stands and flows during a specific rain event, the pure physical hazard. Risk management assesses what is affected, how severe the damage would be, and which measures reduce it. _Which set of rules applies?_ Central is DWA code of practice M 119. DWA standard sheet A 118 and state guidance documents provide additional requirements. These standards are the reference against which funding applications and expert reports are measured. _What does building it up cost?_ The hydraulic hazard map, the most expensive item, is often in the mid five-figure range for smaller municipalities, and higher for large cities. Part of this is fundable through the federal DAS funding guideline and state programmes; however, there is currently no open DAS application window (last reviewed: August 2026). _How often does risk management need to be updated?_ It is an ongoing process. Triggers for revision include new development, implemented measures, improved data, or an event that has occurred. As a guide: every five to ten years. _Can small municipalities also build heavy rain risk management?_ Yes, in a scaled-down form. Inter-municipal cooperation reduces costs. A realistic scope that matches staff capacity is important.

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