RISA – Rain InfraStructureAdaptation | Umweltbundesamt

no own climate scenario developed

The Hamburg water management is facing major challenges to ensure the protection against flooding also in times of climate change. An increase in rainfall during the winter months is predicted as well as precipitation more frequently coming down as heavy rain in connection with storms and thunderstorms. At the same time the trend for sealing surfaces in Hamburg continues. In particular, heavy rainfall events can lead to an overload of the sewer and water bodies, hence flooding roads and basements.

Climate change & surface sealing

As a result of climate change, precipitation in the winter months will increase in the future. In addition, so-called heavy rain events are more likely to occur throughout the year. Heavy rain often occurs in connection with thunderstorms, which can drop significant amounts of rain in a few hours. With the ongoing sealing of surfaces in Hamburg this will lead to increased runoffs of rainwater.

Heavy rain will then increasingly lead to overloads of the sewer with flooding of basements, areas and roads as the consequence. In addition, there will be an increased hydraulic and contaminant pressure on Hamburg waters from the discharge of precipitation water from housing and transport areas and thus will cause a deterioration of the water body. Apart from the dangers of flooding considerable damage to objects and waters will occur.

Nature-oriented water cycle

With increasing surface sealing mankind is changing important basics of the water cycle. Rainwater which should seep away into the ground and evaporate over the plants actually flows off over the surface. However, the existing infrastructure to derive these quantities of water is reaching more and more the limits of its capacity so that flooding of basements, streets and land, as well as additional water pollution may be the results.

Water protection

The protection of waters has special significance for Hamburg. Elbe, Alster and the many other rivers, canals, waterways, streams and ditches dominate the skyline and are of key importance for the quality of life in the green metropolis on the waterfront. Simultaneously, streams and ponds provide important habitats for animals and plants - their protection is therefore of great importance. As required by the EU Water Framework Directive (EU-WFD) and the German Water Law the waters must be managed so that the avoidable impairment of their ecological functions will be omitted.

Flooding and flood protection

With climate change, new challenges approach us which we have to face now. This applies not only to the dangers of rising sea levels. Climate studies for northern Germany show that weather extremes will be more frequent, and that we can expect more severe flooding coming from inland in the future. To reduce the risk of flooding from storm surges and inland flooding is the objective of the EU Flood Risk Management Directive (EU-FRMD).

The changing conditions of a growing city and the consequences of climate change require new ideas and concepts for dealing with rainwater in Hamburg. An integral and interdisciplinary approach to problem solving is required to meet the new challenge for the water industry.

The currently functioning infrastructure of the city needs to be adjusted but an expansion of the existing water and sewage network is not possible in any way. Solutions might lie in, among others, decentralised approaches that do not meet the current standard solutions. Moreover, the resulting problems can only be tackled together with the various institutions of the city. RISA is a working panel in which different subjects and topics are merged and the extensive and demanding tasks are processed together.

The four working groups of the RISA project assure the interdisciplinary processing of tasks around the topic 'Sustainable Rainwater Management':

1. The working group 'Urban Water Management' deals among other things with the issues of hazard analysis and flood detection as well as with potential analyses for decentralized rainwater management.
2. The working group 'Urban and Landscape Planning' analyses primarily options to better involve the water management in the planning process and identifies different options for fixing water management activities in zoning plan procedures.
3. The working group 'Transport Planning' studies, for example, options for the targeted use of roads as 'emergency waterways' during overloads of the sewage system due to heavy rain.
4. The working group 'Water Planning' elaborates, amongst others, water economy balances and develops a catalogue of suitable policy measures to improve water quality.

From the survey, description and analysis of the current situation, the shortcomings and potentials will be shown in comparison with a yet to be defined target state, and adaptation and improvement suggestions will be compiled in the fields of action flood protection, water protection and nature-oriented water cycle. The overarching linking topics in the areas of technical basics, rates & financial models, institutions & legislation, communication & the public are dealt with in additional working groups. The results are brought together in a "Structure Plan Rainwater" which shall be the binding guideline for the actions of management, planners and citizens in Hamburg. The "Structure Plan Rainwater 2030" and its accompanying documents are available for download.