Residents and helpers in North Rhine-Westphalia and Rhineland-Palatinate have to experience the violence with which heavy rain and overflowing streams can flood buildings and entire communities.

The rain came from heaven there so profusely that it could no longer seep into the earth.

The masses of water made their way through the towns, streets were washed away, cellars overflowed.

In such a situation, there is not much that can be done against the water masses at first.

Jan Hauser

Editor in business.

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But how can the municipalities better prepare for future extreme weather? It's not easy, but experts agree that retention and infiltration areas such as lawns on flat roofs and larger drainage channels should be able to mitigate the consequences of heavy rainfall. You have been calling for heavy rain to be included in urban planning for some time. Martin Weyand from the Federal Association of Energy and Water Management (BDEW) criticizes that too many areas are sealed. "We have to rethink and change the infrastructure so that more can seep away," says the managing director for water and wastewater.

Weyand urges a dismantling and demands cisterns that can hold water.

In cities, facades and roofs should be greened and parks and soccer fields should be used in a targeted manner in the event of flooding.

The approval of construction measures should depend on the possibility of infiltration.

In the past few decades, open spaces in Germany have given way to living space and traffic.

The Federal Environment Agency sees important soil functions being lost as a result, especially water permeability and soil fertility.

At the end of 2018, around 45.1 percent of 51,315 square kilometers of settlement and traffic areas in Germany were sealed, which the authority has evaluated using state statistics.

That means: built on, concreted, asphalted, paved or otherwise paved.

In relation to the total area, the proportion of settlement and traffic area was more than 14 percent and the proportion of sealed area was 6.5 percent. At the end of 1992, the proportion of settlement and traffic area was 11.5 percent and the proportion of sealed area was 5.3 percent. The proportion is often higher in metropolitan areas. A study by the insurance industry lists Munich with around 47 percent as the city with the highest proportion of sealed surfaces. Oberhausen, Hanover, Ludwigshafen, Nuremberg and Mannheim also each have more than 40 percent.

Norbert Portz, environmental expert at the Association of Towns and Municipalities, considers the increasing density to be counterproductive - unsealing is the order of the day. He also wants to give the water more space as well as more flood retention basins and mobile protective measures. "The extreme weather as a result of climate change with heavy rain of up to 200 liters per square meter in only a short time shows that there is no absolute protection against isolated natural disasters," he says.

But in order to minimize the damage, urban development and construction planning should take greater account of flood prevention and protection against extreme weather. He calls for green and blue urban renewal: more trees and green spaces and more watercourses. Streams can lower the city temperature by a few degrees. "We have to question the increasing density of inner cities in order to create living space," says Portz. This is because valuable open and retention areas for flood protection were lost.

Berlin already prescribes infiltration areas for building projects. The water companies there have built large pipes underground as storage space. Similar retention basins can be found in new development areas. In old towns, on the other hand, the sewer system is in worse shape and is sometimes burdened by many truck trips. In Hambergen in Lower Saxony, the precautions started after extreme rainfall seven and eight years ago. The community has renewed pipes, built a relief sewer for 300,000 euros and two retention basins for 70,000 euros. The community also advises its citizens to take action: wall up cellar shafts, hold bulkheads, raise driveways and entrances.

From the point of view of the City Day, the cities must continue on the path. “Climate impacts such as heat waves, droughts and heavy rain can no longer be talked about. They are reality, ”says its President Burkhard Jung, Lord Mayor of Leipzig. The cities know that they too must take preventive action against these dangers. The SPD politician speaks of more green spaces, the expansion of retention basins and the renaturation of watercourses. Because climate change is advancing, extreme weather events are to be expected even more frequently in the future.

The German Association for Water Management, Sewage and Waste urges a conversion to a water-conscious city.

This should not only help in the case of heavy rains.

"Water and urban greenery are central components of climate adaptation, for a healthy and livable urban landscape as well as for the preservation and strengthening of biodiversity," says association president Uli Paetzel (SPD), who heads the water management companies Emschergenossenschaft and Lippeverband in the Ruhr area.

Heavy rain and floods required emergency drainage routes.

Green areas, squares and sports facilities should be multifunctional, also usable for short-term retention of precipitation runoff.

In addition, more water-permeable surface coverings, infiltration systems, street and building green are needed.