City planners in Berlin, Germany, expect heat waves and rainstorms to become common in northern Germany as climate change deepens. They plan to transform the city by making it into an “urban sponge,” with green roofs and wetlands to ensure heat and flood-proofing the city.
The plans include more trees and sidewalk awnings to provide shade; living rooftops covered in moss and grasses; light-coloured buildings that reflect rather than absorb heat; special heat-resistant road surfaces to prevent tarmac melting on very hot days; urban wetlands and more permeable surfaces to absorb and store water during heavy rainfall.
Climate changes will hit some countries much harder than Germany, but northern Europe won’t be exempt from tough impacts. As global warming gathers pace, heat waves and flooding are expected to be commonplace.
Part of the city’s strategy climate strategy is to make redesign the cityscape as a water-sponge.
“We’ve been using the term ‘Stadtschwamm,’ or ‘sponge-city’,” Heike Stock, the municipal official in charge of the program.
“The key is to avoid sealing up too much of the ground surface with concrete or tarmac. Wherever possible, we want water-permeable surfaces. For example, parking areas and median strips can be resurfaced to allow water absorption into the ground.”
Building owners are encouraged to “regreen” the inner courtyards typical of Berlin apartment buildings. Rooftops planted with mosses or grasses can also absorb water, and then release it through evaporation later on. That results in an evaporative cooling effect, in the same way that sweat evaporating from the skin cools an overheating athlete.
Building owners are encouraged to “regreen” the inner courtyards typical of Berlin apartment buildings.
The goal is to retain rainwater within the cityscape, so that part of it evaporates and the rest of it releases gradually, rather than in an abrupt rush, into Berlin’s rivers and lakes.
The city’s plans are recommendations and don’t have the status of regulations and are not binding on developers.
“The city will use its powers to negotiate agreements with real estate developers over the details of projects subject to planning permissions to encourage climate-adaptive features like green rooftops,” she said. “We really want to avoid new buildings that aren’t adapted to a hotter climate, which would result in people installing electricity-hungry air-conditioning units during summers in future.”
In addition, green building design competitions, citizen engagement strategies such as the city’s existing, very successful tree-planting sponsorship programmes, and various subsidy programs will help encourage take-up of the recommended design features.
Retrofitting is a key part of the strategy. The city wants to prevent urban sprawl. That means further increasing the density of residents per square kilometre.
Given that most of the city’s land already has high-density buildings or roads on it, most of the opportunities will lie in retrofitting existing buildings.
“In cases where a building’s roof is getting tired and needs to be replaced anyway, it can be a smart business move to replace it with a combination of solar panels, planted green surfaces, and a deck accessible to the residents,” Stock said. “That enhances the value of the property and makes it more attractive to renters or buyers.