Population: 3.7 million
Berlin is the capital of Germany and the most populous city in the European Union. Among the city's most important topographical features are the many lakes in its surrounding area. Despite this, the Berlin area is one of Germany's regions with the lowest precipitation, a situation that is likely to be exacerbated by ongoing climate change. At the same time, the city is also challenged by extreme heavy rainfall events and very limited capacities of storage sewers and stormwater overflow basins. Increases in sealed surfaces exacerbates this challenge and reduces the relative contribution of groundwater to the lakes and rivers (IGB, 2021). In smaller urban watercourses in the city, there is a high proportion of treated wastewater, which can affect environmental quality, aquatic biodiversity and ecosystem services (IGB, 2021).
Berlin has implemented a number of regulatory and economic instruments and established a Rainwater Agency to address these issues. The aim is to implement sustainable and climate-adapted rainwater management, with a focus on retaining rainwater on the land and reserving physical areas for flooding. This includes a step-by-step decoupling process from the combined sewer systems towards a coupling of green, blue and grey infrastructure. A key component of this process is the identification of suitable nature-based solutions for the areas prone to flood events, which also fit with the given socio-ecological infrastructure.
Population: 633 471
Rotterdam is the second largest city in the Netherlands. Situated in South Holland at the mouth of the Nieuwe Maas channel leading into the Rhine–Meuse–Scheldt delta at the North Sea, Rotterdam is Europe’s largest seaport, which is a major logistic and economic centre. Built mainly behind dykes, large parts of Rotterdam are below sea level, with the lowest point 6.76 metres below sea level. Despite this, through a sophisticated system of canals, dams, and barriers, Rotterdam remains an economically advanced industrial hub with a state-of-the-art water management system.
Water quality has been an important pillar of Dutch regulations and since the 1970s numerous sewage treatment plants have been built to protect the quality of surface-water of lakes, rivers etc. Wastewater is treated then discharged into the Nieuwe Maas River. With large parts lying below sea level, Rotterdam has extensive flood protection infrastructure, but with the growing demands of climate change, improvements are necessary for adaptation.
Rather than approaching climate change as a threat, Rotterdam authorities see it as an opportunity to develop sustainable and resilient water management pathways that can withstand rising sea levels, increases in cloud bursts, extremes in river water levels, longer periods of drought and higher temperatures.
Population: 1.6 million
Barcelona is a city on the coast of northeastern Spain. Situated between the Mediterranean Sea and the Collserola mountain range, the city has a long history extending back at least 2,000 years and a multi-layered identity as both the capital of Catalonia and Spain’s second largest city.
The quality of rivers and waters in Barcelona has improved since the beginning of the 2000s and has stopped progressing ever since. The ecological importance of the river Llobregat, which lies to the south of Barcelona and covers about 100 square kilometres, cannot be understated. Despite its very close proximity to the city, it constitutes one of the most valuable natural areas of the region. The wetlands arе of international importance for aquatic and wildlife ecosystems and are one of the most important freshwater resources for the Barcelona area, forming an underground source with a capacity of 100 million cubic metres of water.
Barcelona’s sewer system is connected to wastewater treatment plants and is enhanced with a number of large underground stormwater reservoirs. It has adopted decentralised, small-scale solutions to drainage such as Sustainable Urban Drainage Systems (SUDS). Barcelona’s push towards more sustainable solutions has been substantial in the last few years and is a response to growing concerns of climate change induced events.
Population: 584 028
Sheffield is a city in South Yorkshire, England. The city is surrounded by seven hills and the confluence of 5 rivers: the Don, Sheaf, Rivelin, Loxley and Porter. Sheffield is known for its greenery with an estimated total of over two million trees, the city has more trees per person than any other city in Europe.
Historically known for its crucial role in the Industrial Revolution, today Sheffield’s wetlands have undergone extensive improvements, resulting in a substantial increase in biodiversity despite the growing urbanisation. Sheffield’s waterways still provide valuable green corridors for wildlife, and following the improvement of Sheffield’s river systems, now support a plethora of aquatic and wildlife species. Over the last 25 years, efforts from industries to control the release of waste into rivers has improved the ecological state of these water bodies with a decrease in ammonia levels and increase in dissolved oxygen.
Blackburn Meadows, situated on the outskirts of Sheffield, is an area where the main sewage treatment works for the city are done. It was created in 1884 due the growing pollution in waterways at the time and is operational to this day. There have been upgrades to the plant throughout the years with a more recent incentive to further improve its sustainability capacity. Climate change presents a challenge for Sheffield’s sewage system so a change towards a more sustainable way of wastewater management is necessary.
Population: 689 326
Boston is the capital and most populous city of the Commonwealth of Massachusetts in the United States. Situated in the region of New England and on the Atlantic coast, Boston is consistently ranked as one of the most green cities in the United States.
With its proximity to the Atlantic ocean and to the Boston Harbour Islands, as well as the Charles River that flows through the city, Boston is responsible for protecting various ecosystems - both aquatic and wildlife - so as to ensure their ability to thrive and be minimally disturbed by urban activities.
Boston’s water, sewer, and stormwater are managed by the Boston Water and Sewer Commission (BWSC), which maintains and improves the quality and reliability of water, sewer, and stormwater systems in the city. Boston is home to New England’s oldest and largest water, sewer, and stormwater systems that take 70% of the total land area of the city. The system consists of both separated and combined wastewater collection methods, the latter having the dual function of transporting sanitary flow together with stormwater runoff in one conduit. This type of system is common in older cities. Therefore, improving the sustainability of sewer systems in Boston is of central importance for ensuring its water ecosystems can flourish.