Increasing numbers of cities worldwide risk reaching Day Zero, with taps running dry, and exacerbating the effects of climate change, unless they start actively managing and improving the resilience of their entire water basins, warns a new report by global engineering consultancy Arup.

Cape Town’s recent water crisis has alerted major cities to threats to their water supply. According to the Arup report Cities Alive: Water for People, endorsed by the International Water Association (IWA) and launched at the IWA World Water Congress & Exhibition in Tokyo, cities need to expand what they might now consider ‘their’ water infrastructure to include the entire river basin on which they depend.

Introducing the report, Dr Mark Fletcher, Global Water Leader, Arup, said:

“One in four large cities are already facing water stress, and demand for water is only projected to increase.

“Growing urban populations the world over are inexorably driving this rising demand for water. Concurrently, changing climate is driving extreme events in cities, from drought to floods, resulting in severe economic outcomes. As a result our urban water infrastructure requires extensive renewal and expansion.”

According to the report, it is estimated that between 1.6 and 2.4 billion people live in river basins that already experience water scarcity. This is expected to almost double by 2050 to between 3.1 and 4.3 billion people from population increases alone, regardless of climate change exposing further basins to water scarcity.

It also refers to a projection by the United Nations Environment Programme that if efficiency does not improve, by 2030 worldwide water demand will outstrip supply by 40%.

The report highlights that the world’s 100 largest cities occupy less than 1% of the planet’s land area, whilst the basins that provide their water resources cover over 12% and serve almost a billion people. Water basins are vital for supplying cities with water, collecting all the surface water and groundwater in the area. Cities impact stewardship for hundreds of miles. They have the potential to influence how their water basins are managed, yet they invest very little in them.

Water in cities should be seen as a connected network of ‘blue infrastructure’

According to the report, rethinking water in cities as a connected network of ‘blue infrastructure’ (especially in combination with ‘green infrastructure’) offers environmental, social and economic benefits.

The report is calling for more ‘upstream thinking’ in how cities approach water management. This means greater collaboration, working with landowners, businesses and local authorities further upstream to consider the water basin as a whole and understanding how it behaves.

The Arup report outlines recommendations for successfully managing and maintaining water basins, including:

Working together - City governments, businesses and water organisations should be working with land owners and land managers further upstream to reduce flood risk, improve water quality and encourage more sustainable water sources.

Working with nature - All basins are different; cities need to understand the flows of water, sediments, nutrients and ecology of their basins, to formulate and provide successful designs and solutions, such as Natural Flood Management (NFM).

The Leeds Flood Alleviation scheme in the UK, for example, was developed after Leeds experienced widespread flooding for a number of years, most recently in 2015. It took a basin-wide approach in implementing landscaped natural flood defences (NFM), and adjustable weirs to improve water continuity. The scheme now protects 500 businesses and 3,000 homes. It has also provided new city spaces.

Similarly in China, the Sponge City Programme implements NFM by using greenbelt, rainwater gardens, permeable paving, rainwater harvesting and detention ponds to combat serious flooding.

Urban water resilience is not possible without rural water resilience

Mark Fletcher continued:

“Recognising the importance of the entire water basin is essential as urban water resilience is not possible without rural water resilience. In simple terms, we must be more water-wise. With up to 4.3 billion people expected to live in cities by 2050, this is something city leaders and water managers need to be looking at now. Whilst this is a challenge, it also provides a significant opportunity to revolutionise how urban water systems are designed and retrofitted, and how they can deliver greater benefits for all.”