BlueSCities Challenges



According to the United Nations (UN) there are currently 23 Mega cities (metropolitan areas with a total population in excess of 10 million people), 40 cities with 5 to 10 million inhabitants and 394 cities with 1 to 5 million inhabitants (UN 2012). Currently 52 % of the human population lives in cities, and by 2050 this will be 67 %. In developed countries this will even rise to 86 % by 2050 (UN 2012). Urban areas in the world are expected to absorb all of the population growth over the next four decades. Most of the population growth expected in urban areas will be concentrated in cities and towns of less developed regions (UN 2012).

  • Challenges related to water and climate change

With rapid population growth, water withdrawals have tripled over the last 50 years and are predicted to increase by 50% by 2025 in developing countries (SIWI 2012; UNESCO 2012). Competing demands for scarce water resources may lead to an estimated 40 % supply shortage by 2030 (2030 Water Resources Group 2009). Recently, the World Economic Forum (2014) identified the water supply crisis as one of the top three global risks. Furthermore, a recent report from the European Environment Agency (EEA, 2012) on urban adaptation to climate change in Europe described many challenges and opportunities for cities together with supportive national and European policies.

  • Resources, waste and the need for resource recovery

According to the UNEP (2013), at the start of the 21st century, total raw material extraction is estimated to have been between 47 and 59 billion metric tons per annum. Between 1900 and 2005, global material resource use increased by a factor of 8, almost twice as fast as the rate at which the global population grew. Construction materials increased by a factor of 34, while industrial minerals and ores grew by a factor of 27 and fossil fuels grew by a factor of 12. Despite a fourfold increase in population over the period, biomass extraction only increased 3.6 times. Average per capita resource consumption  around  the world  is  currently  around  8  tons  per  annum,  about  22  kg  per  person  per  day;  extraction increases to about 40 kg of resources per day. These global figures, the projected global population growth and the change in consumption patterns lead to: (1) resources reduction, (2) recycling of solid waste and (3) circular economies. Waste can be categorized into organic waste, for instance wastewater and inorganic solid waste such as packaging and consumer goods. The organic waste can be efficiently handled as illustrated by the HAMBURG WASSER (van Leeuwen and Bertram, 2013). Efficient management of the inorganic waste involves an increased level of recycling and material recovery and requires the coordinated action of authorities and the collaboration of citizens to adjust their behaviour.

Costs of city infrastructures

A recent UNEP (2013) report on city-level decoupling with the focus on urban resource flows and the governance of infrastructure transitions provided shocking figures and a clear warning on the needs and the spending of money related to the infrastructures in cities at the global level: “a total of US$41 trillion is required to refurbish the old (in mainly developed country cities) and build new (mainly in the developing country cities) urban infrastructures over the period between 2005 and 2030.

Infrastructure Costs (in trillion US$)
Water systems 22.6
Energy 9
Road and rail infrastructure 7.8
Air- and sea-ports 1.6


Expected costs for city infrastructures over the period 2005-2030 (UNEP, 2013)

The report also warns that “Sooner or later, the money needed to modernize and expand the world’s urban infrastructure will have to be spent. The demand and need are too great to ignore. The solutions may be applied in a reactive, ad hoc, and ineffective fashion, as they have been in the past, and in that case the price tag will probably be higher than US$40 trillion. After all, infrastructure projects are notorious for cost overruns. But perhaps the money can be spent proactively and innovatively, with a pragmatic hand, a responsive ear, and a visionary eye. The potential payoff is not simply the survival of urban populations, but the next generation of great cities.”