Water, Megacities and Global Change: Portraits of 15 Emblematic Cities of the World

Emblematic megacities address the threats of climate change to their water-related needs

By 2030, over a billion people will live in approximately 100 very large cities and 60 % of the world’s population will live in urban areas. Sustainable water management is particularly challenging in these large urban centres, or megacities*, which are exposed to extreme risks in terms of the negative impacts of climate change on water and sanitation infrastructure and services. A new publication, launched during the Habitat III conference in Quito, Ecuador, draws portrait of 15 emblematic megacities, their unique circumstances and how they are addressing shared water governance challenges. The publication “Water, Megacities and Global Change”, co-edited by UNESCO and ARCEAU-IdF, is simultaneously the result of concrete scientific presentations and a call for general mobilization to devise the sustainable urban policies the world needs**.

In 1970, the United Nations identified three megacities. This number rose to 10 in 1990 and 28 in 2014. According to projections, there will be 41 by 2030, many located in the world’s least developed countries. Throughout history, these cities have often lacked both the time and the means to develop their urban services, including those relating to access to water, sanitation and rainwater drainage. This situation creates profound vulnerabilities and complex challenges. It is crucial that megacities share their experiences, so as to develop services capable of meeting the expectations of their inhabitants.

“This book marks an important phase in the creation of an alliance of megacities focused on water-related issues in the face of climate change” explains UNESCO’s Director General, Irina Bokova. “Megacities embody the principal of ‘creative constraint’, whereby infinitely complex situations engender the mobilization of an incredible number of talents, experts and initiatives to provide solutions. In this new era of limited resources, human ingenuity and respect for each other’s dignity represent our ultimate renewable resources. We need to free their potential.”

While they face shared challenges, their characteristics and histories are very different. The oldest cities, such as Istanbul, London, New York and Paris, were often the first megacities, and have a long and rather slow history of immigration and settlement. They inherited a system that incorporates assets aged are over 100 years old which they have gradually been able to scale up. In Istanbul, the 190 km Grand Melen transmission line is a contemporary version of a 240 km Roman waterway.

New megacities, such as Buenos Aires or Beijing, have experienced expansion that is very recent and very swift, resulting in infrastructures of historic centres that differ from those of recently urbanized areas. Generally, rapid population growth places pressure on the oldest systems of the city centre and tests the reliability of municipal services, including the water delivery system.

Meeting the demand for drinking water is yet another challenge for several of the megacities presented here. In Mumbai, the distribution system is almost non-existent in slums, which host 56% of the city’s population.

“Each of the megacities in this publication has specific local conditions characterizing their geographic, climatic, hydrogeologic, demographic and economic situations. However, they also share similar water governance challenges with multiple actors” explains the President of ARCEAU-IdF, Jean-Claude Deutsch.

With this in mind, a new Alliance was launched during the Eaumega2015 Conference by its organizers: UNESCO’s International Hydrological Programme(IHP), the Alliance of Water Stakeholders from the Paris Region(ARCEAU-IdF), and the Global Association of Local Governments Addressing Sustainability (ICLEI). The Alliance is creating an International Platform for Cooperation to facilitate a dialogue on water, though which Megacities will learn from each other’s experience, exchange best practices, partner with appropriate technical, academic, and financial institutions, as well as design and implement their individual responses to the challenges of climate change. This publication is one of the building blocks of the platform.

  • Urban centres with over 10 million inhabitants

** Beijing, Buenos Aires, Chicago, Ho Chi Minh City, Istanbul, Lagos, London, Los Angeles, Manila, Mexico City, Mumbai, New York, Paris, Seoul, Tokyo