WWF: In water crisis, cities play starring role

The world is rapidly urbanizing, and cities have a key role to ensure the protection and restoration of ecosystems that they heavily depend on, the World Wildlife Fund says.

Writing in a new report entitled "Big Cities, Big Water, Big Challenges," the WWF says the emergence of megacities and metacities -- metropolises with more than 10 million and 20 million residents, respectively -- has an outsize effect on water supplies, forcing cities to reduce water consumption, recycle wastewater, restore adjacent watersheds and improve engineering solutions for water supplies.

The authors write:

The adoption of a multi-sectoral approach to water and wastewater management at the national level is a matter of urgency. This approach should be implemented by incorporating principles of ecosystem-based management extending from the watersheds to the sea, and connecting sectors that will reap immediate benefits from better water and wastewater management.

So what's the problem? As the world moves downtown, the flow of ecosystem services into the city is increasing faster than the population is growing. That's unsustainable, and compounding the problem is that most cities do not fully comprehend their "water footprint," or catchment area -- the complete network of natural resources that supply the city.

At the forefront of this are megacities, the largest offenders of water overuse. When too much groundwater is removed from aquifers, pore pressure drops and aquifer compression results, which can lead to land subsidence -- literally, the sinking of the ground. (For coastal areas, that's an especially pressing concern.)

And that doesn't even mention the downstream effects of abstracted surface water.

Take Mexico City -- population proper 9 million, metro population 21 million --for example:

In Mexico City, over-exploitation of aquifers has contributed to the continued subsidence (five-40 cm per year), increasing the chance of catastrophic flooding.The dependence on distant water supplies has resulted in social and environmental conflicts with communities in the donor basin; in addition to the high energy costs(0.6% of the country’s total electrical energy generated) associated with pumping water over 1000 meters in elevation and 150 kilometers away

It continues on every continent. Buenos Aires' rivers are referred to as "open sewers;" Nairobi's sanitation situation is deplorable; Karachi discharges 80 percent of its untreated wastewater into the Arabian Sea; Kolkata can't properly maintain its own aging infrastructure; Shanghai's drinking water is threatened by saltwater intrusion.

For cities to be sustainable, reliable access to safe drinking water and adequate sanitation are the first steps; but awareness, law enforcement, water reuse, corporate stewardship, economic incentives and climate change adaptation plans are all pieces of the puzzle.

But cities must first understand their risk. To do so, governments must conduct comprehensive regional and local analysis to properly evaluate future water availability, precipitation, drought, runoff patterns, sea level rise, and flooding risks, the WWF says.

The authors, again:

More informed political and financial decisions can be made with access to more diverse information about risks and probabilities. By considering a range of risks, local efforts provide better opportunity for effective long-term adjustment and management.

The good news? "Urbanization is not per se bad for ecosystems," the WWF assets, and many ecosystems in and around urban areas deliver more environmental services -- food, water, and so forth -- than agricultural systems.

But beyond all that, density keeps risk at bay: since urban areas occupy just 2.8 percent of Earth's total land area, the impact of human settlement is concentrated.

Photo: WWF-Canon/Mauri Rautkari

This post was originally published on Smartplanet.com