Nature conservation for flourishing cities

THE world’s great cities could hold the key to prosperity. Yet a new study has shown a worrying trend: the water they need to grow is getting more expensive due to failure to protect the natural forces that purify it.

Cities are amazing engines of productivity. As hubs of our modern societies, they mix people with a diversity of skills and create fertile ground for learning and invention.

In many respects, bigger tends to be better. Larger cities have more patents and inventions per person, and achieve better energy and resource efficiency thanks to economies of scale. For example, they require less conducting cable per person to carry electrical power.

Concentrating people in cities also leaves more space for nature.

Paul Romer, recently appointed World Bank chief economist, has been championing the idea of charter cities — new cities we could build to experiment with large-scale innovations in technology or government.

Dozens of such cities could help us explore more sustainable ways of living, and help meet the housing needs of the additional 3.4 billion people expected by 2050.

It turns out, though, that protecting nature is crucial for cities to work.

Any city draws its clean water from a natural watershed area — some nearby, others farther away.

The rain that drains into an area is filtered and purified by natural land cover — forests, marshes and grasslands — before entering as the “raw water” of treatment facilities. New York City’s water, for instance, comes from big reservoirs about 160km away in upstate New York.

As cities have grown, their watershed land has been cleared to make way for housing, factories and agriculture. As a result, water quality has declined.

Agricultural runoff, for example, boosts concentrations of nitrogen, phosphorous and sediment. Treatment centres must then remove these impurities, requiring the use of increasingly complex and costly technologies.

A new study, led by ecologist Robert McDonald of the Washington-based Nature Conservancy, suggests that the cost of water treatment is becoming a heavier burden globally.

Looking at changes from 1900 to 2005 in the watersheds of 309 large cities, all home to more than 750 000 people, the study found that more than 90% suffered degradation and nearly a third experienced a significant rise in treatment costs, many by more than 50%.

The study confirms what environmental economists previously only suspected: loss of natural water-purification capacity is systematically pushing up the cost of treatment around the globe.

The best estimate puts the added expense at more than $5-billion (about R67-billion) a year. And it’s set to get worse. Watershed degradation is expected to become more severe in the next decade or so with more land being farmed.

By 2030, global fertiliser use is expected to rise nearly 60%.

The lesson is that our cities need concerted investment in watershed preservation.

Water treatment is becoming a heavier burden

The good news is that this need not be terribly expensive. Targeted projects can make a big difference.

Since 1997, for example, New York City’s environmental protection department is taking care of more than 53 000ha of valuable watershed and its water-treatment costs are now far lower than those of other US cities.

New York’s forward thinking can and should be replicated globally. McDonald and others estimate that roughly one in four cities — home to about 800 million people — could reap a positive return on investment aimed at conserving watersheds.

So it is something worth doing, and it would be an important step towards securing the sort of environment we need to survive. — Bloomberg