environment sustainability

Why do cities experience water shortages?

Over the last year or so there have been several notable news stories about water shortages. The most severe is the situation in Cape Town, which has been living with , when the taps run dry. Nairobi is , holding out for a decent rainy season to top up the falling water levels at the dams that supply the city. Last year California finally saw an easing of drought conditions after several dry years, though it looks like

There are several factors that combine to cause this kind of stress on water systems. It’s worth looking at them, because this a growing problem. Pressure is mounting on fresh water, which is one of the nine planetary boundaries. In a changing climate, cities that haven’t historically experienced water shortages might face new challenges.

The first factor to consider growing urbanisation. It’s been around a decade now since the world crossed that symbolic line where more people lived in cities than in rural areas. There are sustainability advantages to cities in some contexts, but where a lot of people are all in one place, a lot of water is needed in that place too. Urbanisation concentrates water demand – the same number of people spread out across a whole region might not experience water shortages. Put everyone in one place, and water supply is much more difficult. This is why England has occasional droughts, despite its high rainfall – the water just isn’t where the people are.

A second factor is population increase. Whether they are born in the city or moving in, every extra person adds their water needs for drinking, washing, laundry and everything else. Populations are rising in all three of the examples above, to one degree or another. If the population is growing rapidly, the city ends up in a chase to keep ahead of water use, with constant demand for new infrastructure and more water sources.

Third, as countries develop and incomes grow, people use more water. As Frank Trentmann describes in his book Empire of Things, consumerism arrives with running water. Expectations rise and social norms change. People will wash every day, where earlier generations had a bath night once a week. When you get a washing machine, you might do laundry two or three times a week. Rising water demand from those on the lowest incomes is a sign of real material progress, so this is a good thing – up to a point.

Finally, there’s the wild card of climate change to deal with. As the world warms, some areas are going to experience more droughts, while others are going to see an increase in rainfall. Part of the problem is the unpredictability. Both Cape Town and Nairobi store water in the rainy season to use throughout the year. California gets a third of its in the Sierra Nevada mountains. Cities build their infrastructure around these regular precipitation patterns. When climate disrupts those patterns, water supplies are threatened.

Climate change also drives extreme weather. A region might receive the same amount of rain, but in larger storms. Too much at once can overwhelm water management systems, and do nothing for long term supply. Remember the flooding in Houston less than a year ago? at the time of writing, despite that catastrophic deluge.

There are other factors of course. Much of it has to do with geography, and there are some important cities that really have no business being where they are. There are kinds of ways to supply water, from rainfall, rivers, aquifers or desalination. There’s the competence and budgets of local planners to consider, the ability to fund and to deliver infrastructure projects. Aging infrastructure is a big concern in California. Behaviour matters too. Some places have been able to incentivise or enforce good water stewardship, and some haven’t – Californians’ as soon as the worst was over.

Every city is different, but the underlying trends are often the same. And as the climate is destabilised, we’re going to be hearing more stories about water crisis.

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