Planetary boundaries 4 – water

earthIf you missed them, here’s are the first few parts of this series: Introduction, Week one: ozone, Week two: nitrogen, Week three: chemical pollution

This week we come to the fourth planetary boundary, fresh water. The first thing to say about water is that we can’t run out of it. It cycles around through evaporation and precipitation, melts and refreezes, runs from gutters to rivers to seas. It can’t be used up, just moved around, but we can move so much of it around that it disrupts natural systems and becomes a serious environmental problem.

The place where human intervention is most obvious is in rivers. 25% of major rivers now dry up before they reach sea, which affects fish and wetlands areas as well as depriving communities downstream. Since wetlands play an important part in cleaning water and are major wildlife hotspots, drawing too much from a river can affect the pollution and biodiversity boundaries too.

You can lose a river by using too much of it for industry, irrigation, or for domestic use. As Mark Lynas writes, the Colorado River was powerful enough to carve out the Grand Canyon, but it we’ve still managed to use all of it. It no longer reaches the ocean, vanishing instead into “an enormous plumbing works” serving the people of Las Vegas, LA and Phoenix.

The other way to mess with a river is through dams. They’re very useful things, dams, allowing us to redirect enormous quantities of water and generate electricity in the process. Hydro power can deliver renewable energy on a scale that nothing else can, by some distance. But dams are also controversial, requiring vast capital, dislocating communities and flooding their lands, and radically changing local ecosystems. There are dams on 60% of the world’s big rivers, and an estimated 800,000 dams worldwide. China, which until recently had a water engineer as head of state, has been a particularly big fan.

There are consequences to bottling up a big river. It breaks the pattern of seasonal water flows and confuses fish spawning. Nutrient-rich silt builds up in the dam instead of running downstream and feeding the waters and the sea, affecting aquatic and marine life potentially hundreds of miles away. When water flow is significantly reduced or a river dries up entirely, whole species will lose their habitats, including fish, amphibians, crayfish and birds.

The impacts on human activity can be severe too. Those downriver can lose water that they previously used on farms, affecting food production. River transport networks are lost, and water may become expensive or subject to shortages. At its worst, this can lead to desertification, empty lakes, and ghost towns – the Aral Sea being the most dramatic example. Where communities are displaced, this can create refugee and migration issues. It can also feed conflict. You may have read about the war of words between Egypt and Ethiopia in recent weeks.

All of these are local problems, but they add up to a planetary boundary because it is possible to accidentally drive much larger scale change. The aggregate effect of major damming and irrigation could change rainfall patterns, including regional monsoons. When combined with climate change, that really does become a matter of global scale resource management.

The good news is that we are currently within the safe operating limits on fresh water. There is room to expand a little, which is just as well given the rising demand for water to feed a growing and industrialising population. But as we use more, water resources will tighten, and that means we need to be smarter about where and how we use it. If we don’t, the slack will soon be gone. The Water System Project, set up to look into this problem, estimates that if current trends continue, severe water shortages could affect half the world’s population by 2050.

“This handicap will be self-inflicted and is, we believe, entirely avoidable” says the project, so it’s up to us to manage our water and prevent a future crisis. There are lots of things we can do. We can practice low-till agriculture, which prevents soil moisture being lost into the air, another major source of water loss that I haven’t covered in detail here. Wetlands can be restored, better regulation can prevent freshwater pollution and make sure more of it remains usable. Subsidies for water use can be removed to incentive better water management.

The Sustainable Rivers Project is experimenting with ways to restore river systems in the US, the US Army’s Engineering Corps being a major partner. Rainwater catchment can be scaled up, and irrigation techniques that make the best use of rainwater. Water-free toilets will become more common in some places. Some things, however popular they may be, just need to stop – squandering aquifers to create golf courses in desert regions, for example.

Because of the regional nature of water, it isn’t as if saving water in one continent will free it up elsewhere, but in some regions and river basins that will be the case. On major rivers that run through more than one country, it is crucial that water rights are resolved. There are 19 international rivers that run through five countries or more, and they raise difficult questions – do the rights to the water lie with the source country, or the countries that they pass through? Should downriver countries pay for the water that flows in from another country? Wars will be fought over such questions if they cannot be negotiated ahead of time.

Here’s a useful summary of the problem from the Global Water Systems Project:

Freshwater boundary
Safe limit: 4,000 cubic km a year
Status:  currently safe


  1. In terms of a practical understanding of nature, compared to
    the bees we are but infants. estimates that 40% of rivers and streams
    are unfishable and unswimmable and 50% of lakes and ponds are unfishable and unswimmable.
    The birds are singing, and no traffic can yet be heard.

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