Ecosystems / Water
Water is a necessity for life. Yet, though life first evolved in the oceans, most terrestrial organisms cannot drink the salt water that makes up over 97 per cent of the world’s total. Of the fresh water that makes up the rest, more than 90 per cent is locked away in glaciers and ice sheets, or hidden deep underground. Only 0.0001 per cent of fresh water is easily accessible; human settlements are clustered along the waterways and fertile floodplains.
This is all the fresh water available to us. It is not created anew but recycled, as the sun evaporates the oceans and water falls back to earth as rain and snow. What we drink is made up of ancient molecules of water that have fed rainforests, slaked the thirsts of dinosaurs and prophets, spent millennia frozen in glaciers. There is enough water in total for us all, but it is unevenly distributed. While the rich world uses more and more, many countries, particularly in Asia and Africa, suffer shortages. A third of the world’s people live in dryland regions that have access to only eight per cent of the world’s renewable water supply.
For centuries humans dumped waste in the nearest watercourse and drank from it too, but this works only when the waste is small and the people are few. The pollution of waterways by toxic industrial waste and sewage is one of the biggest environmental challenges of our time.
Modern improvements in human health are largely due to great public municipal works of sanitation that provide people with clean drinking water. Access to clean water is still one of the major distinctions between the world’s ‘haves’ and ‘have nots’. The wars of the future are likely to be over fresh water – and sooner than we think.
Meanwhile, as the Earth heats up and the polar ice caps melt, the rising, warming oceans are washing inland, salinizing freshwater tables and flooding human settlements. The oceans are the engines of global weather systems: as they warm, they are not only killing whales and coral reefs, they are triggering storm surges, droughts and new unpredictable weather patterns right across the planet.
WATER – THE FACTS
• In some regions, such as the Middle East and North Africa, humans use 120% of renewable water supplies, due to the reliance on groundwater that is not recharged.
• Between 1960 and 2000 the storage of water in reservoirs quadrupled, so that the amount of water now stored behind large dams is estimated to be 3-6 times the amount held by natural river channels (excluding natural lakes).
• The construction of dams and other structures along rivers has affected flows in 60% of the large river systems of the world. Water removal for human uses has reduced the flow of several major rivers, including the Nile, Yellow and Colorado Rivers, to the extent that they do not always flow to the sea.
• As water flows have declined, so have sediment flows, which are the source of nutrients important for the maintenance of estuaries. Worldwide, sediment delivery to estuaries has declined by roughly 30%.
• Since about 1980, approximately 35% of mangroves have been lost, while 20% of the world’s coral reefs have been destroyed and a further 20% badly degraded.
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