More than half the world’s rivers stop flowing for at least one day per year, according to the first detailed global map of river flow. More rivers than that are expected to run dry if climate change and water management issues aren’t addressed.
Many rivers and streams have natural disruptions to their flow – for example, Himalayan streams that freeze solid in winter and Saharan rivers that dry up for long stretches between rainy seasons. Others sometimes dry up when too much water is extracted for crop irrigation or other human uses.
To find out how many rivers have intermittent flows, Mathis Loic Messager at McGill University in Canada and his colleagues analysed data from 5600 global river flow measurement stations. Next, they used machine learning to predict the probability of intermittent flows along the rest of the global river network, based on each section’s climate, soil, geology and other environmental factors.
From this, they estimated that water ceases to flow for at least one day per year along up to 60 per cent of the world’s 64 million kilometres of mapped rivers and streams.
Even more rivers could start to run dry in the future as climate change drives more severe, frequent droughts in some regions, says Ton Snelder at LWP, a water management consulting firm in New Zealand, who co-authored the study.
This could be exacerbated by disagreements over how to allocate river water, he says. “There are conflicting values about how to use water resources in pretty much every country in the world,” he says.
At the same time, global warming may cause some naturally intermittent rivers to start flowing continuously. For example, rivers in usually cold climates may freeze over less, says Snelder.
These changes to river systems could affect biodiversity, he says. “The balance may shift in favour of some species and push others to local extinction.”
More rivers drying up could also make it harder for some communities to access enough water for drinking, farming and other important uses, says Snelder.
The researchers hope the study will allow changes to river flows to be better monitored in the future and improve regulation of rivers, for instance by avoiding taking too much water from rivers with intermittent flows.
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