From Science Alert (David Nield):
Groundwater – fresh water cached underground in soil and between rocks – takes much longer to respond to temperature changes than surface water, the researchers point out.
We rely on rain to keep groundwater stocked up, which means areas seeing hotter weather and less rainfall are going to be lighting the fuse for a future ‘timebomb’ in which water supplies can’t keep up with demand. The time delay potentially makes these ‘hidden’ shortages even more dangerous.
“Our research shows that groundwater systems take a lot longer to respond to climate change than surface water, with only half of the world’s groundwater flows responding fully within ‘human’ timescales of 100 years,” says one of the team, Mark Cuthbert from Cardiff University in the UK.
“This means that in many parts of the world, changes in groundwater flows due to climate change could have a very long legacy. This could be described as an environmental timebomb because any climate change impacts on recharge occurring now, will only fully impact the baseflow to rivers and wetlands a long time later.”
In areas more sensitive to climate change – so wet and humid spots like the Amazon and central Africa – the effects on groundwater could be seen within just 10 years, the new study says. In dry and arid regions it could take much longer.
Using readings taken in the field as well as data models, the team estimated that for nearly half the groundwater supplies on the planet, it might take 100 years or more to for levels to replenish or become balanced again.
In some places – such as under the Sahara – we know that groundwater supplies are still responding to climate change 10,000 years ago, when the area was much wetter.