At a Glance

Scientists say it takes much longer for groundwater systems to respond to climate change.Some systems could take up to 100 years to show impacts from global warming occurring now.

Climate change may be creating a groundwater "time bomb" as the world's underground water systems catch up to the impacts of global warming.

Researchers for a study published Monday in the journal Nature Climate Change say more than half of the world’s — the largest source of usable freshwater in the world — could take more than 100 years to completely respond to current environmental changes from global warming.

primarily by rainfall through a process known as recharge. Concurrently, water exits or discharges from groundwater sources into lakes, streams and oceans to maintain an overall balance.

When there is a change in recharge due to a lack of rainfall, for example, levels of groundwater drop until balance is restored.

The problem facing scientists, government officials and water management planners is knowing exactly when recharge changes occurring now as a result of global warming will be reflected in discharge from groundwater sources into lakes, streams and oceans.

“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," Mark Cuthbert, lead author and research fellow at Cardiff University’s School of Earth and Ocean Sciences and Water Research Institute said in the press release.

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Cuthbert noted 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 time bomb because any climate change impacts on recharge occurring now, will only fully impact the base flow to rivers and wetlands a long time later," he said.

To determine the how long it might take for various groundwater systems to respond to climate change, the researchers used hydrologic datasets coupled with groundwater model results.

They found that locations that are wetter and more humid like the Amazon and Florida Everglades may begin to experience recharge/discharge problems in the shorter term. It would take much longer in arid locations like the Sahara desert.

With more than 2 billion people relying on groundwater as a source of drinking and irrigation water, a delay in reaction to the systems could become very problematic, especially in locations where people rely almost entirely on groundwater for personal, industrial and agricultural needs.

"It is essential that the potential for these initially hidden impacts is recognized when developing water management policies, or climate change adaptation strategies for future generations," Cuthbert said.