Groundwater, the largest source of fresh water in the world from which 2 billion people rely on, will take a long time to respond to climate change and the future generation will suffer from it.

In a new study, a team of researchers described groundwater as an environmental "time bomb" as climate-related changes in rainfall disrupt the process of "recharge." They warned that nearly half of the aquifers around the world are projected to be depleted within a century.

The findings were published in the journal Nature Climate Change on Monday, Jan. 21.

A Ticking Time Bomb

Groundwater is found in the cracks and space in soil, sand, and rock. It is replenished slowly through rainfall, a process known as recharge, and discharges water into lakes, rivers, and oceans to maintain an overall balance.

However, because of climate change, the recharge process is being disrupted. The lack of rainfall, for example, is causing the level of groundwater to drop until the balance is once again restored.

The long-term impacts of climate change on the replenishment cycle of groundwater and when it will begin to manifest still remain a question. For the study, the first to investigate the issue, the team used groundwater model results in combination with hydrologic datasets to estimate a timescale in which the groundwater system will respond to climate change.

They found that the groundwater in humid areas like the Florida Everglades is likely to respond to climate change in a much shorter timescale. However, in more arid regions like the Sahara Desert, groundwater would have a much longer response time. The researchers estimate that it could take over 100 years for groundwater systems to fully respond to the changing climate.

"This means that in many parts of the world, changes in groundwater flows due to climate change could have a very long legacy," explained Mark Cuthbert of Cardiff University's School of Earth and Ocean Sciences and the lead author of the study. " This could be described as an environmental time bomb because any climate change impacts on recharge occurring now, will only fully impact the baseflow to rivers and wetlands a long time later."

Call To Action

The team called groundwater as one of the hidden impacts of climate change. The heating planet is bringing extreme weather events such as longer droughts and bigger superstorms, disrupting the groundwater systems around the world. They are calling for immediate action to make sure that the future generations will enjoy the same privilege of having accessible freshwater that the present global population has now.

Cuthbert added that in the future, some parts of the world might get "wetter" and some might get "drier" due to climate change. The intensity of rainfall is "very significant for groundwater."  

"Groundwater is out of sight and out of mind, this massive hidden resource that people don't think about much yet it underpins global food production," he stated.