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Groundwater represents the largest source of fresh water on the planet. So far it has not been greatly affected by climate change, but that may change in the coming decades, a team of researchers found.
Groundwater systems are expected to take much longer to respond to climate change than surface waters, which means that in many parts of the world the marked changes brought about by climate change could take up to a century.
So you shouldn't worry because at least the future is foreseeable?
Not so, says another team of scientists. Groundwater is the largest source of water in agriculture and their results show that almost a fifth of the catchment areas where groundwater is pumped for irrigation suffer from flows so low in streams and rivers that their freshwater ecosystems are feeling the worst part.
"Already, unsustainable pumping of groundwater exceeds recharge from rainfall and rivers, leading to substantial drops in groundwater levels and losses of groundwater from storage, especially in heavily irrigated regions," write the scientists in a new study published in the journal Nature.
The study analyzed groundwater sources and rivers as globally interconnected systems with the aim of showing the effects of global groundwater withdrawal on surface water levels.
"When groundwater levels drop, groundwater discharges to streams decrease, recede, or even stop altogether, thus slowing stream flow, with potentially devastating effects on aquatic ecosystems," the scientists explain. .
And there is worse news: by mid-century, half of the groundwater sources will likely be affected.
"The effects can already be seen in the Midwest of the United States and in the Indus Valley project between Afghanistan and Pakistan," says Inge de Graaf, a hydrologist at the University's Institute of Earth and Environmental Sciences. from Freiburg who led the study. .
“If we continue to pump as much groundwater in the coming decades as we have done so far, a critical point will also be reached for the southern and central European regions, such as Portugal, Spain and Italy, as well as in the North African countries. De Graaf warns.
According to their estimates, anywhere between 42% and 79% of the regions where groundwater is drawn will have reached its limits by 2050. “Climate change may even accelerate this process, as we expect less precipitation, which will increase even more the extraction of groundwater and it will cause dryness and in some places this will be completely, ”adds de Graaf.
Over the past half century, rising temperatures and increasing human populations have seen the demand for groundwater rise at an accelerating rate globally. Many sources of groundwater are depleted faster than they can be replenished through rainwater. Scientists say they have found alarming how sensitive freshwater ecosystems are to even relatively small drops in groundwater levels.
And things may get worse in the coming decades as climate change accelerates and our dependence on groundwater sources grows.