By 2100, more than 75 million people are likely to be living in places where the groundwater is too hot to drink, according to a new study. Groundwater temperatures are forecast to rise by up to 3.5°C (6.3°F) by the end of the century, which would mean they exceed the highest threshold set for drinking water by any country.
Groundwater is crucial for life on Earth, and yet relatively little is known about how it responds to climate change over space and time. What we do know is that as things get hotter, it will act as a heat sink, absorbing excess heat caused by global warming.
To work out what this might look like, researchers at the Karlsruhe Institute of Technology (KIT) have modeled projected changes in global groundwater temperatures through to 2100. Basing their projections on two climate scenarios, SSP 2–4.5 and SSP 5–8.5, which reflect different socioeconomic development pathways and future greenhouse gas concentrations, they have determined that groundwater temperatures will rise by 2.1°C (3.8°F) or 3.5°C (6.3°F), depending on the scenario.
Some parts of the world will feel this spike more acutely, explained study author Dr Susanne Benz, from the Institute of Photogrammetry and Remote Sensing at KIT, in a statement: “[T]he world’s highest groundwater warming rates can be expected at locations with a shallow groundwater table and/or high atmospheric warming.”
What this means, is that for millions of people worldwide, groundwater will become undrinkable.
“There are already about 30 million people living in regions where the groundwater is warmer than stipulated in the strictest drinking water guidelines,” said Benz. “That means it may not be safe to drink the water there without treatment. It may need to be boiled first, for example. The drinking water also gets warmed up in water pipes by heat in the ground. Depending on the scenario, as many as several hundred million people could be affected by 2100.”
In fact, the research suggests that in the next 76 years, between 77 to 188 million people could be affected as per SSP 2–4.5, and 59 to 588 million under SSP 5–8.5.
In case you’re wondering what’s wrong with a little warm water, let us explain. Groundwater’s temperature influences a suite of biogeochemical processes that in turn impact its quality. For example, “under certain conditions, rising groundwater temperatures can lead to increasing concentrations of harmful substances like arsenic or manganese. These higher concentrations can have a negative impact on human health, especially when groundwater is used as drinking water,” Benz explained.
It can also facilitate the growth of pathogens such as Legionella spp, and affects ecosystems, biodiversity, and carbon and nutrient cycles. All in all, it’s not great news for us or the other organisms that rely on groundwater systems.
“Our results show how important it is to take action to protect groundwater and find lasting solutions to counteract the negative impact of climate change on groundwater,” Benz concluded.
The study is published in Nature Geoscience.
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