Researchers at the Karlsruhe Institute of Technology (KIT) have investigated how global warming is affecting groundwater quality and what it means for humanity and the environment.
As the world’s largest unfrozen freshwater resource, groundwater is crucial for life on Earth.
However, the study indicates that by 2100, more than 75 million people are likely to be living in regions where the groundwater temperature exceeds the highest threshold set for drinking water by any country.
The full set of results is published in Nature Geoscience.
Climate change is heating the Earth, including water
Earth’s climate system is heating up due to the atmosphere’s increased concentration of greenhouse gases, which limits the amount of heat that can be radiated away.
The oceans absorb a substantial fraction of this heat, but soil and groundwater also act as heat sinks. However, little is known thus far about the effects Earth’s surface warming has on groundwater quality over space and time.
“We can provide maps showing global groundwater temperatures at various depths beneath Earth’s surface,” explained Dr Susanne Benz from the Institute of Photogrammetry and Remote Sensing at KIT.
“The maps show that the world’s highest groundwater warming rates can be expected at locations with a shallow groundwater table and/or high atmospheric warming.”
The researchers based their projections on the SSP 2–4.5 and SSP 5–8.5 climate scenarios. These scenarios reflect different socioeconomic development pathways and different trends in the concentration of atmospheric greenhouse gases in the future.
Millions of people affected by depleting groundwater quality
The study indicates that by 2100, groundwater temperatures will rise by 2.1°C in the SSP 2–4.5 scenario and by 3.5°C in the SSP 5–8.5 scenario.
“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.”
Depending on the scenario, as many as several hundred million people could be affected by 2100.
According to the study, the figure would be 77 to 188 million people for SSP 2–4.5 and 59 to 588 million for SSP 5–8.5.
How temperature changes affect ecosystems
Groundwater temperature plays a crucial role in water quality, influencing several chemical, biological, and physical processes.
Benz said: “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.”
A further effect of increased near-surface and groundwater temperatures is that critical thresholds can be exceeded in water distribution networks.
This could have human health implications, such as pathogen growth.
Fish species, especially salmon, are also affected by the changing conditions. Their reproduction could be endangered if groundwater-dependent spawning grounds in rivers become too warm.
“Our results show how important it is to take action to protect groundwater quality and find lasting solutions to counteract the negative impact of climate change,” Benz concluded.
