Groundwater Warming Poses a Significant Challenge in an Age Increasingly Impacted by Climate Cha

As the largest unfrozen freshwater resource on Earth, groundwater is vital for sustaining life. Researchers at the Karlsruhe Institute of Technology (KIT) have delved into how global warming affects groundwater temperatures and the implications for humanity and the environment. Their findings, published in Nature Geoscience, reveal a concerning future where groundwater temperatures could exceed safe drinking levels for millions of people.

Groundwater, stored in underground formations of soil, sand, and rock called aquifers, is crucial for drinking water and agriculture. Over 50% of the U.S. population relies on groundwater, with nearly all rural residents depending on it. Aquifers, made of materials like gravel, sand, and limestone, allow water to flow through due to their permeability. The water table, which varies in depth, rises with rain and snowmelt but can fall with heavy groundwater use.

The KIT study highlights the significant impact of climate change on groundwater. "To close this gap, we have simulated the projected changes in global groundwater temperatures through 2100," said Dr. Susanne Benz from the Institute of Photogrammetry and Remote Sensing at KIT, which prepared the study in cooperation with Dr. Kathrin Menberg and Professor Philipp Blum from the Institute of Applied Geosciences at KIT. "We can provide maps showing global groundwater temperatures at various depths beneath Earth's surface. 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."

Using SSP 2-4.5 and SSP 5-8.5 climate scenarios, which reflect different socioeconomic pathways and greenhouse gas trends, the researchers found alarming results. By 2100, groundwater temperatures could rise by 2.1°C under SSP 2-4.5 and by 3.5°C under SSP 5-8.5. Currently, about 30 million people live in regions where groundwater exceeds safe drinking temperatures. This number could soar to between 77 million and 588 million people by 2100, depending on climate and population trends.

The effects of warmer groundwater extend beyond drinking water safety. 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 said.

Moreover, increased groundwater temperatures can exceed critical thresholds in water distribution networks, promoting the growth of pathogens like Legionella spp. Fish species, particularly salmon, could face reproductive challenges as groundwater-dependent spawning grounds warm.