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Global Warming Could Make Groundwater Undrinkable for Future Generations

In a recently published study in the journal Nature Geoscience, researchers from the Karlsruhe Institute of Technology examined the implications of rising global temperatures for the environment and human population. According to their analysis, by 2100, more than 75 million people will likely live in regions where groundwater temperatures exceed the highest acceptable level for drinking water, more than in any other country.

Global Warming Could Make Groundwater Undrinkable for Future Generations
Recently published KIT research shows that overly warm groundwater could affect millions of people by 2100. Image Credit: Susanne Benz, Karlsruhe Institute of Technology

Earth’s climate system is heating up due to the increased concentration of greenhouse gases in the atmosphere, which limits the amount of heat that can escape. The oceans absorb a significant portion of this heat, although groundwater and soil also serve as heat sinks. However, not much is now understood about how groundwater is affected by surface warming in both space and time.

To close this gap, we have simulated the projected changes in global groundwater temperatures through 2100. We can provide maps showing global groundwater temperatures at various depths beneath the 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.

Dr. Susanne Benz, Institute of Photogrammetry and Remote Sensing, Karlsruhe Institute of Technology

Dr. Susanne Benz prepared the study in cooperation with Dr. Kathrin Menberg and Professor Philipp Blum from the Institute of Applied Geosciences at KIT.

The researchers' predictions were based on the SSP 2-4.5 and SSP 5-8.5 climatic scenarios. These scenarios show several paths for socioeconomic development and variations in the concentration of greenhouse gases in the atmosphere.

Regarding potential future trends in greenhouse gas concentrations, SSP 2-4.5 falls in the medium range, whereas SSP 5-8.5 represents the upper extreme.

Millions of People Affected by Overly Warm Drinking Water

According to the study, in the SSP 2-4.5 scenario, groundwater temperatures will rise by 2.1 ºC by 2100, and in the SSP 5-8.5 scenario, they will increase by 3.5 ºC.

There are already about 30 million people living in regions where the groundwater is warmer than stipulated in the strictest drinking water guidelines. 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.

Dr. Susanne Benz, Institute of Photogrammetry and Remote Sensing, Karlsruhe Institute of Technology

The study estimates that for SSP 2–4.5, the number would be 77–188 million individuals, and for SSP 5–8.5, it would be 59–588 million. The wide variances can be attributed to both population trends and geographical variations in climate change.

The Andes and the Rocky Mountains are examples of mountainous places with deep water tables where the researchers predicted the lowest warming rates.

Temperature Changes Affect Ecosystems

The temperature of groundwater affects several chemical, biological, and physical processes that are important for water quality.

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.

Dr. Susanne Benz, Institute of Photogrammetry and Remote Sensing, Karlsruhe Institute of Technology

According to Benz, warmer groundwater also impacts aquatic biogeochemical processes, geothermal energy potential, temperature regimes in rivers, and ecosystems that depend on groundwater. It may also be hazardous to the carbon and nutrient cycles and challenge biodiversity.

Increased temperatures in groundwater and near-surface areas can also lead to the overflow of key thresholds in water delivery networks. This may impact human health, for example, by encouraging the spread of infections like Legionella spp. The shifting environmental factors particularly impact salmon and other fish species.

Their reproduction could be endangered if groundwater-dependent spawning grounds in rivers become too warm. 

Benz said, “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.”

Journal Reference:

Benz, S. A., et al. (2024). Global groundwater warming due to climate change. Nature Geoscience.

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