Climate Change: Rising Temperatures Affect Groundwater Quality

KIT researchers are investigating the effects of climate change on groundwater resources and the associated consequences

Groundwater is the largest unfrozen freshwater reservoir in the world and is crucial for life on Earth. Researchers at the Karlsruhe Institute of Technology (KIT) have now investigated how global warming affects its temperature and what this means for humans and nature. The study shows that by the year 2100, more than 75 million people are expected to live in areas where groundwater exceeds the highest limit for drinking water temperature set by a country. Their results have been published in Nature Geoscience. (DOI: 10.1038/s41561-024-01453-x)

The climate system is warming. The reason for this is the increased concentration of greenhouse gases in the atmosphere, which limit heat radiation. The oceans absorb a large part of this heat, but soils and groundwater also act as heat sinks. However, little is known so far about how this warming of the earth's surface affects groundwater spatially and temporally. "To close the gap, we have presented the predicted changes in groundwater temperature up to the year 2100 on a global level," says Dr. Susanne Benz from the KIT Institute of Photogrammetry and Remote Sensing (IPF), who prepared the study together with Dr. Kathrin Menberg and Professor Philipp Blum from the KIT Institute of Applied Geosciences (AGW). "We provide global temperature maps for groundwater at different depths below the earth's surface. These show that the highest groundwater warming rates are to be expected in places with a shallow groundwater table and/or high atmospheric warming worldwide."

The researchers refer to the climate scenarios "SSP2-4.5" and "SSP5-8.5". Such scenarios describe various socio-economic developments as well as different trends in atmospheric greenhouse gas levels in the future. SSP2-4.5 represents roughly the middle of possible future greenhouse gas developments, SSP5-8.5 the upper end.

Millions of people affected by drinking water that is too warm
The study shows that groundwater temperatures will rise by 2.1 degrees Celsius according to SSP2-4.5 and by 3.5 degrees Celsius according to SSP5-8.5 by the year 2100. "Around 30 million people already live in areas where the groundwater is warmer than the strictest guidelines for drinking water stipulate. This means that the water there cannot be safely drunk directly; it must be boiled, for example. This is because the drinking water in the water pipes is also heated up by the heat in the ground," says the scientist. "Depending on the climate scenario, up to several hundred million people will be affected by the year 2100." According to SSP2-4.5, the number will rise to 77 to 188 million people, and according to SSP5-8.5 to 59 to 588 million, according to the study. The strong fluctuations are related to the spatial variability of climate change and population development. The researchers predict the lowest warming rates for mountainous regions with low groundwater levels, such as the Andes or the Rocky Mountains.

Temperature changes affect ecosystems
The temperature of groundwater plays a crucial role in water quality. It influences a variety of chemical, biological and physical processes. "If the conditions are right, rising groundwater temperatures can indirectly lead to the accumulation of harmful substances such as arsenic or manganese in groundwater. These increased concentrations can have a negative impact on human health, especially if groundwater is used as a source of drinking water," says Benz. In addition, warmer groundwater affects the temperature balance of rivers, groundwater-dependent ecosystems, aquatic biogeochemical processes and geothermal potential. This poses a challenge for biodiversity and carries the risk of disrupting carbon and nutrient cycles.

In addition, the increased temperatures in the near-surface soil and groundwater can exceed critical thresholds in the water distribution networks. This could have health consequences, for example through the growth of pathogens such as Legionella spp. Fish species, especially salmon, are also affected by the changed conditions. Spawning grounds in rivers that depend on groundwater could become too warm due to warming, thus endangering reproduction. "Our results show how important it is to take measures to protect groundwater resources and to find sustainable solutions to counteract the negative effects of climate change on groundwater," Benz appeals.

Details about the KIT Climate and Environment Center
As “The Research University in the Helmholtz Association”, KIT creates and imparts knowledge for society and the environment. The aim is to make significant contributions to global challenges in the fields of energy, mobility, and information. To this end, around 10,000 employees work together on a broad disciplinary basis in natural sciences, engineering, economics, and humanities and social sciences. KIT prepares its 22,800 students for responsible tasks in society, business, and science through research-oriented university studies. KIT's innovation activities build a bridge between knowledge and application for social benefit, economic prosperity, and the preservation of our natural resources. KIT is one of Germany's universities of excellence.