Carried out by scientists in Germany, this is the first global groundwater study to use the new representative concentration pathways scenarios from RCP2.6 (low concentrations) to RCP8.5 (high concentrations) combined with five different climate models. The researchers found that the majority of the world's population would not see a significant change in renewable groundwater resources under scenario RCP2.6. However, more than 70% of the world's population would experience a greater than 10% change in groundwater recharge under scenario RCP8.5.

But the researchers, from the Goethe University Frankfurt and the University of Kassel, point out that, while they have come to some important conclusions about future global groundwater recharge, they also found that there was a surprising level of variation between the climate-model predictions.

"It is important that, when looking at our results, researchers don't just look at the mean data, but at the results from each individual model," said Felix Portmann. "We were surprised to see that the models only agree on around one third of the area of the globe. In all other areas of the globe there are large variations. For example, in northern India, where groundwater resources are highly stressed, depending on the chosen climate model, a range from a strong reduction, no change, to strong increases can be expected."

Despite these large variations, the study clearly shows that climate change will have a lasting effect on groundwater recharge, and so impact renewable groundwater resources worldwide. Groundwater is currently the source of around 35% of global human water withdrawals; due to increased temporal variability of surface-water flows, climate change is likely to lead to higher demands for groundwater.

"Our research shows that populations around the world will be affected by changes in renewable groundwater resources under three of the four scenarios we modelled," said Portmann. "It is important that the research community comes up with accurate and reliable projections so that regions can prepare for changes in renewable groundwater resources, irrespective of whether the projected change results in an increase or a decrease."

Portmann also points out that the spatial patterns differ from model to model and also to those of a previous study. "But the uncertainty from climate-model projections does not prevent us from clearly identifying benefits of emissions reductions," he said. "For each degree of global mean temperature rise, an additional 4% of the global land area is affected by a decrease in groundwater recharge of more than 30%. This shows that emissions reduction is important."

The team published the study in Environmental Research Letters (ERL).

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