New Delhi: Under a medium emissions scenario, groundwater at the depth of Water Table excluding Permafrost Regions is likely to warm by an average of 2.1°C by the end of 21st Century, a recent study carried out on a global scale revealed.

However, the warming patterns of shallow groundwater in various regions substantially differ and are influenced by the spatial variability in climate change effects and the depth of water table, a panel of researchers clarified in the journal ‘Nature Communications’.

Aquifers house the most substantial reserve of unfrozen freshwater, playing a pivotal role in supporting life on our planet. Nevertheless, a little has been understood so far about the intricate ways in which groundwater reacts to surface warming across various spatial and temporal dimensions.

The researchers simulated current and projected groundwater temperatures, focusing on diffusive heat transport. It was demonstrated that higher groundwater temperatures impact geothermal potential, groundwater-dependent ecosystems, stream thermal regimes, aquatic biogeochemical processes, and groundwater quality.

Surprisingly, the projections showed that around 77 million to 188 million people will live in areas where groundwater temperatures exceed the highest drinking water thresholds set by any country.

“Warming of entire climate system of Planet Earth is a consequence of the radiative imbalance resulting from increased concentrations of greenhouse gases,” explained a member of the panel Dylan J. Irvine from Charles Darwin University, Australia.

While oceans take in the majority of this additional heat, the terrestrial subsurface and groundwater also absorb significant amounts. Under stable climate conditions, seasonal temperature fluctuations extend to a depth of 10–20 meters, beyond which temperatures typically rise with depth following the geothermal gradient.

Subsurface temperatures within the shallow crust are predominantly regulated by one-dimensional (1D) (vertical) diffusive heat transport. Although water flow-induced heat advection can contribute, its impact is typically minor and sometimes negligible in determining subsurface temperatures.

This is especially evident at larger spatial scales, where the impacts of groundwater movement through faults and fractures, along with interactions with surface water sources, typically become smoothed out or averaged.

“Our analyses are grounded in rational hydraulic and thermal assumptions, resulting in the conservative estimates that facilitate both the reconstruction of past groundwater temperatures and the prediction of future trends,” Dylan J. Irvine further said.