JRC explains | 16 January 2025 | Joint Research Centre
Mountains are more than familiar features of the landscape—they have long inspired humans with their beauty and dramatic presence. Yet beyond their cultural significance, mountains play a far more practical role: they act as nature’s water towers, storing and releasing water that sustains billions of people and countless ecosystems downstream. As the climate warms, how will this critical role be affected?
How do mountains store and release water?
Mountains receive significant precipitation, storing large amounts of high-quality water in lakes, reservoirs, and snow caps. The stored water is slowly released through natural processes like snow melt or via springs, becoming especially important during dry periods.
When temperatures go up and precipitation becomes less frequent, this stored water helps sustain rivers, ecological habitats, and human activities downstream. However, climate change is altering water availability across the world and making this release of water from mountains less reliable.
“Hidden” water
While surface water storage in lakes and snow caps is well understood, recent research highlights the overlooked importance of water “hidden” inside a mountain and stored in aquifers or underground reservoirs.
Recent field studies have revealed that fractured rock formations, even those with low permeability, can host substantial volumes of water during wet periods. This finding challenges the earlier assumption that water flows and storage are largely confined to near-surface areas and play a minimal role in the hydrological cycle.
But what can be the role of such hidden processes in a world that is becoming hotter and drier?
The role of the JRC
A new joint study by the Joint Research Centre (JRC) and the University of Trento sheds light on how a hotter, drier climate could disrupt the ability of mountains to store and release water.
The study, recently published on the open access journal “Water Resource Research”, specifically focuses on the role of subsurface water flows in mountain environments. The goal was to understand how mountains’ characteristics — such as size, subsurface permeability, and rainfall patterns — affect important aspects of the hydrological cycle and the amount and quality of water that a mountain can store.
What are the ideal conditions for underground water storage?
The JRC study highlights the amount of time water spends in the subsurface as a critical aspect, as it affects the water’s dilution, mixing from various sources, its chemical and microbial reactions, redox conditions, and contaminant transport and distribution. And while longer travel times are not always better for water quality, they are necessary to achieve large volumes of water in underground storage.
The volume of water stored underground is also important to evaluate the resilience of the water cycle during droughts, as a larger volume would allow for better maintenance of rivers and ecosystems downstream.
According to the same study, how rainfall water splits between flows on the surface and flows in deep rocks has a direct effect on how the landscape responds to the rainfall, with the distribution of rainwater between the surface and the underground influencing flood risks or water storage capacity.
Finally, the study highlights the permanently active river network’s critical role in evaluating where rivers and streams have enough flowing water to support habitats and ecosystems.
What happens next?
By acting as natural water towers, mountains could offer a buffer against droughts, sustain ecosystems, and provide freshwater for billions downstream. These new insights could help answer the question on whether the water resources found inside mountains can be useful in a world that is becoming more and more unpredictable in terms of climate.
Research by JRC scientists is helping us understand the hidden dynamics of subsurface water flows and identify the regions where water availability is more sensitive and vulnerable to climate change. The study’s results could also help equip policymakers and communities with the knowledge to better manage this hidden water and to improve predictive modelling for environmental and climate systems.
For further details, please visit the article on AGU website: Morphological and Hydrogeological Controls of Groundwater Flows and Water Age Distribution in Mountain Aquifers and Streams