A new paper published on 21 January in Nature Climate Change has provided some insights into potential changes in important groundwater reserves as a result of climate change (1). The researchers highlight the potentially lengthy response times that can vary between arid and humid regions.
Groundwater is the world’s largest source of freshwater and is found underground in cracks and spaces within soil, sand, and rocks. The water typically flows slowly through rocks and soil but is often a critical source of irrigation for growing crops, an important component in many industrial processes, and a source of recharge for lakes, rivers, and wetlands. In addition, more than two billion people rely on groundwater as their source of freshwater. However, less rainfall owing to climate change can lead to fluctuation of water levels in the ground.
Despite the important role of groundwater, the influence of climate change on groundwater systems is not well understood. As the authors note, most models of the global climate, the Earth system, and land surface exclude groundwater. To rectify this, the international team led by researchers from Cardiff University combined the results of a global-scale groundwater model with hydrological data sets ― data on the movement of ground and surface water ― to estimate how long climate will take to affect groundwater and to identify locations particularly sensitive to those changes.
Groundwater is typically replenished through rainfall― via the so-called recharge process ― but takes a lot longer to respond to climate change than surface water. The authors found that it could take 100 years for more than half of the world’s groundwater systems to completely respond to changes that are happening right now in the environment. They also found that important areas of groundwater discharge in naturally humid regions are likely to be more responsive to fluctuations in the global climate compared to arid regions, which respond on much longer timescales.
The authors point to potential ‘hidden’ impacts on the water flows needed to sustain streams and wetlands in dry areas, which could threaten water sources required for important domestic, agricultural, and industrial uses. Therefore, future assessments of the impact of climate change on hydrological drought require estimates of ‘groundwater responsiveness.’
According to the authors, the new analysis “provides a new framework for understanding global water availability changes under climate change.” These new findings could “improve the decision-making process with regard to adaptation strategies to changing drought frequencies under climate change.” However, the authors suggest that appropriately long timescale will need to be incorporated into water resource decision making.
Furthermore, lags in groundwater hydrology should be considered in strategies that rely on groundwater instead of surface water. This lag in the response of baseflow to rivers and wetlands is significant; therefore, new approaches will be needed to prevent water shortages, particularly in areas where surface water supplies are less available.
(1) Cuthbert, M.O. et al. Global patterns and dynamics of climate–groundwater interactions. Nature Climate Change (2019). DOI: 10.1038/s41558-018-0386-4