Groundwater is the largest accessible freshwater resource worldwide and is of critical importance for irrigation, and so for global food security. For many regions of the world where groundwater abstraction exceeds groundwater recharge, persistent groundwater depletion occurs. A direct consequence of depletion is falling groundwater levels, reducing baseflows to rivers and harming ecosystems. Also, pumping costs increase, wells dry up and land subsidence can occur.
Water demands are expected to increase further due to growing population, economic development and climate change, posing the urgent question how sustainable current water abstractions are worldwide and where and when these abstractions approach conceivable limits with all the associated problems.
Here, we estimated past and future trends (1960-2050) in groundwater levels resulting from changes in abstractions and climate and predicted when limits of groundwater consumption are reached. We explored these limits by predicting where and when groundwater levels drop that low that groundwater becomes unattainable for abstractions and how river flows are affected.
Water availabilities, abstractions, and lateral groundwater flows are simulated (5 arcmin. resolution) using a coupled version of the global hydrological model PCR-GLOBWB and a groundwater model based on MODFLOW. The groundwater model includes a parameterization of the worlds confined and unconfined aquifer systems, needed for a realistic simulation of groundwater head dynamics.
Results show that, next to the existing regions experiencing groundwater depletion (like India, Pakistan, Central Valley) new regions will develop, e.g. Southern Europe, the Middle East, and Africa. Using a limit that reflects present-day feasibility of groundwater abstraction, we estimate that in 2050 groundwater becomes unattainable for ~20% of the global population, mainly in the developing countries and pumping cost will increase significantly.
Largest impacts are found during times with low flows for intensively irrigated regions. Regionally an increase or decrease in exploitation cost, caused by falling or rising groundwater levels, will be an essential factor in future economic development and should be considered to warrant a reliable groundwater supply under changing climate conditions.
(Authors: Ludovicus P. Van Beek, Inge de Graaf, Edwin Sutanudjaja, Yoshihide Wada, Mark FP Bierkens, “Limits to global groundwater consumption”. AGU Fall Meeting, San Francisco, 15/XII/2016)