Optimal groundwater pumping strategies that include surface water

Scientists from Utrecht University derived analytical solutions for economically optimal groundwater pumping strategies that also account for the interaction between groundwater and surface water; a feature of natural groundwater systems previously omitted in analytical treatments.

Over the last few decades, increasing population and economic development have caused a steep rise in the demand for food and water. To meet these increasing demands, irrigated agriculture has become increasingly dependent on groundwater. This, in turn, has led to the overexploitation of groundwater resources in many parts of the world and the persistent increase in groundwater depth.

The problem with lowering water tables is that the costs of extracting groundwater increase up to a point that these costs surpass the revenues from crop production, thus leading to economic depletion of the aquifer (aquifer -> groundwater bearing layer). Already from the 1960s on, economists have developed theories that prescribe how groundwater pumping rates should develop over time to maximize total profits till economic depletion. This optimal control depletion requires that all the farmers that pump water from the aquifer fully cooperate or obey some groundwater authority. However, for many large aquifers it turns out that profits from this so-called controlled depletion are not much larger than when all farmers are selfish and compete for the same groundwater. This result is called the Gisser-Sánchez effect and entails that groundwater management is pointless.

These classical theories, however, neglect the fact that groundwater often interacts with rivers and streams and that part of the groundwater that is pumped leads to a decline in streamflow. A team of hydrologists led by Marc Bierkens therefore extended the classical economic theory of controlled depletion with groundwater-surface water interaction. Their extended hydroeconomic model also includes so called environmental externalities. These are the hidden costs of harming the environment, such a decreased streamflow or desiccating wetlands, that result from the pumping of groundwater. The scientists applied their model to all the major groundwater irrigation areas of the world. Results show that for most of these areas controlled depletion of groundwater yields higher economic benefits than selfish competition, provided that the costs to the environment are taken into account.

Article

Bierkens, M.F.P., van Beek, L.P.H. & Wanders, N. (2024). 'Gisser-Sánchez revisited: A model of optimal groundwater withdrawal under irrigation including surface–groundwater interaction', Journal of Hydrology, 635, 131145, 1-22, https://doi.org/10.1016/j.jhydrol.2024.131145