The Multi‐Scale Dynamics of Groundwater Depletion

Abstract

The depletion of groundwater resources is a widespread phenomenon that can jeopardize both water and food security by making groundwater less accessible, degrading water quality, reducing surface water flow, and compromising the buffering capacity provided by groundwater reserves (Aeschbach-Hertig & Gleeson, 2012). There is abundant documentation of the severity and extent of groundwater depletion, especially in intensively cultivated areas (Bierkens & Wada, 2019;Gleeson et al., 2012). However, undesirable depletion occurs despite knowledge of the problem among water users and despite evidence that effective management and cooperation can reduce the adverse effects of exploitation (Madani & Dinar, 2012b;Ostrom, 1990).Here we address some basic questions about the physical and economic aspects of long-term groundwater depletion. What controls pumping decisions in an unconfined aquifer with multiple wells operated by different users? Can cooperation among the aquifer users increase the benefits and reduce the adverse impacts of pumping? What are the revenue and environmental implications of well yield limitations and regulatory constraints? How are the effects of pumping distributed between storage depletion and reductions in aquifer outflow? These research questions address groundwater depletion issues that are long-standing but have largely remained unresolved, at least in any quantitative sense. Quantitative answers to these questions can provide useful insight about how depletion occurs and how it might be reduced.In order to address our research questions, we need to consider the economically driven pumping decisions made by the agents who use the aquifer (e.g., farmers or irrigation districts) as well as physical processes and policies that may constrain these decisions. One way to include decision-making is to treat pumping rates as time-dependent variables (rather than inputs) that agents continually adjust to maximize particular objectives. This perspective naturally leads to an optimal control formulation of the decision problem. Solutions to this problem describe the pumping and storage histories that can be expected for particular aquifers and management strategies. The optimization process is constrained by physical groundwater flow constraints and by well yield and regulatory constraints that may limit pumping.The constraints required in this decision-driven approach to depletion analysis need to consider local conditions at the well scale, which guide pumping decisions, as well as conditions at larger aquifer scales where the economic and environmental impacts of agent decisions are felt. Consequently, the relevant spatial scales for our

Hydro Economic Asymmetries and Common‐Pool Overdraft in Transboundary Aquifers

“…A discount rate can be incorporated to determine the sequence at which the total volume is extracted during the period, but accounting for its effect on strategic behavior would require a dynamic game where each player must make a sequence of multiple decisions along an explicit timeline. For example, Sahu and McLaughlin (2021) compares the effect of dynamic pumping decisions with and without foresight (i.e., infinite vs. finite) on the depletion of shared aquifers. A similar approach can be used to investigate economic and hydro‐geologic asymmetries in dynamic groundwater pumping games but, again, analytical tractability is likely to remain a major challenge.…”

“…Because formal markets for water are rare, α i is often a shadow price to be determined using proxies, such as the cost of conveyance infrastructure (Müller et al., 2017), or the cost of obtaining water from an alternative source (Penny, Müller‐Itten, et al., 2021). The linear form of the utility function implies that (a) the cost of drilling and setting up the pumps is small compared to the life‐time (energy) costs of operating them, (b) the shadow price of water is exogenously given and not itself affected by groundwater production (see Dang et al., 2016), (c) systemic costs of decreased water levels beyond pumping cost externalities (e.g., decreased streamflow production (Sahu & McLaughlin, 2021)) are neglected and (d) water is the limiting factor of production. This last assumption can be relaxed by adding a pumping threshold to utility function beyond which pumping does not generate additional benefits (Penny, Müller‐Itten, et al., 2021).…”