Abstract
Rivalry in extractive CPR, like groundwater, implies that agents extract as much as they need, and even more if they fear that others behave the same way (Gardner et al., 1990; Walker et al., 1990 and 2000), leading to the ‘tragedy of the commons’ (Hardin, 1968). Users depleting a groundwater CPR typically face two types of appropriation externalities (Gardner et al., 1997): a static externality, whereby individuals’ extraction costs at any given date are affected by the total level of extraction at that date, and a dynamic externality, whereby the extraction cost any later date is affected by past cumulative extractions.
Groundwater is a very important source of irrigation water, the latter representing more than 70% of the total water uses on earth (FAO, 2022). In North Africa half of the current groundwater water withdrawals exceed natural rates of water recharge (Mayaux et al., 2022). Maghreb Countries are highly dependent on their groundwater resources for their agricultural development. The public policies of the last decades triggered radical changes in newly irrigated areas (extension areas) and in traditional oases (Kadiri et al., 2022). This resulted in a quick intensification of local agriculture, like in Tunisia, where oases are currently facing sustainability concerns due to “uncontrolled expansion of irrigated areas, overexploitation of groundwater resources, and soil degradation” (Ghazouani et al., 2009; Mekki et al., 2013).
In Tunisia, the Complex terminal aquifer in Kebili is under the threat of overexploitation, as its exploitation leads to a 1 metre lowering of the water table/year. This is due to the combination of a very low level of water recharge and high level of water use for irrigation mainly (Trigui et al., 2021).
In Tunisian oases, traditional farmers are organised in water users associations, called GDA (French acronym for Agricultural Development Groups), which coexist with newly settled extension farmers. Many GDA farmers also have plots in the extensions, where, like the extension farmers, they dig illicit private boreholes that are not declared to the local authority for water management (CRDA) (Farolfi et al., 2022).
Unregulated water extraction in the extensions is a major cause for groundwater overexploitation (Mekki et al., 2013), a situation that is likely to lead to the collapse of the system in the short or medium term. Urgent and drastic policy measures are therefore needed (Petit et al., 2017) to prevent such adverse outcome.
Current policies to match the problem are limited to the attempt by the CRDA to reduce access to water by limiting the number of boreholes. However, the overwhelming presence of illicit boreholes in Tunisian newly irrigated areas shows clearly the ineffectiveness of the measure. Alternative governance tools are necessary in order to face groundwater overexploitation in the Tunisian oases.
We address the issue of designing appropriate policy instruments to prevent overexploitation, based on laboratory experiments and lab-in-the-field experiments. Our aim is to compare several feasible instruments that can potentially be implemented in the field, by adopting a step-by-step experimental approach. We target particularly informational instruments (Tews et al., 2003) due to their lower cost compared to the complex administration often needed in order for command-and-control regulation to work properly or to implement and enforce economic instruments. We also observe the role of communication among CPR users to reduce overexploitation. In a first step, we will try to establish the effectiveness of the aforementioned alternative instruments to address the issue of overexploitation in a framed laboratory setting. This is done with standard student subjects, using the Montpellier Laboratory of Experimental Economics (LEEM) facility. In a second step, we replicate the standard laboratory experiments with Tunisian students of the National Institute for Agricultural Research in Tunis (INAT). The final step will be to replicate the lab experiment with Tunisian farmers directly involved in the exploitation of groundwater in the oasis of Jemna in Kebili region, in a lab-in-the-field setting. Step 1 will allow us to provide causal evidence of the effectiveness of the instruments and internal validity. Step 2 will allow us to control for the nationality of the student subjects and the robustness of the lab-findings according to location (Montpellier vs Tunis). The final step will provide external validity of the experimental findings of steps 1 and 2, following the methodology of Bchir (2014).
To this end, like Gardner et al. (1997), we designed laboratory experiments to assess the performance of various groundwater governance policies and the applicability of game theory to behaviour in such a system. We use the groundwater extraction dynamic model by Gardner et al. (1997) to run experiments in the lab (France and Tunisia) and in the field, with Jemna oasis farmers, in order to test the performance of various groundwater governance policies in the studied frame. The model implies a CPR recharge rate = 0, which is adapted to the local situation, as indicated by Trigui et al. (2021).
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