Private Exploitation of the North-Western Sahara Aquifer SystemJournal articleAmine Chekireb, Julio Goncalves, Hubert Stahn et Agnès Tomini, Environmental Modeling & Assessment, Volume 28, Issue 2, pp. 273-287, 2023

We formulate a hydro-economic model of the North-Western Sahara Aquifer System (NWSAS) to assess the effects of intensive pumping on the groundwater stock and examine the subsequent consequences of aquifer depletion. This large system comprises multi-layer reservoirs with vertical exchanges, all exploited under open access properties. We first develop a theoretical model to account for relevant features of the NWSAS by introducing, in the standard Gisser-Sanchez model, a non-stationary demand and quadratic stock-dependent cost functions. In the second step, we calibrate parameters values using data from the NWSAS over 1955–2000. We finally simulate the time evolution of the aquifer system with exploitation under an open-access regime. We specifically examine time trajectories of the piezometric levels in the two reservoirs, the natural outlets, and the modification of water balances. We find that natural outlets of the two reservoirs might be totally dried before 2050.

Limited‐tenure concessions for collective goodsJournal articleNicolas Quérou, Agnès Tomini et Christopher Costello, Journal of Economic Dynamics and Control, Volume 143, pp. 104484, 2022

We analyze theoretically an institution called a “limited-tenure concession” for its ability to induce efficient public goods contribution and common-pool resource extraction. The basic idea is that by limiting the tenure over which an agent can enjoy the public good, but offering the possibility of renewal contingent on ample private provision of that good, efficient provision may be induced. We first show in a simple repeated game setting that limited-tenure concessions can incentivize socially-efficient provision of public goods. We then analyze the ability of this instrument to incentivize the first best provision for common-pool natural resources such as fish and water, thus accounting for spatial connectivity and growth dynamics of the resource. The duration of tenure and the dispersal of the resource play pivotal roles in whether this limited-tenure concession induces the socially optimal private provision. Finally, in a setting with costly monitoring, we discuss the features of a concession contract that ensure first-best behavior, but at least cost to the implementing agency.

Externality and common-pool resources: The case of artesian aquifersJournal articleHubert Stahn et Agnès Tomini, Journal of Environmental Economics and Management, Volume 109, pp. 102493, 2021

This study examines a specific class of common-pool resources whereby rivalry is not characterized by competition for the resource stock. Artesian aquifers are a typical example of such resources since the stock never depletes, even when part of the resource is extracted. We first propose a dynamic model to account for the relevant features of such aquifers such as the water pressure and well yield and characterize the corresponding dynamics. We then compare the social optimum with the private exploitation of an open-access aquifer. The comparison of these two equilibria highlights the existence of a new source of inefficiency. In the long run, this so-called pressure externality results in an additional number of wells for the same water consumption, thereby raising costs. Finally, we characterize a specific stock-dependent tax to neutralize the pressure externality.

Marine Ecosystem Considerations and Second-Best ManagementJournal articleNicolas Quérou et Agnès Tomini, Environmental & Resource Economics, Volume 70, Issue 2, pp. 381-401, 2018

We compare how the long-run distribution of fishing activities is affected in multispecies fisheries when facing different second-best control rules: (1) species-specific landing regulation, and (2) global input regulation. We show how this depends on the economic returns and on the type of ecological interaction considered. We highlight specifically that fishing effort does not necessarily increase on nontargeted species and decrease on targeted species, and that the characterization of second-best efficient instruments may differ drastically depending on the nature of the interaction.

Private eradication of mobile public badsJournal articleChristopher Costello, Nicolas Quérou et Agnès Tomini, European Economic Review, Volume 94, pp. 23-44, 2017

We consider analytically the non-cooperative behavior of many private property owners who each controls the stock of a public bad, which can grow and spread across spatial areas. We characterize the conditions under which private property owners will control or eradicate, and determine how this decision depends on property-specific environmental features and on the behavior of other landowners. We show that high mobility or lower control by others result in lower private control. But when the marginal dynamic cost of the bad is sufficiently large, we find that global eradication may be privately optimal in these cases, eradication arises in the non-cooperative game and is also socially optimal so there is, in effect, no externality. (C) 2017 Elsevier B.V. All rights reserved.

On conjunctive management of groundwater and rainwaterJournal articleHubert Stahn et Agnès Tomini, Resource and Energy Economics, Volume 49, pp. 186-200, 2017

We consider groundwater managed by a sole owner and where a perfect substitute, rainwater harvesting, is physically connected with the primary water source. This generates a marginal opportunity cost of using rainwater, since harvested water does not infiltrate. We first discuss the conditions that lead to a switch toward rainwater harvesting, then look at long-term rainwater harvesting systems. Due to limited storage capacity, long-term use of rainwater is only possible in conjunction with groundwater. We show that this only arises if the price of water is higher than the full marginal cost of rainwater harvesting. We also provide comparative statics related to this configuration, especially concerning the long-term water table. These results are finally illustrated by numerical examples. (C) 2017 Elsevier B.V. All rights reserved.

On the Environmental Efficiency of Water Storage: the Case of a Conjunctive use of Ground and RainwaterJournal articleHubert Stahn et Agnès Tomini, Environmental Modeling & Assessment, Volume 21, Issue 6, pp. 691-706, 2016

Rainwater harvesting, consisting in collecting runoff from precipitation, has been widely developed to stop groundwater declines and even raise water tables. However, this expected environmental effect is not self-evident. We show in a simple setting that the success of this conjunctive use depends on whether the runoff rate is above a threshold value. Moreover, the bigger the storage capacity, the higher the runoff rate must be to obtain an environmentally efficient system. We also extend the model to include other hydrological parameters and ecological damages, which respectively increase and decrease the environmental efficiency of rainwater harvesting.

Partial enclosure of the commonsJournal articleChristopher Costello, Nicolas Quérou et Agnès Tomini, Journal of Public Economics, Volume 121, Issue C, pp. 69-78, 2015

We examine the efficiency, distributional, and environmental consequences of assigning spatial property rights to part of a spatially-connected natural resource while the remainder is competed for by an open access fringe. We refer to this as partial enclosure of the commons. We obtain sharp analytical results regarding partial enclosure of the commons including: (1) While second best, it typically improves welfare relative to no property rights, (2) all resource users can be made better off, (3) positive rents arise in the open access area, and (4) the resource maintains higher stocks. Under spatial heterogeneity, we also characterize spatial regions that are ideal candidates for partial enclosure — typically, society should seek to enclose those patches with high environmental productivity and high self-retention, but whether high economic productivity promotes or relegates a patch may depend on one's objective.

Remittances and incentive to migrate: An epidemic approach of migrationJournal articleClaire Naiditch, Agnès Tomini et Christian Ben Lakhdar, International Economics, Volume 142, pp. 118-135, 2015

This paper focuses on feedback mechanisms of remittances on the size of the migrant population. We argue that low remittances contribute to relax recipients’ credit constraints and foster further emigration. On the other hand, high remittances may deter migration if they make further emigration unnecessary. Thus, remittances can be considered as a contaminating factor in an epidemic model of migration. This model allows us to characterize a rich set of situations in order to appraise the impact of different policies on the total number of migrants. For instance, we show the mechanisms through which a policy aiming at making migrants successful in the host country may finally lower migration.

Rainwater Harvesting and Groundwater Conservation: When Endogenous Heterogeneity MattersJournal articleRaphaël Soubeyran, Mabel Tidball, Agnès Tomini et Katrin Erdlenbruch, Environmental & Resource Economics, Volume 62, Issue 1, pp. 19-34, 2015

In this paper, we focus on resource conservation in a model of decentralized management of groundwater and rainwater. We show that a conservation policy may have opposite effects on the level of the resource, depending on the outcome of the decentralized management. More precisely, we consider identical farmers who can use two water resources (groundwater and/or rainwater) and we study the symmetric and asymmetric feedback stationary Nash equilibria of the dynamic game. We show that a subsidy on the use of rainwater may increase the level of the aquifer at the symmetric equilibrium, whereas it decreases the level of the aquifer at the asymmetric equilibrium. This suggests that the usual focus on (interior) symmetric equilibria in dynamic games may provide misleading policy implications. Copyright Springer Science+Business Media Dordrecht 2015