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Publications

Externality and common-pool resources: The case of artesian aquifersJournal articleHubert Stahn and 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 and 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 and 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 and 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 and 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 and 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 and 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 and 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
Rainwater Harvesting under Endogenous Capacity of Storage: a Solution to Aquifer Preservation?Journal articleHubert Stahn and Agnès Tomini, Annals of Economics and Statistics, Issue 119-120, pp. 209-234, 2015

This paper studies groundwater management in the presence of rainwater harvesting (RWH). We propose a two-state model that takes into account the dynamics of the aquifer and the standard dynamics of the storage capacity, and we assume that the collection of rainwater reduces the natural recharge. We analyze the trade-off between these two water harvesting techniques in an optimal control model. In particular, we show that, when these techniques are perfect substitutes, the development of RWH leads in the long run to a depletion of the water table, even if pumping is reduced. This result is illustrated by a numerical application for the Pecos River Basin (New Mexico, USA). JEL: Q25, C61, D61. / KEY WORDS: Rainwater Harvesting, Conjunctive Use, Groundwater Management, Optimal Control.
Is the Gisser and Sanchez model too simple to discuss the economic relevance of groundwater management?Journal articleAgnès Tomini, Water Resources and Economics, Volume 6, pp. 18-29, 2014

This paper discusses the framing of the model of Gisser and Sánchez (1980) [9] which is commonly reproduced by the follow-up literature. We note that results on the magnitude of welfare gains from optimal groundwater management are affected by the models׳ limitations, such as the commonly used assumption on the linear relationship between pumping cost and the water table level, and the absence of considerations for non-consumptive benefits. We question the appropriateness of these assumptions since the stock effect (the dependence of extraction cost and/or that of benefits on the stock of resource) affects the time variation of the shadow price. We demonstrate that this leads to a declining value of in situ resource over time. As such, its addition on marginal extraction cost may be negligible, and consequently favors the validation of the Gisser-Sánchez effect.