Singular optimal control model of stock dependent environmental policies

In many countries, forest policies consist of a system of various regulations, taxes and subsidies. In this article, we focus on those policies that regulate selective harvesting and study the example of Central Africa. We use a deterministic singular optimal control model of renewable resources to assess these policies with respect to a first best situation which integrates a social surplus or externality function. In particular, in contrast to earlier articles, we analyze a stock dependent tax, for which the objective function is piecewise differentiable. We use a theorem proposed by Hartl and Feichtinger to solve the mathematical problem. We show that this tax is the most flexible instrument with respect to fund collection.Singular optimal control; environmental taxation; renewable resource economics; stock dependency

Des outils en appui aux gestionnaires des inondations : méthodes d'évaluation économiques et implication des habitants. Application à la gestion des inondations sur la basse vallée de l'Orb

National audienceSession 7 Outils: re-questionner l'évaluation. Ce document rassemble trois articles: 1. Des outils en appui aux gestionnaires des inondations : méthodes d'évaluation économiques et moyens d'implication des habitants 2. Comment évaluer les effets de la modélisation participative dans l'émergence d'une gouvernance territoriale ? 3. Démarches participatives et asymétries de pouvoir : éliciter et interroger les positionnement

Dynamic management of water transfer between two interconnected river basins

Identifiant HAL : hal-01006695This paper analyzes the dynamic interaction between two regions with interconnected river basins. Precipitation is higher in one river-basin while water productivity is higher in the other. Water transfer increases productivity in the recipient basin, but may cause environmental damage in the donor basin. The recipient faces a trade-off between paying the price of the water transfer, or investing in alternative water supplies to achieve a higher usable water capacity. We analyze the design of this transfer using a dynamic modeling approach, which relies on non-cooperative game theory, and compare solutions with different information structure (Nash open-loop, Nash feedback, Stackelberg) with the social optimum. We first assume that the equilibrium between supply and demand determines the optimal transfer price and amount. We show that, contrary to the static case, in a realistic dynamic setting in which the recipient uses a feedback information structure the social optimum will not emerge as the equilibrium solution. We then study different leadership situations in the water market and observe that the transfer amount decreases towards a long-run value lower than the transfer under perfect competition, which in turn lays below the social optimum. In consequence, the water in the donor's river-basin river converges to a better quality in the presence of market power. Finally, we numerically compare our results to the Tagus-Segura water transfer described in Ballestero (2004). Welfare gains are compared for the different scenarios. We show that in all dynamic settings, the long-run transfer amount is lower than in Ballestero's static model. Further, we show that the long-run price settles at a lower level than in Ballestero's model, but is still higher than the average cost-based price determined by the Spanish government

Un tour d'horizon des critères d'évaluation de la diversité biologique

Cet article utilise un exemple simple pour passer en revue des concepts de mesure de la biodiversité, avec un effort pour expliciter leurs fondements axiomatiques. L'article offre ensuite un aperçu des concepts développés pour sa protection, et il s'achève sur une discussion de quelques spécificités du problème, comme la prise en compte de certains attributs spatiaux et d'effets de seuils. / This paper provides a review of different methods for measuring biodiversity, with an effort in making explicit their axiomatic foundations. Then, it broaches some concepts of biodiversity protection, and finally it discusses several specificities in this issue, such as the role played by spatial attributes and by threshold effects.ECONOMIE;BIODIVERSITE;CONSERVATION

Optimal adaptation strategies to face shocks on groundwater resources

We consider an exogenous and reversible shock to a groundwater resource, namely a decrease in the recharge rate of the aquifer. We compare optimal extraction paths and the social costs of optimal adaptation in two cases: under certainty, i.e. when the date of occurrence of the shock is known, and under uncertainty, when the date of occurrence of the shock is a random variable. We show that an increase in uncertainty leads to a decrease in precautionary behavior in the short run and to an increase in precautionary behavior in the long run. We apply our model to the particular case of the Western la Mancha aquifer in Spain. We show that, in this context, it is advantageous for the water agency to acquire information on the date of the shock, especially for high-intensity and intermediate-risk events

Une analyse coût-bénéfice spatialisée de la protection contre des inondations. Application de la méthode des dommages évités à la basse vallée de l'Orb

Cet article étudie la pertinence d'une analyse coût-bénéfice (ACB) basée sur la méthode des dommages évités pour évaluer des politiques de prévention des inondations. S'appuyant sur un cas d'étude dans la vallée de l'Orb (Hérault), il détaille les étapes de l'approche, notamment la modélisation des enjeux et le calcul des dommages moyens annuels. Il propose différentes formes de résultats : valeur actuelle nette, carte des dommages potentiels et carte des bénéfices attendus des projets, et montre comment ces résultats peuvent contribuer à la définition de stratégies de gestion des inondations, par exemple en déterminant les crues de projet. La discussion porte sur la transférabilité de la méthode, sur ses limites et les perspectives de développement. / This article explores the relevance of implementing a Cost-Benefit Analysis (CBA) of flood prevention policies via the Damage Avoided approach. Based on a case study in the Orb catchment (Hérault), the article reminds the different steps of the approach, in particular the modelization of assets in floodplains and the calculus of mean annual damages. The article proposes different ways to present the results : the net present value, a map of potential damage and a map of expected benefits, and shows how these results can contribute to the definition of flood management strategies, for example by the choice of design-floods. The discussion deals with the transferability of the method, its limits and perspectives for further developments

La gestion du manque d’eau structurel et des sécheresses en France

Cet article s’intéresse aux politiques et dispositifs de gestion du manque d’eau et des sécheresses en France. La première partie décrit les politiques et dispositifs existants, en distinguant la gestion quantitative des volumes d'eau et la gestion par les prix ainsi que les politiques structurelles et les politiques conjoncturelles. La seconde partie discute des politiques et dispositifs envisageables en France. Cela inclut des politiques incitant aux adaptations au niveau des exploitations, une réforme de la gestion de crise et des dispositifs de tarification et d’échange de droits qui pourraient être différenciés selon les utilisateurs, l’état de la ressource et la situation météorologique. Ces nouveaux dispositifs sont par ailleurs compatibles avec la réforme en cours et la mise en place des organismes uniques de gestion collective (OUGC) à l’échelle locale. / This article deals with policies and management measures addressing water scarcity and droughts in France. The first part describes existing practices, differentiating between quota and pricing instruments and between structural and temporary measures. The second part discusses policies and measures that could be applied in France. It includes policies providing incitation to support farm-level adaptations, a reform of current crisis management and pricing and market measures that could be differentiated depending on the end-user, the state of the resource and the weather conditions. Moreover, these measures fit in the current policy reform and the introduction of local institutions for collective water management, called OUGC

Les réserves de substitution sont-elles une solution à la pénurie d'eau ?

Nestmarks: fine grasses for crosswalls and plug, crinkly paper cocoons, remains of crickets

Using the adaptive cycle in climate-risk insurance to design resilient futures

Assessing the dynamics of resilience could help insurers and governments reduce the costs of climate-risk insurance schemes and secure future insurability in the face of an increase in extreme hydro-meteorological events related to climate change