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Products: Roumasset, James

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Do Natural Disasters Make Sustainable Growth Impossible?

We consider the prospects for sustainable growth using expected utility models of optimal investment under threat from a natural disaster. Extension of a discrete, two-period model, to continuous time over an infinite time horizon permits the analysis of sustainability under uncertainty regarding adverse events, including both one-time and recurrent disasters. Natural disasters, with destruction of productive capital, disrupt the optimal consumption and utility paths, but the Arrow et al. (2004) sustainability criterion is still satisfied even without adding strong or weak sustainability constraints. We also consider a separate natural resource sector and show that, except for extreme cases, the optimal steady state level of the renewable resource is not affected by the possibility of natural disasters. In the case of catastrophic events, however, damage to the resource system may be severe enough to push the system below a critical value tipping point, undermining the prospects of long-run sustainability.


Filipino 2040: Environmental Resources, Shocks, and National Well-Being

The contribution of the environmental-resource sector to national well-being is the sum of natural resource depletion and environmental degradation. Inasmuch as existing resource stocks are below efficient levels, better enforcement of existing laws as well as policies that incentivize sustainable use are needed. Similarly, progressive royalty assessment of mineral resources can incentivize exploration without transferring the bulk of resource rents to private interests. In the case of pollution, the key is to face firms with the full costs of their production, e.g. through emission taxes and/or cap and trade systems. Calculating total depletion and degradation (TDD) will facilitate the calculation of green national income (GNI), a more inclusive metric of national well-being. In the same way, simultaneous optimization of disaster management policies in the face of climate change can facilitate a further improvement in national well-being, this time measured as comprehensive national income (CNI).


Incentivizing interdependent resource management: watersheds, groundwater, and coastal ecology

Managing water resources independently may result in substantial economic losses when those resources are interdependent with each other and with other environmental resources. We first develop general principles for using resources with spillovers, including corrective taxes (subsidies) for incentivizing private resource users. We then analyze specific cases of managing water resources, in particular the interaction of groundwater with upstream or downstream resource systems.

Published version: Burnett, Kimberly, Sittidaj Pongkijvorasin, James Roumasset, and Christopher A. Wada. "Incentivizing interdependent resource management: watersheds, groundwater and coastal ecology". Handbook of Water Economics. Cheltenham, UK: Edward Elgar Publishing, 2015. Print.


Groundwater Economics without Equations

In many parts of the world, irrigation and groundwater consumption are largely dependent on groundwater. Minimizing the adverse effects of water scarcity requires optimal as well as sustainable groundwater management. A common recommendation is to limit groundwater extraction to maximum sustainable yield (MSY). Although the optimal welfare-maximizing path of groundwater extraction converges to MSY in some cases, MSY generates waste in the short and medium term due to ambiguity regarding the transition to the desired long-run stock level and failure to account for the full costs of the resource. However, the price that incentivizes optimal consumption often exceeds the physical costs of extracting and distributing groundwater, which poses a problem for public utilities facing zero excess-revenue constraints. We discuss how the optimal price can be implemented in a revenue-neutral fashion using an increasing block pricing structure. The exposition is non-technical. More advanced references on groundwater resource management are also provided.


The Good, Bad, and Ugly of Watershed Management

Efficient management of groundwater resource systems requires careful consideration of relationships — both positive and negative — with the surrounding environment. The removal of and protection against “bad” and "ugly" natural capital such as invasive plants and feral animals and the enhancement of “good” capital (e.g. protective fencing) are often viewed as distinct management problems. Yet environmental linkages to a common groundwater resource suggest that watershed management decisions should be informed by an integrated framework. We develop such a framework and derive principles that govern optimal investment in the management of two types of natural capital — those that increase recharge and those that decrease recharge — as well as groundwater extraction itself. Depending on the initial conditions of the system and the characteristics of each type of natural capital, it may make sense to remove bad capital exclusively, enhance good capital exclusively, or invest in both activities simultaneously until their marginal benefits are equal.


Optimal Joint Management of Interdependent Resources: Groundwater vs. Kiawe (Prosopis pallida)

Local and global changes continue to influence interactions between groundwater and terrestrial ecosystems. Changes in precipitation, surface water, and land cover can affect the water balance of a given watershed, and thus affect both the quantity and quality of freshwater entering the ground. Groundwater management frameworks often abstract from such interactions. However, in some cases, management instruments can be designed to target simultaneously both groundwater and an interdependent resource such as the invasive kiawe tree (Prosopis pallid), which has been shown to reduce groundwater levels. Results from a groundwater-kiawe management model suggest that at the optimum, the resource manager should be indifferent between conserving a unit of groundwater via tree removal or via reduced consumption. The model’s application to the Kona Coast (Hawai‘i) showed that kiawe management can generate a large net present value for groundwater users. Additional data will be needed to implement full optimization in the resource system.


Integrating Demand-Management with Development of Supply-Side Substitutes

Sustaining water availability at current prices in the face of growing demand and declining resources is not possible, and scarcity is further exacerbated by falling recharge levels due to climate change, urbanization, and watershed depreciation. We discuss an integrated approach to water-resource development based on principles of sustainability science. In addition to demand management such as pricing, we consider supply-side substitutes such as desalination and wastewater recycling. The importance of integrating demand- and supply-side approaches is especially evident in the case of watershed conservation as climate adaptation. Watershed conservation reduces scarcity by improving groundwater recharge. Yet, incorrect pricing can waste those potential gains. We discuss a joint management strategy, wherein block prices for groundwater consumption and co-determined prices for watershed conservation incentivize and finance efficient profiles of both.


Ordering Extraction from Multiple Aquifers

Optimal groundwater extraction satisfies the condition that the marginal benefits of water consumption equal the full marginal cost of extraction in each period, including the opportunity cost of future benefits foregone. But how should this well-known condition be generalized when there are multiple aquifers available? We provide an extension of the “Pearce equation” to guide the optimal ordering of resource extraction and an illustrative application wherein it is optimal to extract from the “leakiest” aquifer first, letting another aquifer increase in volume. This generalized least cost-first principle contrasts strongly with the sustainable yield approach. By including spatial dimensions, the model provides the marginal valuations of water at each time and place, such that full marginal cost pricing can incentivize users to implement the efficient program. While an untrammeled water market would fail to provide the optimal solution, regulators can facilitate efficient water trading by setting appropriate exchange rates.


Intergenerational Equity with Individual Impatience in an OLG Model of Optimal and Sustainable Growth

Among the ethical objections to intergenerational impartiality is the violation of consumer sovereignty given that individuals are impatient. We accommodate that concern by distinguishing intra- and inter-generational discounting in an OLG model suitable for analyzing sustainability issues. Under the assumption of constant elasticity of marginal felicity, the optimum trajectory of aggregate consumption is guided, via the Ramsey condition, by the intergenerational discount rate but not the personal discount rate. In an economy with produced capital and a renewable resource, intergenerational neutrality results in a sustained growth path, without the necessity of a sustainability constraint, even in the presence of intragenerational impatience. We also find that green net national product remains constant along the optimal approach path to golden rule consumption.

Published version: Endress, L.H., Pongkijvorasin, S., Roumasset, J., Wada, C.A., 2013. Intergenerational equity with individual impatience in a model of optimal and sustainable growth. Resource and Energy Economics. In Press.


A dynamic approach to PES pricing and finance for interlinked ecosystem services: Watershed conservation and groundwater management

A theory of payment for ecosystem services (PES) pricing consistent with dynamic efficiency and sustainable income requires optimized shadow prices. Since ecosystem services are generally interdependent, this requires joint optimization across multiple resource stocks. We develop such a theory in the context of watershed conservation and groundwater extraction. The optimal program can be implemented with a decentralized system of ecosystem payments to private watershed landowners, financed by efficiency prices of groundwater set by a public utility. The theory is extended to cases where land is publicly owned, conservation instruments exhibit non-convexities on private land, or the size of a conservation project is exogenous. In these cases, conservation investment can be financed from benefit taxation of groundwater consumers. While volumetric conservation surcharges induce inefficient water use, a dynamic lump-sum tax finances investment without distorting incentives. Since the optimal level of conservation is generated as long as payments are correct at the margin, any surplus can be returned to consumers through appropriate block pricing. The present value gain in consumer surplus generated by the conservation-induced reduction in groundwater scarcity serves as a lower bound to the benefits of conservation without explicit measurement of other benefits such as recreation, biodiversity, and cultural values.


Published Version: Roumasset, J., Wada, C.A., 2013. A dynamic approach to PES pricing and finance of interlinked ecosystem services: Watershed conservation and groundwater management. Ecological Economics. 87, 24-33.




The Economics of Groundwater

We provide synthesis of the economics of groundwater with a focus on optimal management and the Pearce equation for renewable resources. General management principles developed through the solution of a single aquifer optimization problem are extended to the management of multiple resources including additional groundwater aquifers, surface water, recycled wastewater, and upland watersheds. Given an abundant (albeit expensive) substitute, optimal management is sustainable in the long run. We also discuss the open-access equilibrium for groundwater and the conditions under which the Gisser-Sanchez effect (the result that the present value generated by competitive resource extraction and that generated by optimal control of groundwater are nearly identical) is valid. From the models and examples discussed, one can conclude that optimization across any number of dimensions (e.g. space, time, quality) is driven by a system shadow price, and augmenting groundwater with available alternatives lessens scarcity and increases welfare if timed appropriately. Other rules-of-thumb including historical cost recovery, independent management of separate aquifers, and maximum sustainable yield are inefficient and may involve large welfare losses.

Working Paper

Islands of Sustainability in Time and Space

We review the economics perspective on sustainable resource use and sustainable development. Under standard conditions, dynamic efficiency leads to sustainability of renewable resources but not the other way around. For the economic‐ecological system as a whole, dynamic efficiency and intergenerational equity similarly lead to sustainability, but ad hoc rules of sustainability may well lead to sacrifices in human welfare. We then address the challenges of extending economic sustainability to space as well as time and discuss the factors leading to optimal islands of preservation regarding renewable resources. Exogenous mandates based on moral imperatives such as self‐sufficiency and strong sustainability may result in missed win‐win opportunities that could improve both the economy and the environment, as well as increase social welfare across generations.


Efficient Management of Coastal Marine Nutrient Loads with Multiple Sources of Abatement Instruments

Pollution management based on marginal abatement costs is optimal only if those abatement costs are specified correctly. Using the example of nitrogen pollution in groundwater, we show that the marginal abatement cost function for any given pollution source can be directly derived from a social-welfare maximization problem, wherein controls include both abatement instruments and inputs to pollution-generating production of a good or service. The solution to the optimization model reveals that abatement instruments for each source should be used in order of least marginal abatement cost, and the sources should in turn abate in order of least cost. The least-cost result remains optimal, even when the abatement target is exogenously determined.

Working Paper

Ordering Renewables: Groundwater, Recycling and Desalination


Optimal recycling of minerals can be thought of as an integral part of the theory of the mine. In this paper, we consider the role that wastewater recycling plays in the optimal extraction of groundwater, a renewable resource. We develop a two-sector dynamic optimization model to solve for the optimal trajectories of groundwater extraction and water recycling. For the case of spatially increasing recycling costs, recycled water serves as a supplemental resource in transition to the steady state. For constant unit recycling cost, recycled wastewater is eventually used as a sector-specific backstop for agricultural users, while desalination supplements household groundwater in the steady state. In both cases, recycling water increases welfare by shifting demand away from the aquifer, thus delaying implementation of costly desalination. The model provides guidance on when and how much to develop resource alternatives.


Optimal Provision and Finance of Ecosystem Services: the Case of Watershed Conservation and Groundwater Management

Payments for ecosystem services should be informed by how both the providing-resource and the downstream resource are managed. We develop an integrated model that jointly optimizes conservation investment in a watershed that recharges a downstream aquifer and groundwater extraction from the aquifer. Volumetric user-fees to finance watershed investment induce inefficient water use, inasmuch as conservation projects actually lower the optimal price of groundwater. We propose a lump-sum conservation surcharge that preserves efficient incentives and fully finances conservation investment. Inasmuch as proper watershed management counteracts the negative effects of water scarcity, it also serves as adaptation to climate change. When recharge is declining, the excess burden of non-optimal watershed management increases.

working paper


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