Managing water is a grand challenge problem and has become one of humanity's foremost priorities. Surface water resources are typically societally managed and relatively well understood; groundwater resources, however, are often hidden and more difficult to conceptualize. Replenishment rates of groundwater cannot match past and current rates of depletion in many parts of the world. In addition, declining quality of the remaining groundwater commonly cannot support all agricultural, industrial and urban demands and ecosystem functioning, especially in the developed world. In the developing world, it can fail to even meet essential human needs. The issue is: how do we manage this crucial resource in

A B S T R A C TThe high uncertainty associated with the effect of global change on water resource systems calls for a better combination of conventional top-down and bottom-up approaches, in order to design robust adaptation plans at the local scale. The methodological framework presented in this article introduces "bottom-up meets top-down" integrated approach to support the selection of adaptation measures at the river basin level by comprehensively integrating the goals of economic efficiency, social acceptability, environmental sustainability and adaptation robustness. The top-down approach relies on the use of a chain of models to assess the impact of global change on water resources and its adaptive management over a range of climate projections. Future demand scenarios and locally prioritised adaptation measures are identified following a bottom-up approach through a participatory process with the relevant stakeholders and experts. The optimal combinations of adaptation measures are then selected using a hydro-economic model at basin scale for each climate projection. The resulting adaptation portfolios are, finally, climate checked to define a robust least-regret programme of measures based on trade-offs between adaptation costs and the reliability of supply for agricultural demands.This innovative approach has been applied to a Mediterranean basin, the Orb river basin (France). Midterm climate projections, downscaled from 9 General Climate Models, are used to assess the uncertainty associated with climate projections. Demand evolution scenarios are developed to project agricultural and urban water demands on the 2030 time horizon. The results derived from the integration of the bottom-up and top-down approaches illustrate the sensitivity of the adaptation strategies to the climate projections, and provide an assessment of the trade-offs between the performance of the water resource system and the cost of the adaptation plan to inform local decision-making. The article contributes new methodological elements for the development of an integrated framework for decision-making under climate change uncertainty, advocating an interdisciplinary approach that bridges the gap between bottom-up and top-down approaches.

This paper proposes and analyses three policy instruments which can be used to enhance farmers' compliance with individual water allocations in a decentralized management context. Three regulation strategies are proposed for the case of groundwater allocations for irrigation: the first relies on economic instruments; the second is based on tools designed to promote prosocial behaviors; and the third combines assumptions from the first two approaches. They are evaluated through 16 scenario workshops involving 124 stakeholders and farmers in five French groundwater basins. Stakeholders' perceptions are analyzed, disentangling the ethical, economic, institutional, social and technical perspectives underlying the stakeholders' arguments for or against the proposed instruments for groundwater-use regulation. The analysis reveals a preference for the strategy that combines economic and social incentives.

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The case study conducted in this paper looks at residential water pricing from three different points of view. It first describes existing urban water-pricing practices in Southern France, emphasizing that pricing is not yet being used as a tool for providing economic incentives to save water. It then looks at the observed impact of pricing on water consumption, through an econometric analysis of a cross-sectional data set. The analysis suggests that demand, with an estimated price elasticity of -0.2, is not yet very responsive to price variation. A regional water model (300 municipalities) is then developed and used to simulate the potential impact of various water-pricing scenarios on aggregate water demand, aggregate water sales revenue, and consumer surpluses. The results illustrate the trade-offs that have to be made between the search for environmental effectiveness, cost recovery, and equity when implementing complex water-pricing structures such as block rates or seasonal water pricing.