Integrating top–down and bottom–up approaches to design global change adaptation at the river basin scale

Abstract

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.

Cambio climático y planificación hidrológica: ¿es adecuado asumir un porcentaje único de reducción de aportaciones para toda la demarcación?

“…En este contexto, la región Mediterránea emerge como un punto de especial incidencia del cambio climático (Diffenbaugh y Giorgi, 2012), proyectándose reducciones en la precipitación media anual, aumentos en la evapotranspiración a consecuencia del incremento de la temperatura, veranos más secos y mayor riesgo de episodios de sequía, reduciéndose la recarga de los acuíferos y la escorrentía superficial (Howard, 2011). No obstante, existe una alta incertidumbre respecto a los impactos del cambio climático en la respuesta hidrológica de las cuencas mediterráneas, debida a la elevada dispersión de las señales climáticas simuladas por diferentes modelos (Deidda et al, 2013;Girard et al, 2015). En cualquier caso, se espera que los impactos negativos del cambio climático afecten principalmente a las zonas semiáridas con escasez de agua y un balance frágil entre recursos hídricos y demandas (Estrela et al, 2012) El proceso más común para evaluar los impactos del cambio climático en los recursos hídricos combina el uso de proyecciones climáticas con la modelización hidrológica.…”

A Probabilistic Risk Assessment of the National Economic Impacts of Regulatory Drought Management on Irrigated Agriculture

“…This is consistent with previous studies assessing climate change impacts on water availability for irrigation in England, looking at both license use and abstraction restrictions (Rio et al, ). Adaptive responses in drought management to reduce the impacts will require the integration of changes to top‐down regulatory approaches with bottom‐up farmer and agricultural sector decisions (Girard et al, ; Holman & Trawick, ).…”

A Participatory Approach for Adapting River Basins to Climate Change

“…A combination of quantitative and qualitative methods could be pursued to better integrate stakeholders in the process for adaptation planning. Quantitative (modeling) methods could help to assess the impact of climate change and other relevant factors on water resources and its adaptive management over a range of climate projections, while locally-relevant adaptation measures could be identified through a participatory process with the relevant stakeholders and experts [52]. This scoping of relevant options would narrow down the total number of options that could be subject to a detailed quantitative analysis in a next step.…”

“…Thus, combining qualitative stakeholder-based approaches, such as ours, with more quantitative approaches is a promising avenue to better integrate stakeholders in adaptation planning, while considering uncertain future conditions [25,52].…”