A Top-Down Meets Bottom-Up Approach for Climate Change Adaptation in Water Resource Systems

Abstract

The adaptation to the multiple facets of climate/global change challenges the conventional means of water system planning. Numerous demand and supply management options are often available, from which a portfolio of adaptation measures needs to be selected in a context of high uncertainty about future conditions. A framework is developed to integrate inputs from the two main approaches commonly used to plan for adaptation. The proposed “top–down meets bottom–up” approach provides a systematic and practical method for supporting the selection of adaptation measures at 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 prioritized adaptation measures are identified following a bottom-up approach through a participatory process with the relevant stakeholders and experts. Cost-effective combinations of adaptation measures are then selected using a hydro-economic model at basin scale. The resulting adaptation portfolios are climate checked to define a robust program of measures based on trade-offs between adaptation costs and reliability. Valuable insights are obtained on the use of uncertain climate information for selecting robust, reliable, and resilient water management portfolios. Finally, cost allocation and equity implications are analyzed through the comparison of economically rational results (cooperative game theory) and the application of social justice principles.

Integrating climate model projections into environmental risk assessment: A probabilistic modeling approach

“…Two main approaches for regional downscaling are commonly referred to as "top-down" and "bottom-up" (Pulido-Velazquez et al, 2022). The "top-down" approach involves downscaling climate projections from GCMs under a range of emission scenarios to provide inputs, for example, for models that predict impacts and analyze adaptation measures.…”

“…Empirical–statistical downscaling, on the other hand, aims at reproducing similar aspects as those measured, and can also involve stochastic weather models known as weather generators. An alternative or supplement to the top‐down approach is a bottom‐up approach, where vulnerability thresholds and local responses are empirically studied to define locally suitable adaptation strategies (Pulido‐Velazquez et al, 2022). Bottom‐up approaches can make use of local knowledge through participative approaches to foresight future climate scenarios and define locally relevant adaptation strategies.…”

Global Resilience Analysis of Combined Sewer Systems Under Continuous Hydrologic Simulation

“…Therefore, a key shortcoming in the GRA method is the threat (e.g., rainfall) is not linked to the impact (e.g., CSOs). To address this, the threat-based analysis, also called the "top-down" approach (from threats to impacts), can be integrated with middle-state approaches, previously done in climate change adaptation studies (Ekström et al, 2013;Pulido-Velazquez et al, 2022). The top-down approach focuses on the identification of potential threats that could impact the system and has traditionally been used in risk analysis (Butler et al, 2017;Pulido-Velazquez et al, 2022).…”

“…To address this, the threat-based analysis, also called the "top-down" approach (from threats to impacts), can be integrated with middle-state approaches, previously done in climate change adaptation studies (Ekström et al, 2013;Pulido-Velazquez et al, 2022). The top-down approach focuses on the identification of potential threats that could impact the system and has traditionally been used in risk analysis (Butler et al, 2017;Pulido-Velazquez et al, 2022). Integrating the top-down approach into the GRA can thus provide valuable insights to ensure the delivery of the required level of service, particularly when interested in increasing resilience to a particular threat.…”