Work

GCM Selection and Ensemble Design: Best Practices and Recommendations from the EURO-CORDEX Community

Year: 2025

Type: article

Abstract: High-resolution climate information is critical for the Vulnerability, Impacts, Adaptation, and Climate Services (VIACS) communities. Coordinated ensembles generated by initiatives like the Coordinated Regional Climate Downscaling Experiment (CORDEX) provide consistent and comparable information for the present and future over all land areas of the globe. This manuscript focuses on the European CORDEX initiative (EURO-CORDEX) and its coordinated effort to build regional climate ensembles for the years to come. In its first phase, EURO-CORDEX produced a rich ensemble of regional climate simulations under different representative concentration pathway scenarios. The EURO-CORDEX dataset is openly available and was fed into the Regional Atlas of the IPCC Sixth Assessment Report. However, this ensemble suffered from several shortcomings, which the community seeks to address in the next phase of production. Chief among these is the oft-cited criticism that the selection of GCMs that provide input to the regional climate models was not rigorous and that the resulting ensemble represents an “ensemble of opportunity.” The present paper provides a description of how the community has addressed these shortcomings. We present a comprehensive, flexible, and traceable evaluation framework and toolkit for assessing the suitability of GCMs for downscaling, using EURO-CORDEX as an example. Its value lies in its explicit recognition of subjectivity and mechanisms implemented to transparently track decision-making. Further, the utility of the framework extends well beyond predownscaling decisions to also include postdownscaling investigations performed by the VIACS communities and beyond, to include researchers investigating such topics as model biases, future constraints, and exploring future storylines. Significance Statement The European Coordinated Regional Climate Downscaling Experiment initiative (EURO-CORDEX) community has created a comprehensive evaluation framework and open-source toolkit for global climate model assessment. These approaches provide a robust, transparent, and traceable approach to both pre- and postdownscaling ensemble designs whose utility extends well beyond the immediate regional climate community. This will enable improved and more nuanced assessments of regional climate change and its impacts.

Source: Bulletin of the American Meteorological Society

DOI: 10.1175/bams-d-23-0189.1