Description

Ensemble boosting uses targeted re-initialization of rare weather and climate extremes in large ensembles of fully-coupled Earth System Models. Ensemble boosting starts from simulated extreme events in fully-coupled GCM simulations that are reinitialized about 5-25 days before their peak intensity event of the simulated event, using tiny round-off perturbations. Thereby, targeted large ensembles of extreme events in the climate model can be produced in order to efficiently sample the most extreme events.

Ensemble boosting can successfully generate plausible storylines of extremes that are coherent in space and time. Ensemble boosting can produce good analogue events for record-shattering heatwaves, very cold extremes, large-scale precipitation events, seasonal to multi-year drought events and spatially co-occurring events. Model-based storylines developed with ensemble boosting can be used to study processes that distinguish moderate heatwaves from very extreme ones.

Potential users

Broad communication (public), specific sectors potentially interested (energy, health, …) with critical infrastructure that needs to be resilient to very high return level extremes

Guide

Required background knowledge is high and the tool requires access to High-Performance Computing Facilities (requires capacity to run CESM2 in a bit-for-bit reproducibility). For the use in adaptation and planning pre-existing simulations need to be bias adjusted.

Use cases

• Has been used in parallel with Stochastic weather generators and importance sampling to investigate the unprecedented events of Paris 50C and the 1962/63 cold winter.
• Extremely cold winter season
• 5-day heatwaves in Pacific Northwest, US Midwest and western Europe
• Multi-year drought in Europe and North America
• Winter heavy precipitation event in Germany

References

Sippel, S., Barnes, C., Cadiou, C., Fischer, E., Kew, S., Kretschmer, M., Philip, S., Shepherd, T.G., Singh, J., Vautard, R. and Yiou, P., 2024. Could An Extremely Cold Central European Winter Such As 1963 Happen Again Despite Climate Change?. Weather and Climate Dynamics, 5, pp.943-957.

Fischer, E.M., Beyerle, U., Bloin-Wibe, L., Gessner, C., Humphrey, V., Lehner, F., Pendergrass, A.G., Sippel, S., Zeder, J. and Knutti, R., 2023. Storylines for unprecedented heatwaves based on ensemble boosting. Nature Communications, 14(1), p.4643.

Gessner, C., Fischer, E.M., Beyerle, U. and Knutti, R., 2021. Very rare heat extremes: quantifying and understanding using ensemble reinitialization. Journal of Climate, 34(16), pp.6619-6634.

Gessner, C., Fischer, E.M., Beyerle, U. and Knutti, R., 2023. Developing Low‐Likelihood Climate Storylines for Extreme Precipitation Over Central Europe. Earth’s Future, 11(9), p.e2023EF003628.

Gessner, C., Fischer, E.M., Beyerle, U. and Knutti, R., 2022. Multi-year drought storylines for Europe and North America from an iteratively perturbed global climate model. Weather and Climate Extremes, 38, p.100512.

Lüthi, S., Huber, V., Pascal, M., Beyerle, U., Pyrina, M., Domeisen, D., Vicedo-Cabrera, A.M. and Fischer, E., 2024. Storylines for month-long heatwaves and associated heat-related mortality impacts over Western Europe, in review.

Thompson et al, the 2021 heavy precipitation extreme in Northwestern Germany (in preparation)