Merz et al. (2026) Disentangling the anthropogenic climate change influence on recent hydroclimate whiplash events via multiple nudged model simulations

Identification

• Journal: npj Climate and Atmospheric Science
• Year: 2026
• Date: 2026-10-28
• Authors: Niklas Merz, Jakob Zscheischler A, István Dunkl, Sebastian Sippel, Antonio Sánchez-Benítez, Helge Goessling, Amal John, Frauke Feser, Emanuele Bevacqua
• DOI: 10.1038/s41612-026-01578-3

Research Groups

• Department of Compound Environmental Risks, Helmholtz Centre for Environmental Research - UFZ, Leipzig, Germany
• Department of Hydro Sciences, TUD Dresden University of Technology, Dresden, Germany
• Institute for Meteorology, Leipzig University, Leipzig, Germany
• Alfred Wegener Institute, Helmholtz-Centre for Polar and Marine Research, Bremerhaven, Germany
• Institute of Coastal Systems, Helmholtz-Zentrum Hereon, Geesthacht, Germany

Short Summary

This study quantifies the anthropogenic climate change influence on the intensity of nine recent hydroclimate whiplash events using a multi-model ensemble of wind-nudged simulations, revealing that climate change accounts for an average of 9% of observed whiplash intensity, primarily driven by non-linear increases in potential evapotranspiration.

Objective

• To quantify thermodynamically-driven changes in hydroclimate whiplash intensity for nine high-impact events using the Standardised Precipitation Evapotranspiration Index (SPEI) and a multi-model ensemble of wind-nudged storyline simulations.
• To disentangle the anthropogenic contributions to whiplash intensity arising from changes in precipitation and potential evapotranspiration.

Study Configuration

• Spatial Scale: Nine high-impact regional events across the globe, analyzed on a 0.5° × 0.5° grid.
• Temporal Scale: Recent decade (events from the past decade, e.g., 2017–2024 for event periods); SPEI-3 (3-month moving average) and SPEI-12 (12-month moving average) timescales; calibration periods from 1980–2024 or 1980–2014.

Methodology and Data

• Models used: CESM2, IFS-FESOM, AWI-CM-1, ECHAM6 (all circulation-nudged climate models).
• Data sources: ERA5 global reanalysis dataset (1940–2024), NCEP-NCAR Reanalysis 1 (for ECHAM6 nudging).

Main Results

• Anthropogenic climate change accounts for an average of 9% (range across events: -2% to 72%) of the observed whiplash intensity, with positive contributions for nearly all events according to the multi-model mean.
• This climate change contribution is predominantly driven by a non-linear increase in potential evapotranspiration (PET), which strengthens drying more during the dry phase (mean 12% contribution) than during the wet phase (mean -7% contribution).
• Precipitation changes contribute a smaller and less robust mean signal of 4%.
• Models agree on the positive climate change contribution for six of the nine events (approximately two-thirds).
• Model uncertainty on the magnitude of the climate change contribution is substantial, with an average inter-model spread of 13% across events (9%/°C when normalized by warming level).
• Events in regions dominated by organized deep convection or complex ocean-land interactions (e.g., West Africa, East Africa, Central America) proved most difficult for the nudged simulations to reproduce.

Contributions

• Provides the first quantification of the anthropogenic contribution to the intensity of specific, historically observed hydroclimate whiplash events, complementing previous studies focused on long-term changes in frequency or intensity of generic events.
• Utilizes a unique multi-model ensemble of wind-nudged storyline simulations, which constrains large-scale atmospheric circulation to observations, thereby isolating thermodynamic responses to anthropogenic warming and reducing uncertainty from free-running models.
• Disentangles the contributions of precipitation and potential evapotranspiration, revealing that the asymmetric enhancement of PET (stronger drying during dry phases) is the primary driver of whiplash intensification.
• Highlights the critical importance of employing multiple independently developed nudged datasets to enhance robustness and adequately capture structural uncertainty in event-based attribution analyses of complex events.

Funding

• Program-oriented funding of the Helmholtz Association
• Helmholtz Centre for Environmental Research SEESAW PhD cohort
• German Federal Environmental Foundation (DBU) (AZ: 20025/114)
• Deutsche Forschungsgemeinschaft (DFG) Emmy Noether Programme (grant ID 524780515)
• SMWK (Sächsisches Staatsministerium für Wissenschaft, Kultur und Tourismus) [3-7304/44/4-2023/8846] (Breathing Nature initiative)
• EU Horizon project ‘Artificial Intelligence for Enhanced Representation of Processes and Extremes in Earth System Models’ (AI4PEX; grant agreement 101137682)
• Helmholtz Research Field Earth & Environment for the Innovation Pool Project Actuate
• BMFTR-projects ClimXtreme-A5 (01 LP 2322 B) and WAKOS-2 (01LR2003A1)
• Helmholtz Climate Initiative (HICAM)—Phase 2
• European Union’s ‘Destination Earth’ initiative

Citation

@article{Merz2026Disentangling,
  author = {Merz, Niklas and A, Jakob Zscheischler and Dunkl, István and Sippel, Sebastian and Sánchez-Benítez, Antonio and Goessling, Helge and John, Amal and Feser, Frauke and Bevacqua, Emanuele},
  title = {Disentangling the anthropogenic climate change influence on recent hydroclimate whiplash events via multiple nudged model simulations},
  journal = {npj Climate and Atmospheric Science},
  year = {2026},
  doi = {10.1038/s41612-026-01578-3},
  url = {https://doi.org/10.1038/s41612-026-01578-3}
}