Disentangling the anthropogenic influence on the intensity of recent hydroclimate whiplash events via multiple nudged climate simulations

Hydroclimate volatility describes large and/or rapid swings between extremely dry and extremely wet conditions that can compound impacts on human and ecological systems by clustering extremes in time. Although the basic theoretical link between warming and increased precipitation volatility has long been recognised, our understanding about the magnitude and physical mechanisms behind broader definitions of hydroclimate volatility remains limited.

We employ a ‘hydroclimate whiplash’ metric based on the Standardised Precipitation–Evapotranspiration Index (SPEI) and focus on high-impact events (n=9) building upon the framework established by Swain et al. (2025) to assess anthropogenic contributions to changes in whiplash intensity. Specifically, we use circulation-nudged simulations from three different climate models under present-day and pre-industrial forcing, following a storyline approach. By constraining the large-scale circulation to observations, nudged simulations enable the analysis of observed rare extreme events with a high signal-to-noise ratio while also allowing a comparison across datasets. Furthermore, prescribing the dynamical component in this way isolates the thermodynamic response to anthropogenic forcing, which is crucial, as thermodynamic processes are the predominant driver of changes in hydroclimate volatility. The simulations are evaluated against observations to ensure that spatial patterns, seasonal variability, and temporal correlations are realistically represented across the regions.

Preliminary results show a robust anthropogenic increase in whiplash intensity across most events, albeit with substantial event-to-event heterogeneity. Decomposition into precipitation and potential evapotranspiration (PET) components indicates that the most consistent signal arises from PET-driven drying during the dry phase, reflecting a thermodynamic warming response that enhances atmospheric evaporative demand. Precipitation-related contributions can also be substantial but are more event specific.

This research provides the first multi-model attribution of hydroclimate whiplash intensity, demonstrating that the anthropogenic influence can be detected in rare and complex compound extremes using circulation-nudged storyline climate models.

References:

Swain, D.L., Prein, A.F., Abatzoglou, J.T., Albano, C.M., Brunner, M., Diffenbaugh, N.S., Singh, D., Skinner, C.B. & Touma, D. (2025). Hydroclimate volatility on a warming Earth. Nature Reviews Earth & Environment, 6(1), 35-50.