Regionally high risk increase for precipitation extreme events under global warming

Daily precipitation extremes are projected to intensify with increasing moisture under global warming following the Clausius-Clapeyron (CC) relationship at about 7%/∘C7%/∘C. However, this increase is not spatially homogeneous. Projections in individual models exhibit regions with substantially larger increases than expected from the CC scaling. Here, we leverage theory and observations of the form of the precipitation probability distribution to substantially improve intermodel agreement in the medium to high precipitation intensity regime, and to interpret projected changes in frequency in the Coupled Model Intercomparison Project Phase 6. Besides particular regions where models consistently display super-CC behavior, we find substantial occurrence of super-CC behavior within a given latitude band when the multi-model average does not require that the models agree point-wise on location within that band. About 13% of the globe and almost 25% of the tropics (30% for tropical land) display increases exceeding 2CC. Over 40% of tropical land points exceed 1.5CC. Risk-ratio analysis shows that even small increases above CC scaling can have disproportionately large effects in the frequency of the most extreme events. Risk due to regional enhancement of precipitation scale increase by dynamical effects must thus be included in vulnerability assessment even if locations are imprecise.

Martinez-Villalobos, C., Neelin, J.D, 2023: Regionally high risk increase for precipitation extreme events under global warming. Sci Rep 13, 5579. https://doi.org/10.1038/s41598-023-32372-3

Figure 1 (a) Example of simulated daily precipitation probability distributions in the historical and global warming (SSP5 8.5) runs in the CNRM-CM6-1 model for the Western United States (30N–48N, 103W–124W). The plot showcases the two leading order probability distribution regimes: an approximately scale-free range controlling the probability of low and moderate daily precipitation values, and a scale-dominated range controlling the large-event tail. The scale 𝑃L is a key parameter controlling the intensity and frequency of extreme daily precipitation events. (b) Multi-model mean of 𝑃L in the CMIP6 historical run (1990–2014). (c) Multi-model mean of the 99.9th wet-day daily precipitation percentile in the CMIP6 historical run (1990–2014). Red boxes show the location of regions used to exemplify behavior in this and remaining figures. The Niño 3.4 region is shown in blue as it overlaps Niño 3 and Niño 4 regions.

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