Sensitivity of tropical precipitation extremes to climate change

Precipitation extremes increase in intensity over many regions of the globe in simulations of a warming climate1–3. The rate of increase of precipitation extremes in the extratropics is consistent across global climate models, but the rate of increase in the tropics varies widely, depending on the model used3. The behaviour of tropical precipitation can, however, be constrained by observations of interannual variability in the current climate4–6. Here I show that, across state-of-the-art climate models, the response of tropical precipitation extremes to interannual climate variability is strongly correlated with their response to longer-term climate change, although these responses are different. I then use satellite observations to estimate the response of tropical precipitation extremes to the interannual variability. Applying this observational constraint to the climate simulations and exploiting the relationship between the simulated responses to interannual variability and climate change, I estimate a sensitivity of the 99.9th percentile of daily tropical precipitation to climate change at 10% per K of surface warming, with a 90% confidence interval of 6–14% K−1. This tropical sensitivity is higher than expectations for the extratropics3 of about 5% K−1. The inferred percentage increase in tropical precipitation extremes is similar when considering only land regions, where the impacts of extreme precipitation can be severe. Increases in precipitation extremes (defined here as high percentiles of daily precipitation) associatedwith climate changewould have important impacts, such as on flooding, soil erosion, and landslides7,8. Changes in the distribution of precipitation are expected in a warmer climate because of the dependence of the saturation vapour pressure of water on temperature3,9,10. Observations suggest that precipitation extremes may have increased in intensity as the climate warmed in recent decades, at least regionally11,12. Extratropical precipitation extremes consistently increase at close to the ‘thermodynamic’ rate (∼6%K−1) in simulations with global climate models, corresponding to little change in the magnitude of vertical winds associated with the extremes3. The thermodynamic rate is similar in the tropics, but the simulated rate of increase of tropical precipitation extremesmay be substantially lower or higher depending on the model used, with close to no change in some models and rates of increase of up to 30%K−1 in others3. This inter-model scatter probably results from the strong dependence of tropical precipitation on moist-convective processes that must be represented by subgrid parameterizations in global climate-change simulations13. Recent idealized studies of radiative-convective equilibrium using models that resolve convective-scale dynamics found that intense precipitation increases with warming at close to the thermodynamic rate14,15, but a different response could occur in the tropics because of convective organization and large-scale dynamics that were not included in the idealized studies.