Fast adjustment versus slow SST-mediated response of daily precipitation statistics to abrupt 4xCO 2
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Fast adjustment versus slow SST‑mediated response of daily precipitation statistics to abrupt 4xCO2 Hervé Douville1 · A. John1 Received: 10 July 2020 / Accepted: 3 November 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Projected changes in global to regional precipitation remain highly model-dependent and are driven by both fast atmospheric adjustments and slower ocean-mediated responses to increasing concentrations of greenhouse gases. Understanding the relative influence of these multiple drivers is one of the main objectives of the Cloud Feedback Model Intercomparison Project. Here the focus is on the daily precipitation response to an abrupt quadrupling of atmospheric C O2, as simulated by the CNRM-CM6-1 global climate model. Extended atmosphere-only experiments with prescribed sea surface temperature (SST) are used to decompose the precipitation changes into separate responses to uniform SST warming, the pattern of SST anomalies, as well as fast radiative and physiological CO2 effects. The uniform SST warming dominates the global and regional changes in annual mean and annual maximum daily precipitation intensity. In contrast, the annual mean number of wet days and the annual maximum of consecutive dry days show a strong fast adjustment. They are also sensitive to the SST warming pattern that strongly influences changes in large-scale circulation. The increase in daily precipitation intensity drives the global-mean magnitude of the annual precipitation change. In contrast, the response of wet day frequency shapes the geographical distribution and interannual variability of the annual mean precipitation, especially in the subtropics, and is more sensitive to changes in near-surface relative humidity than in the total water column over land. Although the annual precipitation response does not seem highly sensitive to the base state, these results deserve further investigation and model intercomparison within CFMIP. Keywords Climate change · Precipitation · Drivers · Intensity · Frequency · Extremes
1 Introduction Global warming has long been recognized as a potential threat for food security, given its potential impacts on the mean water cycle, but also on the seasonality and variability of water resources. Nevertheless, projected hydrological changes are still uncertain at both global and regional scales (Stocker et al. 2013; Lehner et al. 2020) and still need to be better understood despite recent advances in this field (Allan et al. 2020). Beyond the expected response of the global and annual mean precipitation to increasing concentrations of greenhouse gases, potential changes in the spatio-temporal
* Hervé Douville [email protected] 1
Centre National de Recherches Météorologiques, Université de Toulouse, Météo-France, CNRS, 42 Avenue Gaspard Coriolis, 31057 Toulouse Cedex 01, France
distribution of daily precipitation rates are a matter of concern given their relevance to adaptation policies. The future change in global-mean precipitation per degree warming,
