Can we trust CMIP5/6 future projections of European winter precipitation?

E Moreno-Chamarro,M J Roberts,L-P Caron,S Loosveldt Tomas,P Ortega

doi:10.1088/1748-9326/abf28a

Abstract

IPCC models project a likely increase in winter precipitation over northern Europe under a high-emission scenario. These projections, however, typically rely on relatively coarse ∼100 km resolution models that can misrepresent important processes driving precipitation, such as extratropical cyclone activity, and ocean eddies. Here, we show that a pioneering 50 km atmosphere–1/12° ocean global coupled model projects a substantially larger increase in winter precipitation over northwestern Europe by mid-century than lower-resolution configurations. For this increase, both the highest ocean and atmosphere model resolutions are essential: only the eddy-rich (1/12°) ocean projects a progressive northward shift of the Gulf Stream. This leads to a strong regional ocean surface warming that intensifies air–sea heat fluxes and baroclinicity. For this then to translate into a strengthening of North Atlantic extratropical cyclone activity, the 50 km atmosphere is essential, as it enables enhanced diabatic heating from water vapor condensation and an acceleration of the upper-level mean flow, which weaken vertical stability. Our results suggest that all recent IPCC climate projections using traditional ∼100 km resolution models could be underestimating the precipitation increase over Europe in winter and, consequently, the related potential risks.

Highlights

IntroductionWinter precipitation is projected to increase over northern and central Europe by the end of the century (likely under the Representative Concentration Pathway, RCP8.5), related to enhanced atmospheric moisture, moisture convergence, and extratropical cyclone activity [1]
Winter precipitation is projected to increase over northern and central Europe by the end of the century, related to enhanced atmospheric moisture, moisture convergence, and extratropical cyclone activity [1]
Our results show that winter precipitation over NW Europe increases notably more in HH than at lower resolutions due to increased extratropical cyclone activity in the North Atlantic

Summary

Introduction

Winter precipitation is projected to increase over northern and central Europe by the end of the century (likely under the Representative Concentration Pathway, RCP8.5), related to enhanced atmospheric moisture, moisture convergence, and extratropical cyclone activity [1]. The magnitude of the change in North Atlantic extratropical cyclone activity and its particular contribution to that precipitation increase remain uncertain [1,2,3]. This is due partly to the sensitivity to model resolution of key processes driving precipitation and atmospheric circulation changes at local and hemispheric scales Sensitivity studies have previously examined the influence of finer model resolutions in the atmosphere and the ocean on the representation of the mean state, variability, and future change of the mid-latitude large-scale atmospheric circulation and precipitation.

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Conclusion