Is winter precipitation change over Europe underestimated in current climate projections?

Abstract:

It is well accepted that winter precipitation over Northern Europe will increase over this century if greenhouse gas concentrations continue rising. This projection has generally been made using coupled climate models at relatively coarse resolution—usually ~100 km in both the atmosphere and ocean in most IPCC models. This resolution is, however, inadequate to represent critical processes driving precipitation, such as orography, storm structure, or ocean eddies. Higher resolution models are therefore commonly seen as a promising way forward to overcome such limitations. Our study provides evidence that such limitations are indeed real: We find that the global coupled model HadGEM3-GC3.1 at a pioneering 50-km-atmosphere–1/12°-ocean global resolution 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 resolutions are essential: On the one hand, only the eddy-rich (1/12°) ocean projects a progressive northward shift and warming of the Gulf Stream. On the other, only the 50-km atmosphere can translate such warming into strengthened North Atlantic extratropical cyclone activity through enhanced diabatic heating and eddy-driven jet. Our findings suggest that climate projections relying on traditional ~100-km-resolution models might underestimate the precipitation increase over Europe in winter and, consequently, the related potential risks.