Changing European Hydroclimate under a Collapsed AMOC in the Community Earth System Model

Abstract. The Atlantic Meridional Overturning Circulation (AMOC) is expected to weaken or even collapse under anthropogenic climate change. Given the importance of the AMOC in the present-day climate, this would potentially lead to substantial changes in the future projections of the impacts of climate change on regional weather, which is highly relevant for society. Precipitation rates over Europe are expected to decrease under an AMOC collapse, potentially affecting the European hydroclimate. Here, we analyse the impacts of different AMOC collapse and climate change scenarios on the European hydroclimate in a unique set of AMOC experiments executed with the fully-coupled Community Earth System Model (CESM). In general, drier hydroclimatic conditions are expected under an AMOC collapse. The dominant drivers of this change depends on the specific combination of AMOC strength and radiative forcing. In AMOC collapse scenarios under pre-industrial conditions the dominant driver are reduced precipitation rates over the entire European continent. AMOC collapse in combination with increased radiative forcing (RCP4.5, RCP8.5) also leads to higher potential evapotranspiration rates, which further exacerbates the noted shifts to increased seasonal drought (extremes). Here, AMOC collapse enhances well-documented shifts to a drier summer climate in Europe in 'standard' projections of future climate change. In summary, these results indicate a considerable influence of the AMOC on future European hydroclimate. It is therefore vital that climate change projections of European hydroclimate for the (far) future consider the possibility of AMOC changes, and the exacerbated effects this would have on projected regional hydrological changes and consequences for ecosystems and society.