Atmospheric rivers responses to climate change in the Mediterranean Region

Moisture transport over the northeastern Atlantic Ocean is one of the processes governing precipitation distribution and variability over Southern Europe. This moisture transport mainly occurs in the so-called Atmospheric Rivers (ARs). ARs are relatively narrow and elongated filaments of high-water vapor transport, which are associated with tropical moisture exports and often occur in combination with the passage of strong extratropical cyclones. Such structures transport more than 90% of the total mid-latitude vertically integrated water vapor, that on landfall, produce precipitation which can be both beneficial and destructive due to its interaction with topography or ascent in the Warm Conveyor Belt.

Understanding how AR characteristics will respond to a warming climate is, therefore, critical to mitigate changes in the intensity of AR-related precipitation and related hydrological extremes.

ARs reaching Southern Europe are analyzed using CMIP5 and CMIP6 simulations and on a high resolution transient simulation between 850 CE to 2100. The projected IVT for 2070–99 significantly exceeds the range given by interannual–interdecadal variability of the last millennium. Changes in IVT are in line with significant increases in tropospheric moisture content, driven by the concurrent rise in surface temperatures associated with the anthropogenic climate trend. On regional scales, recent and projected precipitation changes over the British Isles follow the global positive IVT trend, whereas a robust precipitation decrease over Iberia is identified in the twenty-first century, particularly during autumn. This indicates a possible extension of stable and dry summer conditions and a decoupling between moisture availability and dynamical forcing. The investigation of circulation features reveals a mean poleward shift of moisture corridors and associated atmospheric rivers.

 

Acknowledgments

The financial support for this work was possible through the following FCT project: HOLMODRIVE—North Atlantic Atmospheric Patterns Influence on Western Iberia Climate: From the Late Glacial to the Present (PTDC/CTA-GEO/29029/2017).