Finding Storm Track Activity Metrics That Are Highly Correlated with Weather Impacts. Part II: Estimating Precipitation Change Associated with Projected Storm Track Change over Europe

The extratropical storm tracks cause much of the high-impact weather in the midlatitudes, and thus it is of interest to examine the weather impacts of projected storm track change. Here, a framework for quantifying storm track impact on precipitation over Europe developed in Part I for winter is extended to all four seasons and applied to estimate the precipitation impacts of CMIP5 and CMIP6 model projected storm track change under the high-emission scenarios. For autumn and winter, a significant portion of the projected decrease in precipitation over southern Europe and the Mediterranean Sea region can be related to a projected decrease in storm track activity over these regions. In winter, the projected increase in storm track activity near the British Isles accentuates the precipitation increase over that region. In summer, a projected storm track decrease over northern Europe is expected to give rise to a decrease in precipitation that expands the projected drying region poleward and reduces the impact of the projected high-latitude precipitation increase related to the increase in atmospheric moisture. CMIP6 models project stronger drying than CMIP5 models over central and northern Europe in summer and autumn. Part of this increased drying can be related to an enhanced decrease in storm track activity projected by CMIP6 models. Apart from multimodel mean projections, different model projected storm track change patterns can give rise to very different regional precipitation impacts, and account for the model spread in precipitation projection in many regions. What causes such model diversity should be further examined.