Abstract. The frequency and intensity of climate extremes is expected to increase in
many regions due to anthropogenic climate change. In central Europe extreme
temperatures are projected to change more strongly than global mean
temperatures, and soil moisture–temperature feedbacks significantly contribute
to this regional amplification. Because of their strong societal, ecological
and economic impacts, robust projections of temperature extremes are needed.
Unfortunately, in current model projections, temperature extremes in central
Europe are prone to large uncertainties. In order to understand and
potentially reduce the uncertainties of extreme temperature projections in
Europe, we analyze global climate models from the CMIP5 (Coupled Model
Intercomparison Project Phase 5) ensemble for the
business-as-usual high-emission scenario (RCP8.5). We find a divergent
behavior in long-term projections of summer precipitation until the end of
the 21st century, resulting in a trimodal distribution of
precipitation (wet, dry and very dry). All model
groups show distinct characteristics for the summer latent heat flux, top soil
moisture and temperatures on the hottest day of the year (TXx), whereas for
net radiation and large-scale circulation no clear trimodal behavior is
detectable. This suggests that different land–atmosphere coupling strengths
may be able to explain the uncertainties in temperature extremes.
Constraining the full model ensemble with observed present-day correlations
between summer precipitation and TXx excludes most of the very dry
and dry models. In particular, the very dry models tend to
overestimate the negative coupling between precipitation and TXx, resulting
in a warming that is too strong. This is particularly relevant for global warming
levels above 2 ∘C. For the first time, this analysis allows for the substantial reduction of
uncertainties in the projected changes of TXx in global
climate models. Our results suggest that long-term temperature changes in TXx
in central Europe are about 20 % lower than those projected by the multi-model
median of the full ensemble. In addition, mean summer precipitation is found
to be more likely to stay close to present-day levels. These results are
highly relevant for improving estimates of regional climate-change impacts
including heat stress, water supply and crop failure for central Europe.