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Enhanced summer convective rainfall at Alpine high elevations in response to climate warming


Global climate projections consistently indicate a future decrease in summer precipitation over the European Alps1,2,3. However, topography can substantially modulate precipitation change signals. For example, the shadowing effect by topographic barriers can modify winter precipitation change patterns4,5, and orographic convection might also play an important role6,7. Here we analyse summer precipitation over the Alpine region in an ensemble of twenty-first-century projections with high-resolution (12 km) regional climate models8,9 driven by recent global climate model simulations10. A broad-scale summer precipitation reduction is projected by both model ensembles. However, the regional models simulate an increase in precipitation over the high Alpine elevations that is not present in the global simulations. This is associated with increased convective rainfall due to enhanced potential instability by high-elevation surface heating and moistening. The robustness of this signal, which is found also for precipitation extremes, is supported by the consistency across models and future time slices, the identification of an underlying mechanism (enhanced convection), results from a convection-resolving simulation11, the statistical significance of the signal and the consistency with some observed trends. Our results challenge the picture of a ubiquitous decrease of summer precipitation over the Alps found in coarse-scale projections.

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Figure 1: Ensemble average of the projected percentage change in Alpine summer precipitation.
Figure 2: RCM ensemble average of the projected percentage change in different precipitation types and changes in evapotranspiration and potential instability index.
Figure 3: Projected change in summer (June–August) Alpine daily precipitation 95th percentile (R95).


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We thank the CMIP5, EURO-CORDEX and MED-CORDEX modelling groups for making available the simulation data used in this work and the Swiss Federal Office for Meteorology and Climatology for providing the EURO4M-APGD. The work of the ETH group was supported by the Swiss National Sciences Foundation through the Sinergia grant CRSII2_154486 ‘crCLIM’.

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F.G. conceived the study, contributed to the analysis and wrote the paper. C.T., E.C., N.B., C.S. and S.S. contributed to the analysis, the production of figures and the text.

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Correspondence to Filippo Giorgi.

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The authors declare no competing financial interests.

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Giorgi, F., Torma, C., Coppola, E. et al. Enhanced summer convective rainfall at Alpine high elevations in response to climate warming. Nature Geosci 9, 584–589 (2016).

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