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

Abstract

Global climate projections consistently indicate a future decrease in summer precipitation over the European Alps^1,2,3. However, topography can substantially modulate precipitation change signals. For example, the shadowing effect by topographic barriers can modify winter precipitation change patterns^4,5, and orographic convection might also play an important role^6,7. Here we analyse summer precipitation over the Alpine region in an ensemble of twenty-first-century projections with high-resolution (∼12 km) regional climate models^8,9 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.