Projected elevation-dependent warming in the Alps: contrasting free-atmosphere and surface trends with surface energy balance drivers

Abstract. Because of topography, climate change exhibits complex regional imprints in the Alps. This study aims at understanding the processes that link elevation-dependent warming (EDW) – i.e. the modulation of temperature trends with elevation – at seasonal scale in the Alps with the surface energy balance. We investigate projected EDW patterns in the Alps using 7 km resolution simulations spanning the period 1961–2100 made with the Modèle Atmosphérique Régional (MAR), exploring scenarios SSP2-4.5 and SSP5-8.5 and driven by two general circulation models, EC-Earth3 and MPI-ESM1-2-HR. We find a larger yearly warming signal at high elevations (1.2 to 1.5 °C °C−1 of global warming) than at low elevations (1.1 to 1.3 °C °C−1 of global warming), with contrasted seasonal patterns and intensities (up to 2 °C °C−1 of global warming at high elevations in summer). EDW profiles are found to be different near the surface than in the free atmosphere. Near the surface, a maximum warming is found in spring at mid-elevations that is migrating to higher elevations in summer and autumn. This signal is not found in the free atmosphere. The elevation of the maximum warming is moving upward, consistently with the snowline migration over the years in a warming climate. Investigating surface energy balance trends reveals a link between the profiles of EDW and those of net shortwave radiation and energy used to melt snow. The snow-albedo feedback linked to the net shortwave radiation trend is found to be responsible for two thirds of the impact of the snowline on warming, while snow melt accounts for the last third. Melting limits the warming at high elevation when snow is persisting. We suggest that snow melting is an important driver of EDW that should be considered in any EDW-snow investigations.