The recent rise in temperature studied on altitudinal level in the Italian eastern Alps

Mountain regions are important sources of fresh water providing the majority of the downstream river flows. In this respect it is important to know the magnitude of the expected changes in the climate at high compared to low elevations in mountain regions. Several attempts were made in the past with rather conflicting results. Temperature rise over the last decades was observed to occur at a faster rate at low compared to high elevation sites in the Swiss alps (Philipona, 2013) but the opposite was found for the Austrian alps (EITZINGER, J., KERSEBAUM, K.C., FORMAYER, H., 2009 ). Our study considered the data of 23 weather stations located exclusively in Trentino (Eastern Italian alps) at elevations ranging from 70 to 2125 m. Mean monthly air temperatures of each station were used to calculate the rate of change in the mean annual and seasonal temperatures over the period 1975 - 2010, and the results show a significantly lower increment rate in high elevation regions compared to the lower elevation sites (0.1°C per decade at high elevation versus 0.5 °C per decade at low elevation). The interpretation of such large difference is not simple. Changes in atmospheric moisture content of the planetary boundary layer may have indeed caused faster warming at low elevations due to enhanced local greenhouse effect, but also multidecadal-scale changes in land use may have contributed substantially. Fast urbanization that occurred at low elevation modified surface albedo as well as the ratio between sensible and latent heat fluxes, possibly leading to accelerated warming. Changes in snow cover, permafrost and glacier surfaces that occurred at high elevations may have also had a role. But at the same time, rapid reforestation of formerly mountain pasture land (+12%) that occurred at high elevations and that was associated to a large and significant increase in mountain forest stocks may have increased evapotranspiration rates. Our study considers in particular this second aspect, by exploring differences in the water vapour fluxes of different mountain land use (meadows, forests and bogs) to finally evaluate, in quantitative terms, the likely changes in evapotranspiration that occurred over the study period. Although a conclusive evidence of land use contribution to the reduced increase in air temperature could not be found, our study elucidates and emphasizes the potential role of mountain forests in climate change mitigation associated to a faster water cycle, role that was often ignored in previous studies.