12/3/2023 0 Comments Laurent blancTemporal variations in seasonal precipitation are weaker compared to temperature, even though such apparent quasi-stability can conceal a significant decrease (or increase) in snow (or rain). This is less true in winter, when uncertainties remain almost constant throughout the study period (Supplementary Fig. Although model uncertainties tend to be smaller in summer than in winter under historical radiative forcing, they increase over the current century, denoting differentiated climate sensitivity (that is, different warming under a similar radiative forcing). While RCP4.5 shows a slower increase in temperature for the last decades of the century, RCP8.5 produces an ever-accelerating warming trend. These values are quite similar for the summer warming expected by the end of the century under RCP4.5, but a sensibly larger warming is anticipated for RCP8.5 (+ 8.5 ☌ against pre-industrial simulations, Fig. Future temperature evolution in winter is expected to lead to a warming of + 3.5 ☌ by 2100 against the pre-industrial era under RCP4.5 (i.e. + 2 ☌ during 1965–2018, which is our study period and constrained by observational data availability, and another + 1.5 ☌ between 20), and + 5.5 ☌ under RCP8.5 (Fig. More specifically, they both depict a warming trend, at a comparable rate of roughly + 0.3 to + 0.4 ☌ per decade (i.e. + 1.5 ☌ between 19) in both winter (December–January–February) and summer (June–July–August). By construction, simulations from the historical runs fit observations at the Chamonix weather station in terms of statistical distribution. Catchment area, ice-covered proportion, slope and hypsometric curves are also computed to use as inputs to the hydrological model (Supplementary Methods Sect. These climate variables come from 16 general circulation models (GCMs) under representative concentration pathway (RCP) 4.5 and RCP8.5 36. The climate variables (temperature and precipitation) influencing water discharge in and around the Mont-Blanc Massif are firstly downscaled and post-corrected using the reference Chamonix weather station (1042 m.a.s.l., Fig. These changes will have major effects on river discharges and water quality 19, impacting hydropower generation, agriculture, forestry, tourism and aquatic ecosystems 8, 20. Of particular importance are the relative weight of each of these forcings over the coming years and decades, and their dependency on the greenhouse gas emission scenarios. These changes could either be driven by (i) changes in precipitation 13, 14, especially in the proportion of liquid and solid water 15, 16, depending on the altitude of the 0 ☌ isotherm 17 (ii) a general warming trend, increasing snow and ice melt, hereby contributing to glacier mass loss 18, but also increasing evapotranspiration from the surface (iii) glacier retreat in response to such warming, ultimately leading to changes in water discharge as the available ice reserves gradually decrease 11. In this context, major changes are likely to occur in water discharge 11 in and near these vulnerable regions, mostly decreasing runoff in summer and modifying water resources 12. In the Alps, the cryosphere is crucial for water storage and for contributing to the total discharge of the main major European rivers 10. Global change and temperature increase are projected to lead to major environmental changes in mountainous regions 1, including major changes in glacier extent 2, 3, permafrost 4, ice and snow cover 5, 6, 7, and vegetation 8, 9. These shifts will have significant downstream impacts on water quantity and quality, affecting hydroelectric generation, agriculture, forestry, tourism and aquatic ecosystems. These changes are almost similar according to a scenario with a lower warming (RCP4.5) and are mostly driven by glacier retreat. By contrast, the summer season, currently the most important discharge period, will be marked by a runoff decrease of approximately 40%. By 2100, under RCP8.5 (high-emission scenario), the winter discharge of the Arve river remains low but is expected to increase by 80% when compared to the beginning of the century. For the first time for this region, we have forced a hydrological model with output from an ice-dynamical glacier model and 16 downscaled climate projections, under RCP4.5 and RCP8.5 scenarios. ![]() In this work, we modelled the twenty-first century evolution of runoff in the Arve river, downstream of Mont-Blanc’s French side. By 2100, the impact of climate change on the cryosphere and hydrosphere in the Alps is expected to lead to a decrease in annual river discharge. ![]() The Mont-Blanc massif, being iconic with its large glaciers and peaks of over 4,000 m, will experience a sharp increase in summer temperatures during the twenty-first century.
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