HIGH-MOUNTAIN ENVIRONMENT UNDER CLIMATE CHANGE, THE INTERACTIONS BETWEEN CLIMATE, METEOROLOGY AND GEOMORPHOLOGICAL FACTORS

The Alps, and in general the high mountain areas, in recent decades are under going profound changes due to climate change. The peculiarities and the greater vulnerability of these territories, characterized by complex and delicate balances, are threatened by global warming. In fact, it considerably reduces the habitat of many plant and animal species, pushing them towards ever greater elevations. Once this living zones have reached the tops of the reliefs may no longer be available, and may lead to the disappearance, from these environments, of endemic biodiversity (Hannah et al., 2002). At the same time, however, the progressive debris coverage of the glacial tongues (Deline, 2005; Caccianiga et al., 2011) and the progressive expansion of the proglacial areas, offer new spaces and areas that can be colonised by the vegetation systems and animal communities (Whittaker, 1993). The changes underway in these areas not only affect biological systems, but also geodiversity and the geoheritage of the alpine and mountain environment. “Geodiversity” can be defined simply as “the natural range (diversity) of geological (rocks, minerals, fossils), geomorphological (land form, physical processes) and soil features. It includes their assemblages, relationships, properties, interpretations and systems” (Gray, 2004). For definition of “geodiversity” it follows that an impact on geomorphological processes can affect the local diversity of an area. Examples are the changes in the speed and intensity of processes, such as for example the acceleration of glacial shrinkage, the degradation of permafrost (Deline et al., 2015), the impact of the action of running waters connected to extreme events, the mass wasting processes (Cossart and Fort, 2008; Lane et al., 2017) and the related interactions with biological systems (Eichel, 2015). More in detail in the Alps, but as happens in other mountain ranges, glaciers are shrinking and retreating at ever increasing levels, losing the valley tongues and more and more extensive areas are leaved by the ice. The newly formed proglacial zones are characterized by an abundance of incoherent debris, easily dislocated by the running waters, especially during intense meteorological phenomena (Luino, 2005). These areas, in many cases easily accessible by mountain-goers and not only by expert mountaineers, may therefore present geomorphological dangerous situations, increased by the extremes of meteorological events (for example drought or intense precipitation events). This entails an increase in risks for tourist and even productive activities. The increase in the risk factor for hikers can also derive not only from an increase in danger, for example along the paths, but also from an increase in vulnerability given by sudden changes in weather conditions and the greater difficulty of walking on the paths (Fort, 2015; Pelfini et al., 2007a). The current studies must face the challenge of knowing more in detail the complex interactions that take place in these changing territories, and moreover it is needed to at least partly predict their evolution and behaviour. This challenge has a double value, both scientific, and therefore to broaden the knowledge on the complexity of nature, and civil, because the knowledge of phenomena and the environment allows a more conscious attendance of the high mountain territories. This is the first step for the mitigation of the risk, furthermore, a development that is as environmentally sustainable as possible. Certainly in the coming decades the Alps landscapes will be profoundly different from those of the last century. The progressive reduction of the cryosphere will also have repercussions on many aspects of everyday life of the population that lives not in close contact with the ice giants, but also at a considerable distance from the glacial areas. For example, it has to be considered the availability of drinking water, or the concept of albedo of the snowy areas, a fundamental factor in the climatic feedback processes, or the mountaineering and skiing use of the glaciers. This Doctoral Project fits into this context, that is, to increase knowledge about climatic forcing in high mountain areas and their effect on natural processes. More specifically the attention is focused on the proglacial areas with particular regard to those deglacialized in the last century; but also it was considered the effect of meteorological hazards, like extreme events (mainly rainfall and snowfall) to fragile high-mountain environments. The approach to this study is multifaceted and involves different disciplines: glaciology, geomorphology, dendrochronology, climatology and meteorology, and focuses attention on the interactions between the Earth’s surface and the atmosphere. Particular attention is paid to the meteorological and climatic parameters that can regulate the colonization of proglacial or high mountain areas by pioneer tree species, which are related to the type of substrate, the amount of precipitation, the wind regime to solar radiation and the micrometeorological variables such as sensible and latent heat fluxes (Garavaglia et al., 2010a). The study area focuses on the Forni Valley in high Valtellina (Sondrio, Central Alps, Ortles-Cevedale group), and a comparison with other key sites distributed over the Central-Western Alps, such as Loana Valley in Val Vigezzo (Verbano Cusio Ossola, Central-Western Alps), and the area of Alpe Veglia (Verbano Cusio Ossola, Central-Western Alps, Monte Leone group). These sites are all characterized by a high complexity of orography and different responses to the impacts of climate change. In order to better understand the environment under study, experimental campaigns for measuring meteorological and micrometeorological quantities, were specifically carried out in two of the study sites. The first campaign in the proglacial area of the Forni Glacier, the second in the Alpe Veglia and near the proglacial area of the Aurona Glacier in Val d’Ossola. Both study areas are located in an alpine environment at an altitude between 1740 m a.s.l. of Alpe Veglia and 2552 m a.s.l. of the Forni Glacier, characterised by the absence of vegetation as in the cases of the two proglacial environments, or of pasture with deciduous forest, in the case of Alpe Veglia. The measurement stations installed are equipped both with traditional instruments, such as thermometer, cup anemometer, wind vane, radiometer, barometer and rain gauge, and both with instruments for measuring turbulence in the lowest layer of the atmosphere, or atmospheric boundary-layer, such as the ultrasonic anemometer and the krypton hygrometer. The sites under study, chosen as representative sites of the alpine environment, are characterised by terrain with complex orography, soil, vegetation and degree of anthropization variable in space in a sudden way, and therefore with a dynamics of the atmosphere that is difficult to predict. This has involved the development, parallel to the experimental campaigns, of a numerical modelling both statistical (climatological) and deterministic (meteorological) for the study of the atmosphere and its interaction with the surface. The main points deepened by this work are: a) in the climatology field an indepth study of the precipitation regimes of the last century in the area of the Forni Glacier, and its implications on the run-off and colonization of tree species; b) in the meteorology field an advanced study on atmospheric turbulence measurements in high mountains on the two sites of Alpe Veglia and Forni Glacier. Moreover, thanks to a limited area meteorological model (WRF) it is possible to interpret the dynamics of the atmosphere in detail, always with the aim of correlating the colonization of tree species in the proglacial area and atmospheric processes.