Mountain climate variability and its influence on permafrost and frost weathering in Central and S-E European mountain ranges

Abstract

<p>The evolution of discontinuous mountain permafrost presently preserved in high-altitude central and SE European mountain ranges can be regarded as an indicator of climate warming. Considering recent climate scenarios, these areas are prone to become the expression of the transition from inactive to relict landforms, with potential impact on hydrologic regimes and related hazards intensity. The last two decades document permafrost existence and ground thermal regime in rock glaciers and rockwalls in the highest massifs of the Carpathian and the Balkan mountains, with several studies also assessing ground temperature response to both warming and snow regime changes in periglacial areas from the Eastern Alps. The objective of this research is to evaluate multidecadal patterns of temperature and precipitation indices relevant for possible impacts on mountain periglacial landforms in Central and S-E European ranges.</p> <p>Available continuous climate data were used from meteorological stations situated above 2000 m altitude in: a) Tatra Mts (Chopok, 2007 m; Lomnicky Stit, 2635 m); b) Julian Alps (Sonnblick, 3111 m; Kredarica, 2515 m); c) the Southern Carpathians (Vf Omu, 2505 m) and d) Rila Mts (Musala, 2927 m). We check for similarities between trends at regional scale and validate inferred influences through in-situ data series focusing on snow cover variability retrieved from ground temperatures. Specifically, in-situ measurements of permafrost and freezing ground indicators from rock glaciers and rockwalls in the Southern Carpathians were used to give an estimate of permafrost condition and duration of seasonal frost in comparison to thermal and pluvial variations. Ground surface freezing index (<em>Fi</em>) during the cold snow-free interval was considered a particularly important index and was also assessed using data from the Southern Carpathians and Rila Mountains meteorological stations for comparison and validation.</p> <p>The preliminary results on climate variability analysis in the selected mountain ranges show that mean annual air temperature values are increasing in all locations with similar mean rates (approximately 0.032 °C/yr). Both warm and cold season thermal regimes contribute to this trend, with only slight inter-site differences. The variability of solid and liquid annual precipitations and the monthly multiannual analysis of data highlights distinct pluvial patterns correspondent to local topo-climatic characteristics of each mountain range. The rain/snow ratio expresses a direct impact on permafrost and frozen ground by the reduction of the snow cover period and increasing of the warm snow free interval, which enables exchanges between ground and warm atmosphere and potentially disturbs the thermal balance of ground-preserved ice. Specifically, the <em>Fi</em> values are shown to be recently reducing, which equals with a lowering ground cooling degree before the onset of the isolating snow cover. This is also reflected by other changing cold season characteristics, i.e. duration of snow-free and zero-curtain intervals, snow-cover thickness and seasonal frost duration. In such changing conditions, periglacial landforms in the mountain ranges from Central and S-E Europe would be exposed to inactivation which questions the medium to long-term preservation of permafrost.</p>