International Snow Science Workshop Grenoble – Chamonix Mont-Blanc - 2013 How short warm events disrupt snowcover dynamics Example of a polar basin – Spitsberg, 79°N Éric Bernard 1 , Florian Tolle 1 , Jean Michel Friedt 2 , Christelle Marlin 3 , Madeleine Griselin 1 1 CNRS UMR ThéMA, université de Franche-Comté, Besançon, France 2 CNRS FEMTO-ST, université Franche Comté, Besançon, France 3 CNRS UMR IDES, université Paris-Sud, Orsay, France RESUME : L’Arctique est un indicateur pertinent des changements climatiques. Les dynamiques nivologiques sont directement affectées mais le suivi des processus est rendu délicat par leur rapidité alors qu’ils correspondent à des éléments clef. Ces observations ont pu être conduites sur le glacier Austre Lovén (Spitsberg, Norvège – 79°N) pendant le programme hydro-sensors-FLOWS. Pour mieux comprendre l’impact de ces phénomènes, des observations à échelle spatio-temporelle extrêmement fine ont été menées. Un réseau d’échantillonnage dense (36 points répartis sur 4,5 km 2 ) installé sur le glacier a permis de mesurer différents paramètres : manteau neigeux à plusieurs reprises, bilan de masse, températures au pas de temps horaire. De plus, un réseau de 6 stations photo automatiques permet la cartographie précise du manteau neigeux. Les résultats ont montrés que l’impact de courts événements chauds sur les dynamiques nivo-glaciologiques était capital. La tendance observée ets plus due à un manque de froid l’hiver qu’à un été trop chaud. Un été doux et sec aura une incidence minimale, alors qu’un hiver doux et très arrosé sera extrêmement néfaste aux basses altitudes alors qu’il participera à une importante recharge neigeuse en altitude, au-delà de l’isotherme 0°C. MOTS-CLEF : Changements climatiques, Arctique, dynamiques nivologiques, géomatique. ABSTRACT: Arctic is a reliable indicator of global climate changes. Snow dynamics are directly affected, and following processes becomes challenging: some fast but key events can be missed since they are short but significant. Such observations have been made in the Austre Lovén basin (Spitsbergen, Norway – 79°N) during the Hydro-sensor-FLOWS program. To better understand the impact of climate changes, one approach is to use a fine scale monitoring protocol based on a high density network of sampling points. This has been carried out for 5 years on the Austre Lovén glacier. Overall, 36 measurement points have been distributed at regular intervals over the 4.5 km² glacier surface. For each of these points the snow cover was measured several times and mass balance was yearly recorded. Furthermore, temperature is measured over a 20 sensors network on the glacier, and at last, a network of 6 automated digital cameras is used to map snowcover dynamics. Results show that there is a strong impact of short warm events on snow and ice dynamics. The observed trend is more due to lack of cold in winter than by excess of warm in summer. A meanly warm and dry summer will have few incidence, when a warm and watered winter could be seen as detrimental at low altitude as it will contribute to an important snow refill of the glaciers over the 0°C isotherm. KEYWORDS: Climate change, Arctic, snow dynamics, geomatic. . 1 INTRODUCTION Climate changes are studied in the Arctic for a long time, but mostly at a large spatio- temporal scale. Several processes observed led us to adopt a scale of observation that is as thin as possible. This is what was done on the small polar glacier Austre Lovén in Spisteberg in the framework of the Hydro-sensor-FLOWS internationnal programm. Results concerning more specifically the impact of seasonal climate variations on the snowpack will be developed here. The goal is to show that brutal variation, even short, can challenge the results of a complete hydrological year. 2 GEOGRAPHICAL SETTINGS AND FIELDWORK 2.1 Geographical environnement The Archipelago of Spitsbergen is part of Svalbard, which consists of all islands located between 74° and 80° N and 10° and 35° E. Overall, 60% of the land area is covered by glaciers and it represents about 10% of the total Arctic small glaciers area (Hagen et al., 2003). Similarly to what is observed in the whole Arctic, it is very reactive to climate change: all ______________________ Éric Bernard, CNRS, Laboratoire ThéMA, Université de Franche-Comté, France; tel: +0033 (0)6 89 73 42 11 email: eric.bernard@univ-fcomte.fr 1226