2017/18 WINTER BALANCES OF GLACIERS IN LOMBARDY REGION (CENTRAL ITALIAN ALPS)

Transcription

1 2017/18 WINTER BALANCES OF GLACIERS IN LOMBARDY REGION (CENTRAL ITALIAN ALPS) Data from the Glaciological Service of Lombardy (SGL) network R. Scotti 1,2, B. Di Mauro 3 1 Department of Biological, Geological and Environmental Sciences (BiGeA), University of Bologna, Bologna, Italy 2 Glaciological Service of Lombardy (SGL), Milan, Italy 3 Earth and Environmental Sciences Department, University of Milano-Bicocca, Milan, Italy Abstract In this report, winter mass balances of eight glaciers in the Lombardy region (Central Italian Alps) are presented for the season 2017/2018. Data were provided by the Glaciological Service of Lombardy (Servizio Glaciologico Lombardo, SGL) network. The 2017/18 point winter balances in the Lombardy region are the most negative since 2007 in terms of snow depth, and since 2012 in terms of SWE. We also evaluate the possible effect of Saharan dust deposition in decreasing snow albedo and hence in increasing snow melting. In fact, despite an average precipitation sum from October to May, the very high air temperature of the late spring and the concurrent Saharan dust deposition promoted an early start of the snowmelt that lowered both snow depth and SWE values at the typical time of accumulation measurements. 1

2 Snowfall report from September 2017 to May 2018 The accumulation season 2017/18 started in September with some early snowfalls that were able to stop the glacier melting occurred during the summer of The rest of the autumn was dry with 60 % of precipitation (compared to the average) at the reference weather station (Sils/Maria, Engadin, CH) (Fig. 1). Snowfall events became more frequent from December to February resulting in a + 33 % of winter precipitation, this was crucial to increase the snowpack depth up to the long-term average (Fig. 2). A very different situation occurred in the northern side of the Alps where a series of severe snowfalls resulted in exceptional winter accumulations. Conversely, in the southern side of the Alps, the cumulative sum of snowfall was close to the average of the last decade (Fig. 2). Fig. 1. Cumulative monthly precipitation at the long-term climatic station of Sils/Maria (Upper Engadin, CH, 1799 m a.s.l.) The minimum, maximum and mean values refer to the series (source meteoswiss). The spring snowfall events were clustered in the first half of the season, so that the maximum snow depth on glaciers occurred around mid-april, around 1 month earlier than expected (Fig. 2). The slightly spring precipitation surplus (+ 15%) was counterbalanced by an early start of the snowmelt. In particular, during the second half of April both an impressive heatwave and a concurrent Saharan dust deposition forced an early snow pack transition from winter to hysothermic conditions (Fig. 2). Very high air temperature conditions followed in May and June causing the highest sum of Positive Degrees Day at Lupo Glacier in 10 years (Fig. 4). This situation directly induced strong melting that easily explains why the winter balances on Lombardy glaciers were below the climatic average. 2

3 Fig. 2 The 2017/18 winter season timeline at Bernina Pass (Motta Bianca AWS, series , source SFL Davos). After a very dry period in October and November, the snowfall events increased the snow depth to the average, and, from March to April, above the average. The very fast snowmelt occurred from mid-april to May caused the snowpack to vanish 1 month before the average. Fig. 3. The Suretta Peak and the Suretta Sud glacier (Spluga/Lej sector). The snow cover at Jan 28, 2018 is around the long term average (Ph., R. Scotti) 3

4 Fig. 4. Cumulative Positive Degree Day (PDD) from April 1, 2018 at the Bivacco Corti weather station (2509 m a.s.l. at Lupo Glacier Orobie sector- source SGL). The minimum, maximum and mean values refer to the series. Fig. 5. Glacier ice melting started early in June at the Fellaria glacier (Bernina sector). Saharan dust is particularly concentrated on the frozen surface of the proglacial lake (Ph., R. Scotti ). 4

5 Winter balances 2017/18 The point winter balance measurements on the eight selected glaciers in Lombardy region (SGL network) highlight the Pizzo Scalino glacier as the one with the deepest snowpack (415 cm). Snow depth was below the average in each site ranging from 3% (Pisgana Ovest) to 26% (Campo Nord) with an average regional value of 18% (Fig. 8) Glacier Coordinate (WGS84-UTM Z32N) Elevation and sector (m a.s.l.) Date HS Snow depth (cm) Snow density densità (kg/m³) Snow Water Equivalent (m w.eq) HN difference from average (%) HS Snow depth average (cm) and time series Suretta Sud m Spluga ,2-19% operators P. Gallo, S. Negroni, S. Marchese, A. Borghi, A. Ialongo 400 ( )* Vazzeda m Disgrazia operators M. Butti & co ,7-11% 379 ( )** Pizzo Scalino m Scalino operators A. Bolis, G. Neri ,3 n.d. 456 ( ) Campo Nord Alpe Sud Dosegù Pisgana Ovest m Livigno operators D. Colombarolli, A. Bera, S. Colombarolli m Ortles - Cevedale ,7-26% ,9-25% operators M. Fioletti, L. Bonetti (ARPA Lombardia Centro Nivo-Meteorologico di Bormio) m Ortles - Cevedale n.d. n.d. n.d. n.d. operators M. Fioletti, L. Bonetti (ARPA Lombardia Centro Nivo-Meteorologico di Bormio) m Adamello ,3-3% operators P. Pagliardi, M. Binda, M. Izzo, T. Romanelli, F. Mazzuoleni, A. Ghezzi, A. Lendvai 197 ( )* 214 ( )*** 179 ( )**** 275 ( )* Lupo m Orobie % operators R. Scotti, F. Olivotti, S. Roverato, M. Mazzolini, R. Porta, M. Ruffoni, F. Fazzini 460 ( ) Tab. 1. Point balance data from the SGL glaciers network in (* missing 2002, ** missing 1997, *** missing 2012, **** missing years from 2002 to 2006) The observed point Snow Water Equivalent (SWE) values confirms the snow depth analysis: the highest SWE value was recorded at Pizzo Scalino glacier (2.2 m w.eq) followed by the Suretta Sud glacier (2.2 m w.eq). The homogenous series of SWE values started in In figure 7, SWE was compared with the snow depth series in the same time-interval ( ). It results that the 2017/18 negative SWE anomaly ( 14%) is less dramatic compared with the snow depth anomaly ( 24 %). This is caused by the relatively high snow density that partly counterbalanced the snow accumulation shortage. This represents a very different situation compared to the previous winter season (2016/17) when a late spring series of snowfall events counterbalanced a pronounced winter snow accumulation shortage, but, due to the low density of the fresh snow, did not completely recover SWE deficit. 5

6 Fig. 6. Point snow depth series from the 8 glaciers of the SGL network. 6

7 Fig. 7. Snow depth anomaly (HS) in percentage compared to the average. The anomaly value represents the average of 6 glaciers. (Exceptions: 3 glaciers: 1998 and 2002; 4 glaciers: 1999; 5 glaciers: 2012 and 2018). Fig. 8. Snow depth (HS) and Snow Water Equivalent (SWE) anomaly in percentage compared to the average. The anomaly value represents the average of 6 glaciers. (Exceptions: 3 glaciers: 1998 and 2002; 4 glaciers: 1999; 5 glaciers: 2012 and 2018). 7

8 Fig. 9 a, b. Snow pit at Vazzeda glacier (Left) and Lupo glacier (right). Ph. M. Butti ( ) e F.Olivotti-S.Roverato ( ). Saharan dust is clearly visible on the top of the snowpack. Fig. 10 a, b. Snow pit at Campo Nord-Paradisin glacier (Ph. D. Colombarolli-A. Bera ). 8

9 Fig. 11. The Pisgana Ovest glacier show from the Monte dei Frati summit (Ph. A. Lendvai, ). Fig. 12. Snow depth in 6 selected glaciers with the distribution of the stratigraphic Saharan dust layers. The surface layer is certainly referred to the April 15 dust event while the March 15 and the Feb 8 attributions are uncertain. The timings of the deposition were determined using the NMMB/BSC-dust model. The lack of observed dust on the surface of Suretta Sud glacier can be explained with the modelled distribution pattern of the April 15 dust deposition (Fig. 13). The glacier is located in the Northwest corner of the region and may have been sheltered from the South-East currents that promoted the dust deposition. 9

10 The 2017/18 point winter balances on Lombardy region glaciers are the most negative since 2007 in terms of snow depth, and since 2012 in terms of SWE (Figs 8 and 9). Despite an average precipitation sum from October to May, the very high air temperature of the late spring and the concurrent Saharan dust deposition (that decreases snow albedo) promoted an early start of the snowmelt that lowered both snow depth and SWE values at the typical time of accumulation measurements (end of May). The timings of Saharan dust events were confirmed using the NMMB/BSC-Dust model (an example in Figure 13). It is known that these events reduce snow albedo, increasing the snow grain size and directly promoting the phase transition during the melting season. Figure 13. Dust AOD forecasted using the NMMB/BSC-dust model for the large Saharan dust event of April 15th. The model is operated by the Barcelona Supercomputing Center ( Starting from such a negative situation, in order to achieve an equilibrium glacier net balance, the climatic conditions in the next two months needs to be particularly cold and snowy. Therefore, we expect yet another negative year in term of glacier mass balance in Lombardy region. Report date: The Glaciological Service of Lombardy (Servizio Glaciologico Lombardo) is a non-profit organization of volunteers that deals with the Lombardy region glaciers survey since