Characterizing major avalanche episodes in space and time in the twentieth and early twenty-first centuries in the Catalan Pyrenees

Abstract

8With the aim of better understanding avalanche risk in the Catalan Pyrenees, the present work focuses on the analysis of 9 major (or destructive) avalanches. For such purpose major avalanche cartography was made by an exhaustive 10 photointerpretation of several flights, winter and summer field surveys and inquiries to local population. Major avalanche 11 events were used to quantify the magnitude of the episodes during which they occurred, and a Major Avalanche Activity 12Magnitude Index (MAAMI) was developed. This index is based on the number of major avalanches registered and its 13 estimated frequency in a given time period, hence it quantifies the magnitude of a major avalanche episode or winter. 14 Furthermore, it permits a comparison of the magnitude between major avalanche episodes in a given mountain range, or 15 between mountain ranges, and for a long enough period, it should allow analysis of temporal trends. Major episodes from 16 winter 1995/96 to 2013/14 were reconstructed. Their magnitude, frequency and extent were also assessed. During the last 17 19 winters, the episodes of January 22-23 and February 6-8 in 1996 were those with highest MAAMI values, followed by 18 January 30-31, 2003, January 29, 2006, and January 24-25, 2014. To analyze the whole twentieth century, a simplified 19 MAAMI was defined in order to attain the same purpose with a less complete dataset. With less accuracy, the same 20 parameters were obtained at winter time resolution throughout the twentieth century. Again, 1995/96 winter had the highest 21 MAAMI value followed by 1971/72, 1974/75 and 1937/38 winter seasons. The analysis of the spatial extent of the different 22 episodes allowed refining the demarcation of nivological regions, and improving our knowledge about the atmospheric 23 patterns that cause major episodes and their climatic interpretation. In some cases, the importance of considering a major 24 avalanche episode as the result of a previous preparatory period, followed by a triggering one was revealed. 25 Key words 26Major avalanche, major avalanche episode, Pyrenees, magnitude, frequency, hazard, risk.

Characterisation of Extreme Precipitation Events in the Pyrenees: From the Local to the Synoptic Scale

“…Both its marked topography and its location between two climatically differentiated basins, the Mediterranean and Atlantic basins, mean that this mountain area presents a highly variable climate. The precipitation variability in this area has been extensively studied [1][2][3] since it is clearly associated with different natural hazards in the 2 of 16 Pyrenees, such as avalanches [4][5][6], heavy snowfall [7][8][9], or flood events [10][11][12], among many others.…”

The Avalanche of Les Fonts d’Arinsal (Andorra): An Example of a Pure Powder, Dry Snow Avalanche

“…Between 28th January and 8th February, two successive and well-differentiated meteorological episodes were recorded in the Pyrenees. This meteorological sequence contributed to form a snowpack with a high intrinsic instability that triggered many major avalanches in the Pyrenees [6,12], among them the Percanela and LFd'A, in Andorra. Previously, at the Arinsal ski resort (1927 m a.s.l.…”

“…In the Catalan area of the range, from December 1995 to March 1996, the snowfalls doubled and even tripled the means calculated over a period of thirty years at half a dozen observatories, and the avalanche situation of 1996 was considered the most catastrophic of the second half of the 20th century [4]. Furthermore, the episodes of 22nd to 23rd January and 6th to 8th February attained the highest Major Avalanche Activity Magnitude Index values ever recorded (this index records quantification of the magnitude of episodes during which major avalanche events have occurred [6]). In Andorra, on 8th February 1996, large avalanches occurred on the slopes of the Valira del Nord valley, including Arinsal and the Casamanya peak; in the Madriu and Valira d'Orient valleys, including the Incles, Ransol, Vall del Riu and Montaup valleys [7,8] and above Andorra la Vella [9].…”

Characterization of Extreme Precipitation Events in the Pyrenees. From the Local to the Synoptic Scale.

“…Both its marked topography and its location between two climatically differentiated basins, the Mediterranean and Atlantic basins, mean that this mountain area presents a highly variable climate. The precipitation variability in this area has been extensively studied [1][2][3], since it is clearly associated with different natural hazards in the Pyrenees, such as avalanches [4][5][6], heavy snowfall [7][8][9], or flood events [10][11][12], among many others.…”