How changements in the circulation patterns specific to the solid precipitations can affect these meteorological events in the Alpine stations of the Mediterranean region ? Use of the ERA5 reanalyses

Abstract

Abstract A classification was achieved to obtain some daily atmospheric circulation types (days that have a similar atmospheric circulation pattern), capable of reproducing sequences specific to the solid precipitations’ events that occur in the mountains of the southern Alps (Mediterranean region). These atmospheric circulation types were statistically studied to get the evolution of the frequency of the synoptic conditions favorable and unfavorable to solid precipitations. The classification produced six atmospheric circulation types, including two synoptic snow classes and two dry classes. The South circulation with a trough on western Europe (STW) is the major snow classes. STW reproduced 62% of the total solid precipitations’ events, 68% of those with a medium intensity level and 100% of those with the high intensity level, which shows the effectiveness of the approach. The total number of days of presence per decades of STW, decreased between 1950 and 2019. This decreasing frequency of occurrence also applies to the other synoptic class of snow, the Depression over Central Europe (DCE). Conversely, the West anticyclonic (WA) and Southwest anticyclonic (SWA), did not produce any solid precipitations events and indicated the opposite logic, with an increase in their occurrences for the same period. This could lead to a strong change in the climate of the South of France, with major impact on the thickness and duration of snow cover. A sharp decrease in snow cover would have heavy economic consequences, the water cycle would be modified, the management of water resources could then be severely called into question and more worryingly, it would increase the intensity of periods of drought. The most plausible explanation for this phenomenon would come from the spread of Hadley's cell, which would push the Azores anticyclone further north and leads to a higher frequency of occurrence of WA and SWA.