Impact of weather type variability on winter precipitation, temperature and annual snowpack in the Spanish Pyrenees

The annual frequency of the occurrence of 10 discriminated weather types were summarized using a principal component analysis that revealed 4 different prevailing winter conditions affecting the Spanish Pyrenees. Northeasterly and easterly flows lead to dry and cold winters where snow only accumulates on northern slopes and mainly in the central Pyrenees. North and northwesterly flows favor wet and cold winters and an increase of snow accumulation in the western Pyrenees and on the northern slopes at lower elevations. Cyclonic and westerly flows favor an increase in precipitation and snow accumulation in all the Pyrenees at lower elevations and cold winters. Finally, southerly flows are associated with milder conditions and high precipitation in the central sector of the Pyrenees, where snow only accumulates at high elevations. For most stations, there were no significant trends in precipitation or temperature during the current reference climatic period (1981-2010), which was in agreement with the lack of observed principal component trends during the same period. Focusing on the shorter 1985-2010 period for which snow data were available, snow depth at mid-March demonstrated significant positive trends associated with an increase in westerly, southwesterly and cyclonic weather during this period. The results demonstrate that the changes in precipitation, temperature and snow accumulation are clearly related to changes in circulation patterns, which are the main driver of temporal fluctuations in the considered climatologies.