Multidecadal variability of winter precipitation and snowfall frequencies in a Mediterranean mountain range

The Mediterranean mountains are characterized by having most of its annual precipitation concentrated in winter and in the form of snow. They normally experience a summer drought with drier and hotter summers when compared with other mountain ranges. Therefore, snow is crucial as a water resource in these regions, providing water during the spring snowpack melting. On the other hand, according to the recent IPCC-AR6 report, the Mediterranean is a climate change hot spot, which threatens the future of snow in its mountains. Understanding the variability of winter precipitation and its underlying mechanisms on large time scales allow us to find predictability patterns, and thus to pursue mitigation and adaptation strategies.

This study employs reconstructions of meteorological series from mountain stations in the Iberian Peninsula, utilising a downscaling methodology derived from ERA20C and ERA5 reanalyses. The methodology for reconstruction is based on an analog method, which is presented and discussed. The methods and code for the reconstructions are publicly available.  A comprehensive analysis of the low-frequency variability and trends of the resulting winter precipitation and the frequency of snow days has been conducted for the period 1900-2024. This analysis encompasses the investigation of teleconnection patterns associated with the low-frequency variability of winter precipitation and snowfall, as well as the frequency and nature of synoptic circulation types that lead to orographic precipitation and large-scale precipitation enhancement. The analysis and conclusions presented here provide a more comprehensive understanding of the mechanisms involved in the occurrence of decades with more or less winter precipitation and snowfall frequencies.