Marginal snowpacks: The basis for a global definition and existing research needs

A marginal snowpack is a recent concept that refers to snow cover that is relatively shallow and transient but still has important environmental and socioeconomic functions. This class of snow cover influences environments over large areas of the world and is very common in the Mediterranean climates, but also in the transition zone between persistent seasonal and ephemeral snowpacks all over the world. However, a globally-accepted definition to identify these environments has not been reached yet. Most of the modelling and monitoring tools for snow have been developed in cold and alpine areas with persistent snowpacks. The study and modelling of shallower snowpacks in milder environments are complicated by their high temporal variability, frequently patchy nature and typical coexistence with shrubs and forest. However, in recent years new remote sensing tools and more complex modelling approaches and specific parametrizations are facilitating their study. This paper provides a definition for marginal snowpacks, identifying them as those with: (i) seasonal peak depths that only occasionally surpass 1.5 m in favorable deposition zones such as wind drifts, ii) having typical seasonal durations ranging from 60 to 120 days, and (iii) that are predominantly in an isothermal state (on >75% of days) with high densification rates and several cycles of accumulation-ablation during each snow season. We review the main existing research challenges to improve scientific capabilities for their study and we discuss their hydrological and environmental relevance at different spatial scales.