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.

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边缘积雪：全球定义和现有研究需求的基础

边际积雪是一个新概念，指的是相对较浅且短暂的积雪，但仍然具有重要的环境和社会经济功能。此类积雪影响世界大片地区的环境，在地中海气候中非常常见，而且在世界各地持续季节性积雪和短暂积雪之间的过渡区也很常见。然而，尚未达成全球公认的识别这些环境的定义。大多数雪建模和监测工具都是在具有持续积雪的寒冷和高山地区开发的。温和环境中较浅积雪的研究和建模由于其高时间变化、频繁的斑块性质以及典型的与灌木和森林共存而变得复杂。然而，近年来新的遥感工具和更复杂的建模方法以及特定的参数化正在促进他们的研究。本文提供了边缘积雪的定义，将其识别为具有以下特征的积雪：(i) 在风流等有利沉积区，季节性峰值深度偶尔超过 1.5 m，ii) 典型的季节性持续时间为 60 至 120 天，以及(iii) 主要处于等温状态（>75%的天数），具有高致密化率，并且在每个雪季期间有多个积累-消融周期。我们回顾了现有的主要研究挑战，以提高其研究的科学能力，并讨论了它们在不同空间尺度上的水文和环境相关性。