A local model of snow–firn dynamics and application to the Colle Gnifetti site

Abstract

Abstract. The regulating role of glaciers in catchment run-off is of fundamental importance in sustaining people living in low-lying areas. The reduction in glacierized areas under the effect of climate change disrupts the distribution and amount of run-off, threatening water supply, agriculture and hydropower. The prediction of these changes requires models that integrate hydrological, nivological and glaciological processes. In this work we propose a local model that combines the nivological and glaciological scales. The model describes the formation and evolution of the snowpack and the firn below it, under the influence of temperature, wind speed and precipitation. The model has been implemented in two versions: (1) a multi-layer one that considers separately each firn layer and (2) a single-layer one that models firn and underlying glacier ice as a single layer. The model was applied at the site of Colle Gnifetti (Monte Rosa massif, 4400–4550 ma.s.l.). We obtained an average reduction in annual snow accumulation due to wind erosion of 2×103 kgm-2yr-1 to be compared with a mean annual precipitation of about 2.7×103 kgm-2yr-1. The conserved accumulation is made up mainly of snow deposited between April and September, when temperatures above the melting point are also observed. End-of-year snow density, instead, increased an average of 65 kg m−3 when the contribution of wind to snow compaction was added. Observations show a high spatial and interannual variability in the characteristics of snow and firn at the site and a correlation of net balance with radiation and the number of melt layers. The computation of snowmelt in the model as a sole function of air temperature may therefore be one of the reasons for the observed mismatch between model and observations.

Snow Multidata Mapping and Modeling (S3M) 5.1: a distributed cryospheric model with dry and wet snow, data assimilation, glacier mass balance, and debris-driven melt

“…Considering firn may also extend the applicability of S3M to polar re-gions, where for example firn-storage capacity is an important factor in determining the long-term fate of the Greenland ice sheet (Forster et al, 2014;Machguth et al, 2016). In this regard, Banfi and De Michele (2022) have recently proposed a local model of snow-firn transition for a binary-mixture snowpack like that considered in S3M.…”

“…The cryosphere is a decisive driver of the Earth system (Barry, 2011;Beniston et al, 2018). Besides altering surface albedo and so concurring with the regulation of global temperature (Flanner et al, 2011), snow and glaciers accumulate winter precipitation and release it during the warm, spring and summer seasons, when demand by societies and ecosystem services is comparatively high (Barnett et al, 2005). This shift in water supply supports water, food, and energy security across climates (Viviroli et al, 2007), with key societal implications (Sturm et al, 2017).…”

“…F. Avanzi et al: The S3M cryospheric model Seasonality between winter accumulation and summer melt (Barnett et al, 2005), compounded by equally complex but more short-term processes such as rain on snow (Rössler et al, 2014), challenges decision makers like water-resource or hydropower managers, who need early and diverse information about snow and glacier-ice amount, distribution, and melt timing to make accurate decisions on water use, allocation, and storage (Georgakakos et al, 2004;Anghileri et al, 2016;Avanzi et al, 2018). This need has catalyzed the development of a variety of models to predict snowmelt-and ice-melt-driven discharge (DeWalle and Rango, 2011) to the extent that cryosphere modeling is a dominating topic of both basic and applied contemporary geosciences (Dozier et al, 2016).…”