Comment on tc-2021-145

Abstract

The regulating role of glaciers on 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 m a.s.l.). We observed an average reduction of annual snow accumulation due to wind erosion of 2 · 103 kg m−2 y−1 to be compared with a mean annual precipitation of about 2.7 · 103 kg m−2 y−1. The conserved accumulation is made up mainly of snow deposited between April and September, when temperatures above melting point are also observed. End of year snow density, instead, increased in 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 number of melt layers. The computation of snowmelt in the model as a solely function of air temperature may therefore be one of the reasons of the observed mismatch between model and observations.