Improvements in the estimation of glacier surface mass balance taking into account albedo decay parameters

The search for satellite-derived proxies of the surface mass balance (SMB) of glaciers is of crucial importance for an updated estimation of the SMB worldwide. The minimum mean  glacier albedo (αmin, calculated as the minimum mean albedo over the whole glacier) attained along a season has proved to be a good proxy. In this work we demonstrate that SMB estimations can be improved by adding albedo decay parameters as predicting variables. The SMB of Hurd glacier (Livingston Island, Antarctica) has been continuously monitored since 2001, with available values of annual, summer and winter SMB. MODIS MOD10A1 daily snow albedo product with a spatial resolution of 500 m over the glacier was downloaded using the Google Earth Engine Application Programming Interface. Data from 2000-2001 to 2020-2021 season are considered in this work. MOD10A1 data were filtered using a maximum filter followed by a first-order Butterworth filter. Each season extends from September to March of two consecutive years. The seasonal albedo was fitted to an exponential decay α=αm+Aexp(-βt), and parameters αm, A and β as well as the albedo decay duration (D) were calculated for all pixels. Mean values of αm, β, A and D were calculated over the whole glacier. Monthly and seasonal mean αmin were also estimated from MOD10A1 data. Simple linear regressions show that the minimum albedo in the period January-February explains the summer SMB, while the minimum albedo in the period December-January explains the annual SMB. Multiple linear regression models including snow albedo decay parameters improve the quality of the models, increasing the value of the coefficient of determination and decreasing the root mean square difference between measured and predicted SMB. These results show that the SMB is determined not only by αmin but also by how fast and for how long the albedo decay takes place, and by the difference between the minimum albedo and the surface albedo at the beginning of the season. On the other hand, most of the snow albedo decay takes place in the period from late September to December. Previous investigations of mass balance over the Hurd Peninsula have established that the snow melt in Hurd Peninsula takes place mostly from December to March. The fact that snow melting lags behind albedo decay can be explained if we consider that some surface snow metamorphic processes occur prior to melting and that melting continues after surface snow has attained its maximum degree of metamorphism.