Quantifying snow sublimation by Eddy covariance measurements on the High Atlas Mountain of Marrakech at Tazaghart plateau, Morocco

Mountains areas are often a valuable source of water supply in semi-arid watersheds and play an important role in the hydrologic processes and water balance. Precipitation in high altitude areas is important and forms a seasonal snowpack where water is stored during winter. Therefore, an accurate assessment of sublimation is essential in the overall hydrological cycle. In this context, an Eddy-covariance flux station was installed on the Tazaghart plateau, a wide flat area located at 3850 m.a.s.l. in the High Atlas mountain of Morocco, allowing continuous acquisitions between September 2020 and January 2021, with a timestep of 30 minutes, in order to estimate evapotranspiration and sublimation processes. The observation period included three successive contrasted phases, namely bare soil in September, a period dominated by snowmelt in October after the first snowfall, and finally, after two other snowfall events, a period dominated with sublimation in December.

The preliminary data analyses, from September 2020 to January 2021, show a diurnal sublimation cycle with a peak in the early afternoon and the highest relative snow sublimation fluxes that occurred with subzero temperatures, low atmospheric humidity and high incoming radiation. The daily average rate of sublimation measured was 0.41 mm per day. Measured sublimation accounted for 42% and 40% of snow ablation, based on the energy and water balance respectively. The estimated percentages are comparable, which supports the reliable measurements and provides validation of the Eddy covariance method, showing the ability of the Eddy covariance technic to quantify the direct measurements of winter water loss due to the sublimation of snowpacks, especially in higher areas where measurements are relatively difficult and rare.