Bilan d'énergie ponctuel et saisonnalité hydrologique du glacier Zongo (Bolivie)

¹ LGGE
² ORSTOM

Abstract

The proglacial stream escaping from Zongo Glacier (Bolivia, 16 °S) shows high discharges during the wet season (October - March.) and low discharges during the dry season (May - August), although neither net radiation, nor air temperature are variable enough to explain this large seasonality. Then, a detailed energy balance study has been carried out on this tropical glacier (2.1 km²) since March 1996, at the altitude of the mean equilibrium line (5 150 m a.s.l.). Each component of the energy balance (net radiation, sensible and latent heat fluxes, heat transfer into the ice and heat supplied by precipitation) are derived separately to know which energy flux(es) is(are) responsible for the high seasonality of the proglacial stream discharge. Net radiation and turbulent fluxes dominate the surface energy balance: net radiation is obviously the main source of energy at the glacier surface but quantitatively, this energy input does not change a lot from season ta season. Sensible heat flux remains small throughout the year, and does not show any seasonality either. On the contrary, latent heat flux is very variable with seasons. During the dry season, at the glacier surface, the energy input as net radiation is almost entirely consumed by the high sublimation (penitents grow at the surface), and therefore, melting is reduced and discharge is low. During the wet season, the high humidity of the surface layer stops the sublimation, and the energy input is used for melting, leading to high discharge.