Browsing by Autor "Walter W. Immerzeel"

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Energy balance analysis of a tropical glacier in the Andes and identification of key meteorological variables for empirical melt estimates
(Cambridge University Press, 2025) Yoshihiro ASAOKA; Genki Saito; Takeshi Yamazaki; Edson Ramírez; Walter W. Immerzeel
Abstract This study investigated surface energy fluxes of the Huayna-Potosí Glacier in Bolivia to validate existing empirical melt estimates, including degree-day models and enhanced temperature-index models. A multilayer energy balance model of the snowpack was employed to estimate melt energy and analyze its correlation with meteorological variables. The energy balance analysis revealed that melt energy peaked in October and November, the period corresponding to the progressive development toward the core wet season. Most of the net radiation was consumed by the conductive heat flux into the snowpack or glacier ice, contributing to surface temperature increases. The remaining energy was used for melt. An analysis of diurnal variation indicated that atmospheric longwave radiation suppresses melt during the dry season while driving melt during the wet season. Variables such as specific humidity and relative humidity, which are related to atmospheric longwave radiation, emerged as primary controlling factors after solar radiation in estimating melt based on meteorological variables. This study highlights that a combination of solar radiation and specific humidity outperforms existing empirical melt models that depend exclusively on temperature or a combination of temperature and solar radiation.
Importance and vulnerability of the world’s water towers
(Nature Portfolio, 2019) Walter W. Immerzeel; Arthur Lutz; Marcos Andrade; Alexis A. Bahl; Hester Biemans; Tobias Bolch; S. Hyde; Steven P. Brumby; Bethan J. Davies; Aurora C. Elmore
Reduced melt on debris-covered glaciers: investigations from Changri NupGlacier, Nepal
(Copernicus Publications, 2016) Christian Vincent; Patrick Wagnon; J. M. Shea; Walter W. Immerzeel; Philip Kraaijenbrink; Dibas Shrestha; Álvaro Soruco; Yves Arnaud; Fanny Brun; Étienne Berthier
Abstract. Approximately 25 % of the glacierized area in the Everest region is covered by debris, yet the surface mass balance of debris-covered portions of these glaciers has not been measured directly. In this study, ground-based measurements of surface elevation and ice depth are combined with terrestrial photogrammetry, unmanned aerial vehicle (UAV) and satellite elevation models to derive the surface mass balance of the debris-covered tongue of Changri Nup Glacier, located in the Everest region. Over the debris-covered tongue, the mean elevation change between 2011 and 2015 is −0.93 m year−1 or −0.84 m water equivalent per year (w.e. a−1). The mean emergence velocity over this region, estimated from the total ice flux through a cross section immediately above the debris-covered zone, is +0.37 m w.e. a−1. The debris-covered portion of the glacier thus has an area-averaged mass balance of −1.21 ± 0.2 m w.e. a−1 between 5240 and 5525 m above sea level (m a.s.l.). Surface mass balances observed on nearby debris-free glaciers suggest that the ablation is strongly reduced (by ca. 1.8 m w.e. a−1) by the debris cover. The insulating effect of the debris cover has a larger effect on total mass loss than the enhanced ice ablation due to supraglacial ponds and exposed ice cliffs. This finding contradicts earlier geodetic studies and should be considered for modelling the future evolution of debris-covered glaciers.