Thèse Reconstruction de l'Évolution des Glaciers de l'Himalaya Central Depuis 1970 et Imlications pour la Reconstruction des Fluctuations des Glaciers au Cours de l'Holocène H/F - 38

Établissement : Université Grenoble Alpes
École doctorale : STEP - Sciences de la Terre de l'Environnement et des Planètes
Laboratoire de recherche : Institut des Géosciences de l'Environnement (IGE)
Direction de la thèse : Fanny BRUN ORCID 6607000166070667
Début de la thèse : 2026-10-01
Date limite de candidature : 2026-04-19T23:59:59

Ce projet de thèse a pour objectif de reconstituer l'évolution de 40 glaciers de la région centrale de l'Himalaya depuis les années 1960 à l'aide d'observations par télédétection, de mesures in situ à long terme du bilan de masse, d'une méthode spécifique de réduction d'échelle des données de
réanalyse climatique et de la modélisation glaciaire à l'échelle mondiale. Le deuxième objectif de ce projet de doctorat est d'utiliser un modèle glaciaire global (OGGM) bien calibré pour simuler les trajectoires des glaciers au cours de l'Holocène à l'aide de simulations paléoclimatiques à grande échelle dédiées. Tous ces travaux portant sur le passé récent et lointain (Holocène) permettront de mieux comprendre le lien entre le changement climatique et l'évolution de chaque glacier
en tenant compte des conditions géomorphologiques des glaciers et du climat local, ce qui
rendra finalement les estimations de l'évolution future des glaciers plus fiables et spatialement cohérentes.

The western-central Himalaya (WCH ; India, Nepal and Bhutan) which can be subdivided in 4 climatic zones (Fig. 1) is home to around 17 000 glaciers which are sources of the 3 major rivers Brahmaputra, Ganga and Indus. These rivers are essential for water, agriculture and energy supply for hundreds of millions of people [IPCC, SROCC, 2019]. Over the recent decades some sectors of the region have experienced very hot summers (> 50°C for several days in large cities of India) and, like all mountain regions in the world, a large glacier retreat that has also caused major glacier lake outburst floods destroying villages [Immerzeel et al., 2020 ; Hugonnet et al., 2021 ; The GLAMBIE team, 2025]. Furthermore, glacier future evolution in this region is expected to decrease their ice volume by 25 to 60% by 2100 - with large spatial variability - depending on pathway of human greenhouse gases emission [Marzeion et al., 2020], and between 50 to 90% after long-term equilibrium (i.e. after many centuries ; Zekollary and Schuster et al., 2025).

WCH glaciers are influenced by two main climate systems: the westerlies and the Indian and
Eastern Summer Monsoons in the eastern part of the range. In recent decades, regional
glacier mass loss has been quantified but results highlight a large spatial heterogeneity
[Sakai et al., 2017 ; Brun et al., 2017], preventing a robust estimate of future changes and
associated risks for society. Indeed, the interplay between climatic (regional climate,
weather regimes, seasonal moisture, orographic effects...), geomorphological (debris
coverage, hypsometry of the watershed, presence of a terminal lake, etc.) and
environmental factors (vegetation, soil...) are still poorly understood [Brun et al., 2019]. A
robust analysis of their respective role in mass balance changes is missing so far as current
studies are based on an observational period that is too short to account for the glacier's
long-term history. Thus, glaciers that are very sensitive to climate change cannot be
distinguished from others whose behaviors are more controlled by geomorphological
conditions with a muted or delayed reaction to current climate change. Moreover, a more
accurate quantification of the anthropogenic and natural contribution to such glacier change
is needed. It is for example unknown whether the current glacier retreat is unprecedented
compared to that during warm periods of the Holocene (last 11 600 years), as recently
reported for some tropical glaciers [Gorin et al., 2024]. In addition, in situ observations of
glacier mass balance are sparse in the WCH, due to the difficult access and large size of the
glaciers, which questions the robustness of glacier model calibration. For all these reasons, it
is still difficult to estimate the future evolution of glaciers in the WCH, especially its spatial
variability.