Glaciohydrology of Himalaya-Karakoram: functioning of glacierized catchments in monsoon and alpine climatic regimes

Abstract

The Himalaya-Karakoram (HK) region is one of the most heavily glacierized and vulnerable mountainous regions on earth that supplies a significant amount of water to the Indus, Ganga, and Brahmaputra River basins. The field-based studies are limited in the HK hence remote sensing and glaciohydrological modelling provide an alternative solution to investigate the glacier mass balance and runoff evolution under changing climate. In the present thesis, a detailed review about the glaciohydrology of the HK region is developed that discusses the present status and recent advancements in the HK cryosphere, and highlights the critical knowledge gaps that severely affect the modelled contributions of different runoff components. Further, two highly glacierized Himalayan catchments —Dokriani Bamak (DBG) in the monsoon regime and Chhota Shigri (CSG) in the Alpine regime—were selected for the detailed glacier runoff-climate investigations since 1950 using remote sensing methods, Temperature-index (T-index) glaciohydrological, and glacier-wide mass and Surface Energy Balance (SEB) models. T-index mass balance modelling on DBG and CSG showed decadal positive mass balances over 1950–1980s followed by a limited wastage over 1980–2000, and an accelerated mass wastage post-2000, in agreement with satellite-derived limited areal and snout changes up to 1990s, and then accelerated rates post-2000. In line, glacier-wide mass and SEB modelling also suggest a moderate mass wastage on both the glaciers since 1979 that is dominantly controlled by net shortwave radiation followed by longwave net radiation, latent and sensible heat flux. The long-term glaciohydrological modelling on both DBG and CSG catchments suggests that the higher catchment-wide runoffs correspond to more negative mass balances, and vice versa, that contrasts with the previously suggested mass balance-runoff relationship on DBG catchment. Detailed analysis also indicates that the hydrology of the DBG catchment in the monsoon regime is mainly dominated by the summer precipitation, while in CSG catchment in the Alpine regime, the hydrology is mainly controlled by the glacier-wide annual mass balance.