Snow dynamics in the Himalaya

Abstract

The word Himalaya stems from Sanskrit, and literally translates as the abode of snow. This is illustrative of the importance of snow in this mountain range. The Himalaya is the highest mountain range on earth. Large areas are seasonally or even permanently covered in snow. The Himalaya is often referred to as the water tower of Asia, mostly because large amounts of fresh water are stored in snow and glacier ice. These frozen water towers act as a seasonal storage of water and provide a reliable and steady supply of meltwater to millions of people who live downstream in particular during droughts. In the last decade, glacier research in the Himalaya has really taken off and a plethora of studies has been published quantifying mass balances and glacier hydrological processes using direct observations, remote sensing or modelling. However, Himalaya snow research did not evolve as quickly and was mainly constrained to remote sensing studies focusing on snow cover trends. Since the snow covered area in the Himalaya is considerably larger than the glacier area, it is safe to assume that snowmelt plays a key role in the Himalayan water cycle, possibly, even more important than glacier melt. There is therefore a very large knowledge gap in data driven snow studies in the region that focus on critical processes in the energy and mass balance of the snowpack in the Himalaya. In this thesis, I contribute to closing this knowledge gap by using a combination of unique snow observations high in the Himalaya, remote sensing and modelling to study a number of those key processes. In particular, I focus on quantifying the snow water equivalent, the cold content, sublimation and refreezing of meltwater in the snowpack. This thesis shows the critical role that sublimation, refreezing of snow meltwater and snowpack cold content dynamics play in the energy and mass balance of the snowpack at high altitude. Future snow and hydrological studies should include these essential processes. So far, the vast majority of models applied in the region use the air temperature as a proxy for melt. However, in my thesis I showed that the reality is much more complex and that using the air temperature does not capture those processes which control the energy and mass balance of the snowpack. Future hydrological model studies in the Himalaya should attempt to simulate the full energy balance and mass balance, despite the fact that a lot of data is required. By setting up a number of well instrumented snow observatories, combined with smart downscaling of reanalysis data and high-resolution remote sensing, most of these data challenges can be overcome. Admittedly it is a large investment, but it is the only way forward to improve the hydrological forecasts and projections in this complex environment.