Work Package 3 - Assessment of snow accumulation over glaciers: more insights about spatial variability of precipitation at multiple scales (Resp: F. Brun – recruited at IRD in 2020)
Measuring solid precipitation at high elevation is challenging and needs specific devices like Geonor all-weather rain gauges that are impossible to deploy over ice covered areas. However, solid precipitation may be assessed using accumulation measurements on glaciers, combining different approaches. Here, we will combine field measurements and remote sensing tools to study the spatial variability of solid precipitation at local (glacier) and regional scales (Dudh Koshi basin). We will benefit from more than 10 years of point mass balance measurements collected on different glaciers monitored in the Everest region25 (Fig. 1) to assess precipitation at high elevation.
Spatial variability of snow accumulation at high altitude is one of the major knowledge gaps in the Himalayan glacio-hydrology. A first step is the assessment of the precipitation variability at the scale of a glacier. Over the recent years, some studies used Ground Penetrating Radar (GPR) measurements to capture the spatial distribution and annual variability of snow accumulation on some glaciers . For the first time in the Himalayas, we will perform GPR measurements on Mera Glacier in order to estimate the spatial distribution and annual variability in snow accumulation. Combined to several accumulation cores, needed to calibrate the radar echo depths and determine the snow density, the GPR allows to document both total snow accumulation and to resolve the spatial variability of accumulation at glacier scale. The GPR measurements will therefore inform us about: 1- the ability of the existing mass balance network to capture glacier-wide accumulation and 2- to assess the importance of spatial variability of accumulation at small scale. Tests conducted in the French Alps in springs 2018 and 2019 with the Mala GPR device equipped with a 250 MHz Antenna available at IGE gave promising results .
Accumulation measurements on Mera Glacier (GPR and snow pits), and recent progresses in melt modelling and estimates of sublimation , will pave the way to test inverse mass balance modelling techniques on Mera Glacier. Inverse mass balance modelling consists in inversely estimating the precipitation amounts based on estimates of the other components of surface mass balance12,13. However, this methodology was never tested against in-situ measurements, and Mera Glacier data offer this possibility. If good results are obtained, we will then be confident in applying a similar technique at much larger scale for all the glaciers in the Everest region, for which the glacier-wide mass balance for the period 2000-present is known from remote sensing observations20,21. We will use the valley-observed precipitation data in mass balance model simulations and the vertical precipitation gradients will be adjusted until the simulated mass balances match with observed mass balances. After this process, the inversely estimated precipitation will be compared with collected point-scale precipitation at glacier altitudes to validate this inverse model. This exercise will result in the spatial fields representing the altitudinal dependence of precipitation, which will be one of the bases for evaluation of climate models (WP4). These data will be freely distributed through ICIMOD data sharing platform and the GLACIOCLIM website. Further, the temperature measurements will allow us to develop the seasonal changes in snow/rain limit altitudes maps, as well as the spatio-temporal evolution of the temperature lapse rates.

Updated on 8 April 2022