Quantification of different flow components in a high-altitude glacierized catchment (Dudh Koshi, Himalaya): some cryospheric-related issues

Abstract

Abstract. In a context of climate change and water demand growth, understanding the origin of water flows in the Himalayas is a key issue for assessing the current and future water resource availability and planning the future uses of water in downstream regions. Two of the main issues in the hydrology of high-altitude glacierized catchments are (i) the limited representation of cryospheric processes controlling the evolution of ice and snow in distributed hydrological models and (ii) the difficulty in defining and quantifying the hydrological contributions to the river outflow. This study estimates the relative contribution of rainfall, glaciers, and snowmelt to the Khumbu River streamflow (Upper Dudh Koshi, Nepal, 146 km2, 43 % glacierized, elevation range from 4260 to 8848 m a.s.l.) as well as the seasonal, daily, and sub-daily variability during the period 2012–2015 by using the DHSVM-GDM (Distributed Hydrological Soil Vegetation Model – Glaciers Dynamics Model) physically based glacio-hydrological model. The impact of different snow and glacier parameterizations was tested by modifying the snow albedo parameterization, adding an avalanche module, adding a reduction factor for the melt of debris-covered glaciers, and adding a conceptual englacial storage. The representation of snow, glacier, and hydrological processes was evaluated using three types of data (MODIS satellite images, glacier mass balances, and in situ discharge measurements). The relative flow components were estimated using two different definitions based on the water inputs and contributing areas. The simulated hydrological contributions differ not only depending on the used models and implemented processes, but also on different definitions of the estimated flow components. In the presented case study, ice melt and snowmelt contribute each more than 40 % to the annual water inputs and 69 % of the annual stream flow originates from glacierized areas. The analysis of the seasonal contributions highlights that ice melt and snowmelt as well as rain contribute to monsoon flows in similar proportions and that winter outflow is mainly controlled by the release from the englacial water storage. The choice of a given parametrization for snow and glacier processes, as well as their relative parameter values, has a significant impact on the simulated water balance: for instance, the different tested parameterizations led to ice melt contributions ranging from 42 % to 54 %. The sensitivity of the model to the glacier inventory was also tested, demonstrating that the uncertainty related to the glacierized surface leads to an uncertainty of 20 % for the simulated ice melt component.

Glacio‐hydrological model calibration and evaluation

“…A few models accumulate snow at specific locations in the catchment due to avalanches or wind redistribution of snow (e.g., Huss et al, 2008;Mimeau et al, 2019;Ragettli & Pellicciotti, 2012). In other models a simpler approach is used, for example, Duethmann et al (2015) distributed snow to the rest of the catchment if SWE was above 3 m and Tarasova et al (2016) drifted the snow that has not melted during the ablation period one elevation band lower in the following winter.…”

“…Beamer et al (2016), Loukas et al (2002), Naz et al (2014), Soncini et al (2015), and Jost et al (2012) all used SWE data for validation (point scale). The few studies that did not include a formal calibration in the modeling process (uncalibrated models) conducted quite an extensive validation procedure (e.g., Milchmayr et al, 2008;Mimeau et al, 2019;Willis et al, 2002). Lutz et al (2016) and Wang et al (2018) used independent streamflow data from stations inside the catchment.…”

Biofuel Burning Influences Refractory Black Carbon Concentrations in Seasonal Snow at Lower Elevations of the Dudh Koshi River Basin of Nepal

“…(Armstrong et al, 2018). However, other recently published studies also show that local basin hypsometry plays an important role in high elevation meltwater contributions (Mimeau et al, 2019). Therefore, contributions of snow on land, snow on ice, and exposed glacier ice may vary from basin to basin at high elevations.…”

Field Study of Mass Balance, and Hydrology of the West Khangri Nup Glacier (Khumbu, Everest)

“…We used the so-obtained values of ρ n to estimate new snow density here. During the period 2010-2014, some field surveys were performed in fulfillment of the SHARE-Paprika and SHARE-Dudh Koshi River projects upon the Khangri and Khumbu glacier [8,21,67], including on the West Khangri Nup. Ice melt and snow melt/depth were measured at seven positions, using plastic and bamboo sticks (hereon, ice/snow stakes).…”

“…Mimeau et al [67] also studied hydrological flow components in the Dudh Koshi river closed at Pheriche. During 2012-2015, they estimated an ice flow contribution ranging from 41% to 71% (average 58%, Figure 7 in [67]), and snow contribution ranging from 23% to 47% (average 31%, Figure 7 in [67]); however, this was dependent largely on the year (2012-2013, 2013-2014, 2014-2015), ice/snow melt parameterization, uncertainly estimated ice/snow-covered areas, and different definitions of the flow components.…”