Abstract
Abstract. In the Nepalese Himalayas, the complex topography, occurrence of debris covered glaciers, and limited data availability creates substantial difficulties for modelling glacier melt. The proper recognition of melt processes governs the accurate estimation of melt water from glacier dominated systems, even in the presence of debris-covered glaciers. This paper presents a glacier melt model developed for the Lirung sub-basin of Langtang valley, which has both a clean glacier area, 5.86 km2, and a debris-covered glacier area, 1.13 km2. We use a temperature index approach to estimate sub-daily melt water discharge for a two week period at the end of monsoon, and the melt factor is varied according to the aspect and distributed to each grid processed from the digital elevation model. The model uses easily available data and simple extrapolation techniques capable of generating melt with limited data. The result obtained from this method provides accurate estimate with an R2 value of 0.89, bias of 0.9% and Nash-Sutcliffe efficiency of 0.86, and suitable in Himalaya where data availability is major issue.
Highlights
Debris-covered glaciers are common features of the Himalaya and mountain regions throughout the world
The R2 value is >0.80 but there is a clear difference in the Nash-Sutcliffe efficiency (NSE; Nash and Sutcliffe, 1970) as well as mean bias
The aspect and elevation modified temperature index method has the greatest accuracy of the three melt modelling methods, with R2 = 0.89, a small mean bias (2.4%) and the highest NSE (0.86)
Summary
Debris-covered glaciers are common features of the Himalaya and mountain regions throughout the world. Numerous studies have attempted to model the melt water discharge using a positive degree day approach (Kayastha et al, 2000a, 2005). The energy balance approach best describes the effects of debris cover on melt totals (Hock, 1999, 2003), input data availability is a significant constraint. We estimate melt from the debris-covered Lirung Glacier, and compare modelled and observed discharge for a small Himalayan catchment.
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