Mass balance and runoff modelling of partially debris-covered Dokriani Glacier in monsoon-dominated Himalaya using ERA5 data since 1979

Abstract

Glacier-wide mass balance and catchment-wide runoff were reconstructed over 1979–2018 for Dokriani Glacier catchment in Garhwal Himalaya (India). A glacier mass balance-runoff model, including temperature-index, accumulation, and rain modules was used for the reconstruction using daily air-temperature and precipitation fields from ERA5 reanalysis products. The model was calibrated using 6 years of observed annual glacier-wide mass balances (1993–1995 and 1998–2000) and observed summer mean monthly runoff (1994, 1998–2000) data. Model validation was done using satellite-derived snow line altitudes and field-observed runoff (1997–1998). Modelled mass balance on Dokriani Glacier is moderate with annual loss of −0.25 ± 0.37 m w.e. a–1 over 1979–2018. The mean winter glacier-wide mass balance is 0.72 ± 0.05 m w.e. a–1 while mean summer glacier-wide mass balance is −0.97 ± 0.32 m w.e. a–1 over 1979–2018. The mean annual catchment-wide runoff is 1.56 ± 0.10 m3 s−1 over 1979–2018. Maximum runoff occurs during summer-monsoon months with a peak in August (6.04 ± 0.34 m3 s−1). Rainfall contributes the most to the total mean annual runoff with 44 ± 2% share, while snow melt and ice melt contribute 34 ± 1% and 22 ± 2%, respectively. The heterogeneous debris-cover distribution over lower ablation area (<5000 m a.s.l.) retards melting and protects the glacier. Modelled decadal mass balances suggest that Dokriani Glacier was close to steady-state conditions over 1989–1997 because of negative temperature anomalies and positive precipitation anomalies over this period. Mass balance and runoff are most sensitive to the threshold temperature for melt with sensitivities of 0.77 m w.e. a–1 °C−1 and −0.20 m3 s−1 oC–1, respectively. © 2020