Glacio-hydrological modelling of partially debris-covered Dokriani Glacier in monsoon-dominated Garhwal Himalaya (India)

Glacier-wide mass balances and catchment-wide runoffs are reconstructed over 1979-2018 for Dokriani Glacier catchment in the Garhwal Himalaya (India). A glacio-hydrological model including temperature-index, accumulation, rain and evapotranspiration modules is used for the reconstruction using daily air-temperature and precipitation fields from ERA5 data. Model is 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. Modelled mass wastage on Dokriani Glacier is moderate with annual loss of −0.28±0.38 m w.e. a^–1 over 1979-2018. The mean winter glacier-wide mass balance is 0.62±0.38 m w.e. a^–1 while mean summer glacier-wide mass balance is −0.91±0.38 m w.e. a^–1 over 1979-2018. The mean annual catchment-wide runoff is 1.38±0.11 m³ s^–1 over 1979-2018. Maximum runoff is produced during summer-monsoon months with a peak in August (5.35 m³ s⁻¹). Rainfall contributes the maximum to the total mean annual runoff with 44% share while snow melt and ice melt contribute 35% and 22%, respectively. The loss through evapotranspiration is only around 2% of the total runoff. The heterogeneous debris-cover distribution over lower ablation area (<5000 m a.s.l.) protects the glacier for higher melting. Decadal mass balances suggest that Dokriani Glacier was close to steady-state conditions over 1989-1997 because of negative temperature anomaly and positive precipitation anomaly over this period. Mass balance and runoff are the most sensitive for threshold temperature for melt with sensitivities of −0.71 m w.e. a^–1oC^–1 and 0.18 m³ s^{–1 o}C^–1, respectively.