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

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 m(3) s(-1) over 1979-2018. Maximum runoff occurs during summer-monsoon months with a peak in August (6.04 +/- 0.34 m(3) 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) degrees C-1 and -0.20 m(3) s(-1) degrees C-1, respectively.