Fig 1.
Map of the study area showing the outlets of the basins and the gauging stations used for calibration and validation of the model. Source of the background basemap imagery and the political borders displayed in the inlet of the figure is www.naturalearthdata.com.
Fig 2.
Climate of the Upper Indus, Ganges, and Brahmaputra basins.
Maps of the upstream domains of the Indus, Ganges, and Brahmaputra showing the annual precipitation (a), the average air temperature (b), the winter precipitation (c), the monsoon precipitation (d), and the precipitation extremes (P95 (e) and P99 (f)) for the reference period. Abbreviations: DJF = December, January, February, JJAS = June., July, August, September, P95 = 95th percentile of daily precipitation sums, P99 = 99th percentile of daily precipitation sums. Source of the maps is a reference climate dataset [45].
Table 1.
Parameters and their ranges used for the calibration.
Table 2.
Simulated and observed mean snow cover and glacier mass balance.
Abbreviations: w.e. = water equivalent.
Table 3.
Calibrated model parameters and their values.
Table 4.
Model performance ratings in terms of NSE and PBIAS that were calculated on daily basis for the calibration and validation periods, separately.
PBIAS Q90 represents the percent bias for the 90-percentile discharge level for the calibration and validation periods. Abbreviations: C = Calibration, V = Validation.
Fig 3.
Annual catchment-averages of most important water balance components and observed discharge at 6 gauging stations used for calibration and validation.
Abbreviations: P = precipitation, ET = actual evapotranspiration, SU = actual sublimation, Q observed = observed discharge, Q baseflow = baseflow, Q glacier = glacier melt, Q snow = snow melt, and Q rain = rainfall runoff.
Table 5.
Basin-averaged values for a range of climate variables for the reference period and the relative (precipitation) and absolute (temperature) changes at the end of the 21st century as projected by each of the downscaled GCM runs used in this study.
Abbreviations: P = mean annual precipitation sum, P90, P95, and P99: 90th, 95th, 99th percentiles of daily precipitation sums, RX5 = maximum 5-day precipitation amount, T = annual mean temperature, and HWFI = warm spell days index.
Fig 4.
Maps showing the changes in P95 and the HWFI index for RCP4.5 and RCP8.5. Contour lines denote the ensemble range of projections.
Fig 5.
Present and future annual maximum series (AMS).
The mean AMS for the period 1981–2100 under RCP4.5 (red) and RCP8.5 (blue). The AMS are given for the Upper Brahmaputra and Hunza basins. The colored band represents the standard deviation resulting from forcing the hydrological model with the different climate models.
Table 6.
Changes in the mean discharge, 99th percentile of daily discharge values (Q99), and the discharge levels of events with return periods of 5, 25 and 50 years at the outlets of the UIB, UGB, UBB, and the upstream catchments (Hunza, Marshyangdi, and Sankosh) under present (1981–2010), near future (2035–2064), and far future (2071–2100) RCP4.5 and RCP8.5 climate conditions.
The values between the parentheses represent the standard deviation.
Fig 6.
Relative changes in 50-year return period discharge level.
Maps showing the mean relative changes (left) in 50-year return period discharge levels and their standard deviations (right) at the end of 21st century (2071–2100) under RCP4.5 (upper row) and RCP8.5 (lower row) scenarios.
Fig 7.
Reference and future flow duration curves (FDCs).
The FDCs of the reference (black lines) and far future period (dashed lines) at the outlets of the Upper Brahmaputra and Hunza basins. The FDCs represent mean flow conditions under RCP4.5 (red) and RCP8.5 (blue). The colored band represents the standard deviation resulting from forcing the hydrological model with the different climate models.