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Twenty-first-century glacio-hydrological changes in the Himalayan headwater Beas River basin

Abstract. The Himalayan Mountains are the source region of one of the world's largest
supplies of freshwater. The changes in glacier melt may lead to droughts as
well as floods in the Himalayan basins, which are vulnerable to hydrological
changes. This study used an integrated glacio-hydrological model, the Glacier
and Snow Melt – WASMOD model (GSM-WASMOD), for hydrological projections
under 21st century climate change by two ensembles of four global climate models (GCMs) under two Representative Concentration
Pathways (RCP4.5 and RCP8.5) and
two bias-correction methods (i.e., the daily bias correction (DBC) and the
local intensity scaling (LOCI)) in
order to assess the future hydrological changes in the Himalayan Beas basin
up to Pandoh Dam (upper Beas basin). Besides, the glacier extent loss during
the 21st century was also investigated as part of the glacio-hydrological
modeling as an ensemble simulation. In addition, a high-resolution WRF
precipitation dataset suggested much heavier winter precipitation over the
high-altitude ungauged area, which was used for precipitation correction in
the study. The glacio-hydrological modeling shows that the glacier ablation
accounted for about 5 % of the annual total runoff during 1986–2004 in
this area. Under climate change, the temperature will increase by
1.8–2.8 ∘C at the middle of the century (2046–2065), and by
2.3–5.4 ∘C until the end of the century (2080–2099). It is very
likely that the upper Beas basin will get warmer and wetter compared to the
historical period. In this study, the glacier extent in the upper Beas basin
is projected to decrease over the range of 63 %–87 % by the middle
of the century and 89 %–100 % at the end of the century compared to
the glacier extent in 2005. This loss in glacier area will in general result
in a reduction in glacier discharge in the future, while the future
streamflow is most likely to have a slight increase because of the increase
in both precipitation and temperature under all the scenarios. However, there
is widespread uncertainty regarding the changes in total discharge in the
future, including the seasonality and magnitude. In general, the largest
increase in river total discharge also has the largest spread. The
uncertainty in future hydrological change is not only from GCMs, but also
from the bias-correction methods and hydrological modeling. A decrease in
discharge is found in July from DBC, while it is opposite for LOCI. Besides,
there is a decrease in evaporation in September from DBC, which cannot be
seen from LOCI. The study helps to understand the hydrological impacts of
climate change in northern India and contributes to stakeholder and
policymaker engagement in the management of future water resources in
northern India.
