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1 Introduction
The main rivers in India such as the Ganges, the Indus, the Sutlej and the Brahmaputra
originate from the Himalayan glaciers. These rivers are the life lines of a large population residing in India. Precipitation in the form of snow over the Himalaya helps
in glacier sustenance. Snow and ice melt in the high Himalaya influence the water
availability downstream in the major river basins especially in the summer. Snow
and ice contributions to river stream flow depend on the year-to year variations of
snowfall and snowmelt rate. Tiwari et al. (2016a) have examined large scale interannual variability in snowfall and snow accumulation in the western Himalaya.
Because of large heterogeneity in topography, different part of Himalaya receive
different amount of snowfall or rainfall. Bookhagen and Burbank (2010) have found
that the Indian summer monsoon is responsible for more than 80% of annual rainfall
in the central Himalaya and Tibetan plateau, eastern and western syntax receive
only about 50% of annual rainfall during summer season. During winter seasons,
the western Himalayan part receives more snowfall than any other region in the
Himalaya. The winter precipitation over the Himalaya shows considerable interannual variability mainly due to large variability in the frequency of western disturbances (WDs) during this season. The frequency and amplitude of these westerly
systems in a given season decides if that season will experience above normal or
below normal precipitation (Kar and Rana 2014). Influence of large-scale climate
forcing such as El Nino-Southern Oscillation, Arctic oscillation and North Atlantic
oscillations on the winter-time circulation and precipitation anomalies over the
Himalaya have been studied (Yadav et al. 2009; Kar and Rana 2014).
The coupled general circulation models (GCMs) or atmosphere-only GCMs
(AGCMs) are used to generate monthly to seasonal scale predictions. However, they
are unable to represent various regional scale processes because of their coarser
resolution. Tiwari et al. (2014) examined the skill of precipitation predictions from
several GCMs over north India during winter season and found that the coarse resolution GCMs have difficulty in predicting rainfall amount especially over the region
with sharp gradient in orography. Therefore, dynamic downscaling using highresolution regional models is necessary to understand the climate over such regions.
Complex topography and scarcity of observed data over the Himalaya is a serious
challenge for the modelling community to model and to predict the weather and
climate over this region even using regional models. Dimri (2014) has examined
downscaled output of regional climate models over the Siachen glaciers in the western Himalaya and found that these products need further tuning in order to make
those useful for basin-scale hydrological and glaciological studies. Sanjay et al.
(2017) used RCMs in the Coordinated Regional climate Downscaling Experiment
(CORDEX) South Asia framework to downscale GCM products under the Coupled
Model Intercomparison Project phase 5 (CMIP5). They have investigated the future
projections in seasonal mean near surface air temperature and precipitation over the
Hindu Kush Himalayan (HKH) Region. Due to lack of our understanding of complex precipitation processes (snowfall and rainfall) over the region with high
S. C. Kar et al.
1 Introduction
The main rivers in India such as the Ganges, the Indus, the Sutlej and the Brahmaputra
originate from the Himalayan glaciers. These rivers are the life lines of a large population residing in India. Precipitation in the form of snow over the Himalaya helps
in glacier sustenance. Snow and ice melt in the high Himalaya influence the water
availability downstream in the major river basins especially in the summer. Snow
and ice contributions to river stream flow depend on the year-to year variations of
snowfall and snowmelt rate. Tiwari et al. (2016a) have examined large scale interannual variability in snowfall and snow accumulation in the western Himalaya.
Because of large heterogeneity in topography, different part of Himalaya receive
different amount of snowfall or rainfall. Bookhagen and Burbank (2010) have found
that the Indian summer monsoon is responsible for more than 80% of annual rainfall
in the central Himalaya and Tibetan plateau, eastern and western syntax receive
only about 50% of annual rainfall during summer season. During winter seasons,
the western Himalayan part receives more snowfall than any other region in the
Himalaya. The winter precipitation over the Himalaya shows considerable interannual variability mainly due to large variability in the frequency of western disturbances (WDs) during this season. The frequency and amplitude of these westerly
systems in a given season decides if that season will experience above normal or
below normal precipitation (Kar and Rana 2014). Influence of large-scale climate
forcing such as El Nino-Southern Oscillation, Arctic oscillation and North Atlantic
oscillations on the winter-time circulation and precipitation anomalies over the
Himalaya have been studied (Yadav et al. 2009; Kar and Rana 2014).
The coupled general circulation models (GCMs) or atmosphere-only GCMs
(AGCMs) are used to generate monthly to seasonal scale predictions. However, they
are unable to represent various regional scale processes because of their coarser
resolution. Tiwari et al. (2014) examined the skill of precipitation predictions from
several GCMs over north India during winter season and found that the coarse resolution GCMs have difficulty in predicting rainfall amount especially over the region
with sharp gradient in orography. Therefore, dynamic downscaling using highresolution regional models is necessary to understand the climate over such regions.
Complex topography and scarcity of observed data over the Himalaya is a serious
challenge for the modelling community to model and to predict the weather and
climate over this region even using regional models. Dimri (2014) has examined
downscaled output of regional climate models over the Siachen glaciers in the western Himalaya and found that these products need further tuning in order to make
those useful for basin-scale hydrological and glaciological studies. Sanjay et al.
(2017) used RCMs in the Coordinated Regional climate Downscaling Experiment
(CORDEX) South Asia framework to downscale GCM products under the Coupled
Model Intercomparison Project phase 5 (CMIP5). They have investigated the future
projections in seasonal mean near surface air temperature and precipitation over the
Hindu Kush Himalayan (HKH) Region. Due to lack of our understanding of complex precipitation processes (snowfall and rainfall) over the region with high
S. C. Kar et al.