Key Messages
• The Himalayas and the Tibetan Plateau have experienced
substantial warming during the twentieth century. The
warming trend has been particularly pronounced over the
Hindu Kush Himalaya (HKH) which is the largest area of
permanent ice cover outside the North and South Poles.
• The annual mean surface-air-temperature in the HKH
increased at a rate of about 0.1 °C per decade during
1901–2014, with a faster rate of warming of about 0.2 °C
per decade during 1951–2014, which is attributable to
anthropogenic climate change (High confidence). Additionally, high elevations (> 4000 m) of the Tibetan Plateau have experienced stronger warming, as high as 0.5 °
C per decade, which is commonly referred to as
elevation-dependent warming (EDW).
• Several areas in the HKH have exhibited declining trends
in snowfall and retreating glaciers during the recent
decades. Parts of the high-elevation Karakoram Himalayas have, in contrast, experienced increased wintertime
precipitation in association with enhanced amplitude
variations of synoptic western disturbances (Medium
confidence).
• Future climate projections under various CMIP5 scenarios suggest warming of the HKH region in the range of
2.6–4.6 °C by the end of the twenty-first century. While
future projections indicate significant decrease of snowfall in several regions of the HKH, high-elevation locations (> 4000 m) in the Karakoram Himalayas are
projected to experience an increase in annual precipitation
during the twenty-first century.
11.1 Introduction
The name “Himalaya” means “the abode of snow” in Sanskrit. The continental drift theory suggests that the Himalayas were formed about 50 million years ago when the
Indian plate collided with the Eurasian plate (Kious and
Tilling 1996). The large spatial extent of the Himalayas
(Fig. 11.1) spans across eight countries of the Asian continent and is the source of ten major river systems (Sharma
et al. 2019, HIMAP) providing water for drinking, irrigation
and power for over 1.3 billion people in Asia—which is
nearly 20% of the world’s population (e.g. Bookhagen and
Burbank 2006; Rashul 2014). The Himalayan mountain
range is the world’s tallest and is notably the home to 10 of
the 14 world’s highest peaks, while the Karakoram and the
Hindu Kush are generally viewed as separate ranges in the
literature (Godin et al. 1999). The area that encompasses the
Hindu Kush Himalaya (HKH) mountain range and the
Tibetan Plateau (TP) is popularly known as the “Third Pole”
as it contains the largest reserve of freshwater outside the
north and south poles. The meltwater generated from the
Himalayan glaciers supplies the rivers and streams of the
region, including the Indus, Ganges and Brahmaputra river
systems of India. These rivers collectively provide about
50% of the country’s total utilisable surface water resources
(Srivastava and Misra 2012). Scientific evidence also shows
that most glaciers in the HKH region are subjected to loss in
volume and mass under the propensity of rising temperatures
due to climate change (Kulkarni and Karyakarte 2014;
ICIMOD 2007, 2011; Armstrong 2011; Wester et al. 2019;
IPCC SROC 2019). Yet, a clear understanding and quantification of its consequences in these mountain ranges
remain challenging.
The climate of the HKH is characterised by
tropical/subtropical climatic conditions from the foothill
region of the mountains to permanent ice and snow-covered
peaks at higher altitudes (Pant et al. 2018). Flora and fauna
of the Himalayas vary with climate, rainfall, altitude and
soils. The amount of annual rainfall increases from west to
east along the southern front of the range. Further, the
Himalaya is delineated by different climatic sub-zones due to
diverse geographical variability, which is closely linked to
topographical distribution of the region (Bookhagen and
Burbank 2006). The annual cycle of temperature and precipitation differs substantially in these different zones. Seasonal variations in the mean climate of HKH are closely tied
to the seasonal cycle of the regional atmospheric processes
(Box 11.1).
The valleys experience mean summer temperatures
between 15 and 25 °C and much colder in winter. Regions
with elevations above 4500 m experience severe winter,
with temperatures far below freezing point and precipitation
in the form of snow, e.g. the Karakoram range of the
Himalayas experiences an average maximum temperature of
about 20 °C during the summer, and average minimum
temperature goes below −3 °C in February (Hasson et al.
2014; Kapnick et al. 2014). The north-western peaks of
Himalayas typically experience dry conditions, with surface
temperatures ranging between 3 and 35 °C in summer and
−20 and −35 °C in winter together with heavy snowfall.
The climate of the HKH has been experiencing significant
temperature changes since twentieth century where the
warming trend during the first (second) half of the twentieth
century was about 0.10 °C (0.16 °C) per decade, which later
doubled to 0.32 °C per decade from the beginning of the
twenty-first century (Yan and Liu 2014). The warming rate is
reported to be more substantial in winter as compared to other
seasons in most parts of the HKH region (Bhutiyani et al.
2007; Shrestha et al., 2010). Studies by Dimri and Dash
(2012), Negi et al. (2018), etc., also confirm that most of the
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T. P. Sabin et al.
• The Himalayas and the Tibetan Plateau have experienced
substantial warming during the twentieth century. The
warming trend has been particularly pronounced over the
Hindu Kush Himalaya (HKH) which is the largest area of
permanent ice cover outside the North and South Poles.
• The annual mean surface-air-temperature in the HKH
increased at a rate of about 0.1 °C per decade during
1901–2014, with a faster rate of warming of about 0.2 °C
per decade during 1951–2014, which is attributable to
anthropogenic climate change (High confidence). Additionally, high elevations (> 4000 m) of the Tibetan Plateau have experienced stronger warming, as high as 0.5 °
C per decade, which is commonly referred to as
elevation-dependent warming (EDW).
• Several areas in the HKH have exhibited declining trends
in snowfall and retreating glaciers during the recent
decades. Parts of the high-elevation Karakoram Himalayas have, in contrast, experienced increased wintertime
precipitation in association with enhanced amplitude
variations of synoptic western disturbances (Medium
confidence).
• Future climate projections under various CMIP5 scenarios suggest warming of the HKH region in the range of
2.6–4.6 °C by the end of the twenty-first century. While
future projections indicate significant decrease of snowfall in several regions of the HKH, high-elevation locations (> 4000 m) in the Karakoram Himalayas are
projected to experience an increase in annual precipitation
during the twenty-first century.
11.1 Introduction
The name “Himalaya” means “the abode of snow” in Sanskrit. The continental drift theory suggests that the Himalayas were formed about 50 million years ago when the
Indian plate collided with the Eurasian plate (Kious and
Tilling 1996). The large spatial extent of the Himalayas
(Fig. 11.1) spans across eight countries of the Asian continent and is the source of ten major river systems (Sharma
et al. 2019, HIMAP) providing water for drinking, irrigation
and power for over 1.3 billion people in Asia—which is
nearly 20% of the world’s population (e.g. Bookhagen and
Burbank 2006; Rashul 2014). The Himalayan mountain
range is the world’s tallest and is notably the home to 10 of
the 14 world’s highest peaks, while the Karakoram and the
Hindu Kush are generally viewed as separate ranges in the
literature (Godin et al. 1999). The area that encompasses the
Hindu Kush Himalaya (HKH) mountain range and the
Tibetan Plateau (TP) is popularly known as the “Third Pole”
as it contains the largest reserve of freshwater outside the
north and south poles. The meltwater generated from the
Himalayan glaciers supplies the rivers and streams of the
region, including the Indus, Ganges and Brahmaputra river
systems of India. These rivers collectively provide about
50% of the country’s total utilisable surface water resources
(Srivastava and Misra 2012). Scientific evidence also shows
that most glaciers in the HKH region are subjected to loss in
volume and mass under the propensity of rising temperatures
due to climate change (Kulkarni and Karyakarte 2014;
ICIMOD 2007, 2011; Armstrong 2011; Wester et al. 2019;
IPCC SROC 2019). Yet, a clear understanding and quantification of its consequences in these mountain ranges
remain challenging.
The climate of the HKH is characterised by
tropical/subtropical climatic conditions from the foothill
region of the mountains to permanent ice and snow-covered
peaks at higher altitudes (Pant et al. 2018). Flora and fauna
of the Himalayas vary with climate, rainfall, altitude and
soils. The amount of annual rainfall increases from west to
east along the southern front of the range. Further, the
Himalaya is delineated by different climatic sub-zones due to
diverse geographical variability, which is closely linked to
topographical distribution of the region (Bookhagen and
Burbank 2006). The annual cycle of temperature and precipitation differs substantially in these different zones. Seasonal variations in the mean climate of HKH are closely tied
to the seasonal cycle of the regional atmospheric processes
(Box 11.1).
The valleys experience mean summer temperatures
between 15 and 25 °C and much colder in winter. Regions
with elevations above 4500 m experience severe winter,
with temperatures far below freezing point and precipitation
in the form of snow, e.g. the Karakoram range of the
Himalayas experiences an average maximum temperature of
about 20 °C during the summer, and average minimum
temperature goes below −3 °C in February (Hasson et al.
2014; Kapnick et al. 2014). The north-western peaks of
Himalayas typically experience dry conditions, with surface
temperatures ranging between 3 and 35 °C in summer and
−20 and −35 °C in winter together with heavy snowfall.
The climate of the HKH has been experiencing significant
temperature changes since twentieth century where the
warming trend during the first (second) half of the twentieth
century was about 0.10 °C (0.16 °C) per decade, which later
doubled to 0.32 °C per decade from the beginning of the
twenty-first century (Yan and Liu 2014). The warming rate is
reported to be more substantial in winter as compared to other
seasons in most parts of the HKH region (Bhutiyani et al.
2007; Shrestha et al., 2010). Studies by Dimri and Dash
(2012), Negi et al. (2018), etc., also confirm that most of the
208
T. P. Sabin et al.