section provides a brief overview of the mean climate of the
Indian subcontinent and sets the context for understanding
the key aspects of climate change in the region.
1.1.1 Setting the Regional Context
The distinct topographical and geographical features of the
Indian subcontinent endow the region with widely varying climatic zones ranging from the arid Thar desert in the north-west,
Himalayan tundra in the north, humid areas in the southwest,
central and northeastern parts, together with diverse microclimatic areas that spread across the vast subcontinent. A dominant
feature of the regional climate is the Indian Summer Monsoon
(ISM), which is characterized by pronounced seasonal migrations of the tropical rain belts associated with the Inter-tropical
Convergence Zone (ITCZ), along with large-scale seasonal
wind reversals (Gadgil 2003; Schneider et al. 2014).
The Himalayas and the Hindu Kush mountains protect the
Indian subcontinent from large-scale incursions of cold
extra-tropical winds during the winter season. Additionally, the
seasonal warming of the Himalayas and the Tibetan Plateau
during the boreal summer sets up a north–south thermal contrast
relative to the tropical Indian Ocean, which is important for
initiating the large-scale summer monsoon circulation. The
climatological seasons in India are broadly classified as the
winter (December–January–February), pre-monsoon (March–
April–May), summer monsoon (June–July–August–September) and the post-monsoon (October–November) seasons.
A distinction of India’s climate is the exceptionally strong
seasonal cycle of winds and precipitation (Turner and Annamalai 2012). The Indian summer monsoon, also known as the
South Asian monsoon, is a major component of the global
climate (see Box 1.1 for a summary of monsoon processes over
the Indian subcontinent). In addition to monsoonal rains, areas
in the western Himalayas (WH) also receive substantial precipitation during the winter and early spring months from
eastward propagating synoptic-scale weather systems known as
the Western Disturbances that originate from the Mediterranean
region (e.g. Dimri et al. 2015; Hunt et al. 2018; Krishnan et al.
2019a, b) (Chap. 11). The Indian region is also prone to a wide
range of severe weather events and climate extremes, including
tropical cyclones, thunderstorms, heat waves, floods, droughts,
among others.
Box 1.1: Monsoon Processes over the Indian
subcontinent
Large-scale orographic features such as the Himalayas
and the Tibetan Plateau (e.g. Boos and Kuang 2010;
Turner and Annamalai 2012 and references therein); as
well as narrow mountains such as the Western Ghats
along the Indian west coast and the Arakan Yoma
mountains along the Myanmar coast (e.g. Xie et al.
2006; Rajendran and Kitoh 2008; Krishnan et al.
2013; Sabin et al. 2013) exert control on the distribution of monsoon precipitation over the Indian subcontinent. With moisture-laden winds from the
Arabian Sea, the Bay of Bengal and the Indian Ocean
feeding bountiful rains over vast areas in central-north
and northeast India, Western Ghats and peninsular
India, central-eastern Himalayas; the summer monsoon activity is sustained through feedbacks between
the monsoon circulation and the release of latent heat
of condensation by moist convective processes (Rao
1976; Krishnamurti and Surgi 1987).
The ISM is home to a variety of precipitation producing
systems, which include—monsoon onset vortices,
meso-scale systems and orographic precipitation, west–
north-west moving synoptic systems (lows and depressions) from the Bay of Bengal and Southeast Asia, slow
northward and westward propagating large-scale organized rainbands and mid-tropospheric cyclones, to name a
few (Rao 1976). Interactions among multiple scales of
motion (i.e. planetary, regional, synoptic, meso and
cumulus scales) render significant spatio-temporal
heterogeneity in the monsoon rainfall distribution over
the region. Warm rain processes during the summer
monsoon region are recognized to be dominant over the
Western Ghats and other areas in India, as evidenced from
the Tropical Rainfall Measurement Mission (TRMM)
Precipitation Radar (PR) satellite (e.g. Shige et al. 2017)
and aircraft measurements (e.g. Konwar et al. 2014). There
has been improved understanding of the three-dimensional
structure of latent heating associated with convective and
stratiform clouds during the summer monsoon season
based on the TRMM satellite observations (e.g. Houze
1997; Houze et al. 2007; Stano et al. 2002; Romatschke
and Houze 2011); as well as the monsoonal circulation
response to latent heating based on numerical simulation
experiments (e.g. Choudhury and Krishnan 2011;
Choudhury et al. 2018) in the recent decades.
Several areas in south-eastern peninsular India,
including areas covering the states of Tamil Nadu and
Andhra Pradesh, receive considerable rainfall during
the northeast monsoon (October–December) (Rajeevan et al. 2012). The northeast monsoon develops
following the withdrawal of the summer monsoon
rainy season when the northern landmass of India and
the Asian continent begins to cool off rapidly so that
high-pressure builds over northern India. The northeasterly monsoon winds from the northern areas gather
moisture from the Bay of Bengal and contribute to
precipitation over peninsular India and parts of Sri
Lanka (Turner and Annamalai 2012).
1 Introduction to Climate Change Over the Indian Region
3
Indian subcontinent and sets the context for understanding
the key aspects of climate change in the region.
1.1.1 Setting the Regional Context
The distinct topographical and geographical features of the
Indian subcontinent endow the region with widely varying climatic zones ranging from the arid Thar desert in the north-west,
Himalayan tundra in the north, humid areas in the southwest,
central and northeastern parts, together with diverse microclimatic areas that spread across the vast subcontinent. A dominant
feature of the regional climate is the Indian Summer Monsoon
(ISM), which is characterized by pronounced seasonal migrations of the tropical rain belts associated with the Inter-tropical
Convergence Zone (ITCZ), along with large-scale seasonal
wind reversals (Gadgil 2003; Schneider et al. 2014).
The Himalayas and the Hindu Kush mountains protect the
Indian subcontinent from large-scale incursions of cold
extra-tropical winds during the winter season. Additionally, the
seasonal warming of the Himalayas and the Tibetan Plateau
during the boreal summer sets up a north–south thermal contrast
relative to the tropical Indian Ocean, which is important for
initiating the large-scale summer monsoon circulation. The
climatological seasons in India are broadly classified as the
winter (December–January–February), pre-monsoon (March–
April–May), summer monsoon (June–July–August–September) and the post-monsoon (October–November) seasons.
A distinction of India’s climate is the exceptionally strong
seasonal cycle of winds and precipitation (Turner and Annamalai 2012). The Indian summer monsoon, also known as the
South Asian monsoon, is a major component of the global
climate (see Box 1.1 for a summary of monsoon processes over
the Indian subcontinent). In addition to monsoonal rains, areas
in the western Himalayas (WH) also receive substantial precipitation during the winter and early spring months from
eastward propagating synoptic-scale weather systems known as
the Western Disturbances that originate from the Mediterranean
region (e.g. Dimri et al. 2015; Hunt et al. 2018; Krishnan et al.
2019a, b) (Chap. 11). The Indian region is also prone to a wide
range of severe weather events and climate extremes, including
tropical cyclones, thunderstorms, heat waves, floods, droughts,
among others.
Box 1.1: Monsoon Processes over the Indian
subcontinent
Large-scale orographic features such as the Himalayas
and the Tibetan Plateau (e.g. Boos and Kuang 2010;
Turner and Annamalai 2012 and references therein); as
well as narrow mountains such as the Western Ghats
along the Indian west coast and the Arakan Yoma
mountains along the Myanmar coast (e.g. Xie et al.
2006; Rajendran and Kitoh 2008; Krishnan et al.
2013; Sabin et al. 2013) exert control on the distribution of monsoon precipitation over the Indian subcontinent. With moisture-laden winds from the
Arabian Sea, the Bay of Bengal and the Indian Ocean
feeding bountiful rains over vast areas in central-north
and northeast India, Western Ghats and peninsular
India, central-eastern Himalayas; the summer monsoon activity is sustained through feedbacks between
the monsoon circulation and the release of latent heat
of condensation by moist convective processes (Rao
1976; Krishnamurti and Surgi 1987).
The ISM is home to a variety of precipitation producing
systems, which include—monsoon onset vortices,
meso-scale systems and orographic precipitation, west–
north-west moving synoptic systems (lows and depressions) from the Bay of Bengal and Southeast Asia, slow
northward and westward propagating large-scale organized rainbands and mid-tropospheric cyclones, to name a
few (Rao 1976). Interactions among multiple scales of
motion (i.e. planetary, regional, synoptic, meso and
cumulus scales) render significant spatio-temporal
heterogeneity in the monsoon rainfall distribution over
the region. Warm rain processes during the summer
monsoon region are recognized to be dominant over the
Western Ghats and other areas in India, as evidenced from
the Tropical Rainfall Measurement Mission (TRMM)
Precipitation Radar (PR) satellite (e.g. Shige et al. 2017)
and aircraft measurements (e.g. Konwar et al. 2014). There
has been improved understanding of the three-dimensional
structure of latent heating associated with convective and
stratiform clouds during the summer monsoon season
based on the TRMM satellite observations (e.g. Houze
1997; Houze et al. 2007; Stano et al. 2002; Romatschke
and Houze 2011); as well as the monsoonal circulation
response to latent heating based on numerical simulation
experiments (e.g. Choudhury and Krishnan 2011;
Choudhury et al. 2018) in the recent decades.
Several areas in south-eastern peninsular India,
including areas covering the states of Tamil Nadu and
Andhra Pradesh, receive considerable rainfall during
the northeast monsoon (October–December) (Rajeevan et al. 2012). The northeast monsoon develops
following the withdrawal of the summer monsoon
rainy season when the northern landmass of India and
the Asian continent begins to cool off rapidly so that
high-pressure builds over northern India. The northeasterly monsoon winds from the northern areas gather
moisture from the Bay of Bengal and contribute to
precipitation over peninsular India and parts of Sri
Lanka (Turner and Annamalai 2012).
1 Introduction to Climate Change Over the Indian Region
3