Precipitation changes in India) are suggested to be the possible reasons for the intensification of river floods during
post-1950 period, in addition to the anthropogenic induced
changes in the catchment and river hydrology (Kale 2012).
The increasing trend in floods is also possibly attributed to
long-term climate variability (Ward et al. 2016; Najibi and
Devineni 2018).
6.3.1 Urban/Coastal Floods
In general, urban areas are prone to river or flash flooding.
Additionally, the major factors for urban floods include the
effect of anthropogenic geographical alterations, inadequate
drainage and storm water management system as well as
high structural inhomogeneity due to intense land-use
changes in proportion to increased urban population, and
also the increasing population (Carvalho et al. 2002; Shepherd 2005; Goswami et al. 2010; Yang et al. 2015; Liu and
Niyogi 2019). Under global warming, the observed
increasing trend in heavy rainfall events has resulted in more
frequent and intense flash floods over urban areas (Kishtawal
et al. 2010; Guhathakurta et al. 2011; Mishra and Lilhare
2016). It is also reported that the regions which are not
traditionally prone to floods experience severe inundation
due to downpour and cloud burst during recent decades.
The major urban flood events of India have occurred in
Mumbai (2005, 2014, 2017), Bangalore (2005, 2007, 2015),
Chennai (2002, 2004, 2005, 2006, 2007, 2015), Ahmadabad
(2017) and Kolkata (2007, 2017). It is to be noticed that
three major metropolitan Indian cities experienced severe
flooding in the same year 2005, i.e. Mumbai in July 2005,
Bangalore and Chennai in October and December 2005,
respectively (Guhathakurta et al. 2011). In the case of
Mumbai flood of 2005, apart from about 944 mm rainfall
recorded in 24-h, the intrusion of sea water into the city
resulted in mass inundation due to the complex drainage
system (Gupta and Nikam 2013). Studies also suggest that
Mumbai region is highly vulnerable to climate change due to
sea-level rise, storm surge and extreme precipitation (Hallegatte et al. 2010). The coastal city of Kolkata is also prone
to flooding due to extreme rainfall activities associated with
tropical cyclones. The subsidence of land in this region
combined with high-tide results in heavy flooding and is a
major problem for the river-side dwellers of the city which
could be exacerbated in this era of climate change (Dasgupta
et al. 2013). The Chennai city is more prone to tropical
disturbances, and cyclones, which often leads to flooding of
major rivers and clogging of drainage systems (Boyaj et al.
2018). A major flood event occurred in December 2015 was
reported as one of the most disastrous floods in the history of
the region (Assessment AR 2016, vandenborgh et al. 2016).
In spite of numerous flood occurrences, there is a knowledge
gap in assessing the impact of climate change on flooding
over urban areas. However, floods in Mumbai and Kolkata
are attributed to the impact of climate shifts, urbanization,
sea-level rise and other regional factors.
6.3.2 River Floods
The major river basins of South Asia such as the Brahmaputra, Ganga, Meghna, Narmada, Godavari and Mahanadi are
mainly driven by the SW and NE monsoons apart from snow
and glacier melt for Himalayan rivers (Mirza 2011). River
basin scale flooding is generally due to the occurrence of
extreme rainfall as well as variations in the factors associated
with the basin catchment characteristics (e.g. Mishra and
Lilhare 2016). Several intense floods were recorded in all the
large river basins in South Asia during the second half of the
twentieth century, such as the 1968 flood in the Tapi river, the
1970 flooding of the Narmada, the 1978 and 1987 floods on
the Ganga, the 1956 and 1986 floods in the Indus river, the
1979 flood of the Luni river, the 1982 flooding of the
Mahanadi river, the 1986 flooding of the Godavari river, the
1988 and 1998 floods of the Brahmaputra and the catastrophic
flood of 2010 along the Indus basin (Kale 2012). River basins
located in Central India, i.e. Ganga, Narmada-Tapi and
Godavari, exhibit a significant increasing trend in the area
covered by heavy rainfall episodes, during the monsoon
season for the period 1951–2014 (Deshpande et al. 2016),
which has lead to increased flooding over these basins. The
increase in flood events over the Ganga-Brahmaputra basin is
compounded by subsidence of land (Higgins et al. 2014) as
well as glacier and water from snowmelt feeding into these
rivers (Lutz et al. 2014). Hence, in a global warming scenario,
melting of glaciers and snow could get accelerated and could
lead to larger flood risks in the Himalayan rivers.
River floods are found to have a close association with
ENSO events. A strong connection between rainfall over the
Ganga-Brahmaputra-Meghna basin and the Southern Oscillation Index (SOI) was identified (Chowdhury 2003), with
less than normal rainfall during the negative phase of the
SOI (El Niño) whereas severe flooding due to significant
increase in rainfall during positive SOI (La Niña). Moreover,
major floods over the basin have occurred during La Niña
years and also La Niña years co-occurring with negative
IOD events (Pervez and Henebry 2015). The extreme floods
across the Brahmaputra river in 1988 (Bhattacharyya and
Bora 1997), 1998 (Dhar and Nandargi 2000), 2012, 2016,
2017; over the Narmada river in 1970, 2012, 2016 and over
the Indus river in 1956, 1973, 1976, 2010 (Houze et al. 2011;
6 Droughts and Floods
129
post-1950 period, in addition to the anthropogenic induced
changes in the catchment and river hydrology (Kale 2012).
The increasing trend in floods is also possibly attributed to
long-term climate variability (Ward et al. 2016; Najibi and
Devineni 2018).
6.3.1 Urban/Coastal Floods
In general, urban areas are prone to river or flash flooding.
Additionally, the major factors for urban floods include the
effect of anthropogenic geographical alterations, inadequate
drainage and storm water management system as well as
high structural inhomogeneity due to intense land-use
changes in proportion to increased urban population, and
also the increasing population (Carvalho et al. 2002; Shepherd 2005; Goswami et al. 2010; Yang et al. 2015; Liu and
Niyogi 2019). Under global warming, the observed
increasing trend in heavy rainfall events has resulted in more
frequent and intense flash floods over urban areas (Kishtawal
et al. 2010; Guhathakurta et al. 2011; Mishra and Lilhare
2016). It is also reported that the regions which are not
traditionally prone to floods experience severe inundation
due to downpour and cloud burst during recent decades.
The major urban flood events of India have occurred in
Mumbai (2005, 2014, 2017), Bangalore (2005, 2007, 2015),
Chennai (2002, 2004, 2005, 2006, 2007, 2015), Ahmadabad
(2017) and Kolkata (2007, 2017). It is to be noticed that
three major metropolitan Indian cities experienced severe
flooding in the same year 2005, i.e. Mumbai in July 2005,
Bangalore and Chennai in October and December 2005,
respectively (Guhathakurta et al. 2011). In the case of
Mumbai flood of 2005, apart from about 944 mm rainfall
recorded in 24-h, the intrusion of sea water into the city
resulted in mass inundation due to the complex drainage
system (Gupta and Nikam 2013). Studies also suggest that
Mumbai region is highly vulnerable to climate change due to
sea-level rise, storm surge and extreme precipitation (Hallegatte et al. 2010). The coastal city of Kolkata is also prone
to flooding due to extreme rainfall activities associated with
tropical cyclones. The subsidence of land in this region
combined with high-tide results in heavy flooding and is a
major problem for the river-side dwellers of the city which
could be exacerbated in this era of climate change (Dasgupta
et al. 2013). The Chennai city is more prone to tropical
disturbances, and cyclones, which often leads to flooding of
major rivers and clogging of drainage systems (Boyaj et al.
2018). A major flood event occurred in December 2015 was
reported as one of the most disastrous floods in the history of
the region (Assessment AR 2016, vandenborgh et al. 2016).
In spite of numerous flood occurrences, there is a knowledge
gap in assessing the impact of climate change on flooding
over urban areas. However, floods in Mumbai and Kolkata
are attributed to the impact of climate shifts, urbanization,
sea-level rise and other regional factors.
6.3.2 River Floods
The major river basins of South Asia such as the Brahmaputra, Ganga, Meghna, Narmada, Godavari and Mahanadi are
mainly driven by the SW and NE monsoons apart from snow
and glacier melt for Himalayan rivers (Mirza 2011). River
basin scale flooding is generally due to the occurrence of
extreme rainfall as well as variations in the factors associated
with the basin catchment characteristics (e.g. Mishra and
Lilhare 2016). Several intense floods were recorded in all the
large river basins in South Asia during the second half of the
twentieth century, such as the 1968 flood in the Tapi river, the
1970 flooding of the Narmada, the 1978 and 1987 floods on
the Ganga, the 1956 and 1986 floods in the Indus river, the
1979 flood of the Luni river, the 1982 flooding of the
Mahanadi river, the 1986 flooding of the Godavari river, the
1988 and 1998 floods of the Brahmaputra and the catastrophic
flood of 2010 along the Indus basin (Kale 2012). River basins
located in Central India, i.e. Ganga, Narmada-Tapi and
Godavari, exhibit a significant increasing trend in the area
covered by heavy rainfall episodes, during the monsoon
season for the period 1951–2014 (Deshpande et al. 2016),
which has lead to increased flooding over these basins. The
increase in flood events over the Ganga-Brahmaputra basin is
compounded by subsidence of land (Higgins et al. 2014) as
well as glacier and water from snowmelt feeding into these
rivers (Lutz et al. 2014). Hence, in a global warming scenario,
melting of glaciers and snow could get accelerated and could
lead to larger flood risks in the Himalayan rivers.
River floods are found to have a close association with
ENSO events. A strong connection between rainfall over the
Ganga-Brahmaputra-Meghna basin and the Southern Oscillation Index (SOI) was identified (Chowdhury 2003), with
less than normal rainfall during the negative phase of the
SOI (El Niño) whereas severe flooding due to significant
increase in rainfall during positive SOI (La Niña). Moreover,
major floods over the basin have occurred during La Niña
years and also La Niña years co-occurring with negative
IOD events (Pervez and Henebry 2015). The extreme floods
across the Brahmaputra river in 1988 (Bhattacharyya and
Bora 1997), 1998 (Dhar and Nandargi 2000), 2012, 2016,
2017; over the Narmada river in 1970, 2012, 2016 and over
the Indus river in 1956, 1973, 1976, 2010 (Houze et al. 2011;
6 Droughts and Floods
129