over most of western India including Deccan
Plateau and a decreasing to a neutral trend over
the eastern half of the country except the northeastern corner. Singh et al. (2008) indicated the
increasing trends in annual rainfall and relative
humidity during the period of 1901–2000 in
North Indian river basins. The temporal variation
in monthly, seasonal and annual rainfall during
the period of 1871–2005 was examined by
Krishnakumar et al. (2009) in Kerala. They
found the decreasing trend in southwest monsoon
while increasing trend in post-monsoon season.
The study conducted by Kumar and Jain (2010)
indicated the decrease in rainfall at four stations
and increase at one station in the Kashmir Valley.
Recently, Patra et al. (2012) have also detected
rainfall trends in twentieth century over Orissa
state. They found no trend in annual series as
well as monsoon rainfall for the period of 1871–
2006, whereas increasing trend in post-monsoon
season of Orissa.
However, so far there is no comprehensive
study on long-term and short-term behavior of
rainfall
in
Bhagirathi-Hooghly
Basin
(BHB) which falls in the direct path of monsoon
disturbances originating from the Bay of Bengal.
Actually, the monsoon disturbances are known to
be one of the major synoptic weather systems
that are responsible for heavy rainfall and large
floods on the rivers of BHB. So, rainfall trend
analysis within the basin is important and the
outcomes of this study will be highly useful for
the planning and management of water resources
in the basin. Keeping the above in background,
the present research is aimed at analyzing trends
in rainfall data series (1901–2000) of BHB and to
probe into the linkage between flood-rich periods
and excess monsoon rainfall. The BHB was
selected for this study as it is one of the important
river basins in West Bengal, India where agriculture plays a vital role in the economy. It is a
part of western Ganga–Brahmaputra deltaic plain
and one of the recognized climatically vulnerable
regions of India. Recent occurrences of the
extreme floods in this basin underscore the
importance of evaluating the trend and variability
of rainfall in order to understand the potential
impact of future change. In this context, this
study will not only improve our understanding of
the large-scale global atmospheric dynamics
(monsoons), but will also provide insight for
understanding future changes in large floods visà-vis monsoon intensity.
13.2 Study Area
This portion of West Bengal, south of the
Padma, together with a good chunk of the
Chotanagpur plateau, over which extends the
catchments of the western tributaries, comprise
the hydrological basin of the BhagirathiHooghly (Bagchi 1972b). It is one of the most
important feeder rivers of the Ganges Delta
which takes off on the right bank of the River
Ganga at Mithipur in the district of Murshidabad
and after traversing a distance of 570 km falls
into the Bay of Bengal (Fig. 13.1). It drains an
area of *17,350 km
2 between 85°45′ E and 89°
E longitude and 21°33′ N to 24°51′30” N latitude (Basu 1967, 2005; Mukhopadhyay and
Dasgupta 2010). The non-tidal part of the river
extending from the off-take to Nabadwip, a
distance of about 248 km, is known as the
Bhagirathi while the tidal reach from Nabadwip
to the Bay, a length of about 322 km, is known
as the Hooghly. It is distinct from the others in
that it is not merely a spill channel but carries an
independent supply of water from its western
tributaries such as the Bansloi, the Pagla, the
Mayurakshi-Babla, the Ajay and the Khari join
the upstream of Bhagirathi-Hooghly while the
Damodar, the Silabati-Rupanarayan, the
Kangsabati-Haldi and Rasulpur join the downstream of it (Rudra 2010). The western tributaries bring in a considerable amount of
sediment load along with their freshets from the
upper catchments and this huge detritus load
plays a significant role on the regime of basin
(Bagchi 1972a). The hydrological basin of this
river including the old alluvial flood plains of its
tributaries is recognized as climatic vulnerable
13 Changing Rainfall Patterns and Their Linkage to Floods …
171
Plateau and a decreasing to a neutral trend over
the eastern half of the country except the northeastern corner. Singh et al. (2008) indicated the
increasing trends in annual rainfall and relative
humidity during the period of 1901–2000 in
North Indian river basins. The temporal variation
in monthly, seasonal and annual rainfall during
the period of 1871–2005 was examined by
Krishnakumar et al. (2009) in Kerala. They
found the decreasing trend in southwest monsoon
while increasing trend in post-monsoon season.
The study conducted by Kumar and Jain (2010)
indicated the decrease in rainfall at four stations
and increase at one station in the Kashmir Valley.
Recently, Patra et al. (2012) have also detected
rainfall trends in twentieth century over Orissa
state. They found no trend in annual series as
well as monsoon rainfall for the period of 1871–
2006, whereas increasing trend in post-monsoon
season of Orissa.
However, so far there is no comprehensive
study on long-term and short-term behavior of
rainfall
in
Bhagirathi-Hooghly
Basin
(BHB) which falls in the direct path of monsoon
disturbances originating from the Bay of Bengal.
Actually, the monsoon disturbances are known to
be one of the major synoptic weather systems
that are responsible for heavy rainfall and large
floods on the rivers of BHB. So, rainfall trend
analysis within the basin is important and the
outcomes of this study will be highly useful for
the planning and management of water resources
in the basin. Keeping the above in background,
the present research is aimed at analyzing trends
in rainfall data series (1901–2000) of BHB and to
probe into the linkage between flood-rich periods
and excess monsoon rainfall. The BHB was
selected for this study as it is one of the important
river basins in West Bengal, India where agriculture plays a vital role in the economy. It is a
part of western Ganga–Brahmaputra deltaic plain
and one of the recognized climatically vulnerable
regions of India. Recent occurrences of the
extreme floods in this basin underscore the
importance of evaluating the trend and variability
of rainfall in order to understand the potential
impact of future change. In this context, this
study will not only improve our understanding of
the large-scale global atmospheric dynamics
(monsoons), but will also provide insight for
understanding future changes in large floods visà-vis monsoon intensity.
13.2 Study Area
This portion of West Bengal, south of the
Padma, together with a good chunk of the
Chotanagpur plateau, over which extends the
catchments of the western tributaries, comprise
the hydrological basin of the BhagirathiHooghly (Bagchi 1972b). It is one of the most
important feeder rivers of the Ganges Delta
which takes off on the right bank of the River
Ganga at Mithipur in the district of Murshidabad
and after traversing a distance of 570 km falls
into the Bay of Bengal (Fig. 13.1). It drains an
area of *17,350 km
2 between 85°45′ E and 89°
E longitude and 21°33′ N to 24°51′30” N latitude (Basu 1967, 2005; Mukhopadhyay and
Dasgupta 2010). The non-tidal part of the river
extending from the off-take to Nabadwip, a
distance of about 248 km, is known as the
Bhagirathi while the tidal reach from Nabadwip
to the Bay, a length of about 322 km, is known
as the Hooghly. It is distinct from the others in
that it is not merely a spill channel but carries an
independent supply of water from its western
tributaries such as the Bansloi, the Pagla, the
Mayurakshi-Babla, the Ajay and the Khari join
the upstream of Bhagirathi-Hooghly while the
Damodar, the Silabati-Rupanarayan, the
Kangsabati-Haldi and Rasulpur join the downstream of it (Rudra 2010). The western tributaries bring in a considerable amount of
sediment load along with their freshets from the
upper catchments and this huge detritus load
plays a significant role on the regime of basin
(Bagchi 1972a). The hydrological basin of this
river including the old alluvial flood plains of its
tributaries is recognized as climatic vulnerable
13 Changing Rainfall Patterns and Their Linkage to Floods …
171