rainfall events nor the extraordinary floods occur
every year in the same basin. In order to determine whether the frequency of large floods has
increased in the last few decades of the twentieth
century, the largest floods were considered and
the decadal frequency was calculated. Hence, all
the floods on the rivers of BHB during the
twentieth century are not adequately represented
in Fig. 13.5.
Notwithstanding these limitations, it is quite
clear that the frequency of large and extreme
floods was higher during the five discrete decades in general (1900s, 1940s, 1950s, 1970s and
1990s). A significant link between the Indian
monsoon rainfall and 1970s and 1990s decade
floods is observed. But on the other hand, there is
no relation between excess flood occurrences and
rainfall events in the 1900s, 1940s and 1950s
Fig. 13.4 Multiple time
series plots of Cramer’s t
statistic for the 10-year
running means, depicting
decadal fluctuations in the
basin’s monthly rainfall for
eight major districts of West
Bengal
178
N. C. Jana et al.
every year in the same basin. In order to determine whether the frequency of large floods has
increased in the last few decades of the twentieth
century, the largest floods were considered and
the decadal frequency was calculated. Hence, all
the floods on the rivers of BHB during the
twentieth century are not adequately represented
in Fig. 13.5.
Notwithstanding these limitations, it is quite
clear that the frequency of large and extreme
floods was higher during the five discrete decades in general (1900s, 1940s, 1950s, 1970s and
1990s). A significant link between the Indian
monsoon rainfall and 1970s and 1990s decade
floods is observed. But on the other hand, there is
no relation between excess flood occurrences and
rainfall events in the 1900s, 1940s and 1950s
Fig. 13.4 Multiple time
series plots of Cramer’s t
statistic for the 10-year
running means, depicting
decadal fluctuations in the
basin’s monthly rainfall for
eight major districts of West
Bengal
178
N. C. Jana et al.