46
Md. A. Sattar and K. K. W. Cheung
and 6 m for the AS. When all cases are considered, the mean value of the maximum
surge (middle line in Fig. 3.4a) for the BoB was estimated to be almost double of
that for the AS.
For the future TC scenario, there is a significant increase in estimated surge height
especially for the AS basin (Fig. 3.4b). Mean surge level is about 2.5 m for both basins,
while the two extreme cases are both about 8 m in surge height. There is consequently
a clear increase in future surge level for AS compared to the climatology period. For
the BoB, the mean surge height only increases slightly, however, the spread towards
the high extreme surge levels has also been increased.
3.7 Past and Future Spatial Variations in Surge Height
It is also important to note that the surge level varies spatially over the NIO because
of its topography and tidal effects (the latter not simulated in this study). TCs with
similar intensities will result in different surge levels due to their formation and landfall locations. To demonstrate the impact of landfall location to surge level both for
the AS and BoB basins, we compare surge levels for landfalls with similar TC intensity. For instance, two TCs with similar intensity are compared: one made landfall to
the western part and another made landfall close to Bangladesh (Fig. 3.5a, b). These
two cases resulted in very differrent surge levels (with maximum surge of about 2.1 m
versus 7 m, respectively). Such contrasting surge levels are also found in other TCs
cases (not shown). As discussed in the model validation section, this large diffrence
in surge level may be due to differences in terms of coastal elevation, landfall location, wind speed, radius of mamimum sustanined wind, strength of storm winds and
storm’s forward speed, etc.
Similar cases can be identified for the AS basin as well. TC 3A (Gonu) had
intensity 127 kt during 2007 before making landfall over western part of AS, and the
TC caused only 0.8 m surge height (Fig. 3.5c). In contrast, TC 2A during 1999 had
lower intensity of 105 kt while making landfall over the eastern part of the AS coast,
and it generated a maximum surge height of about 6 m (Fig. 3.5d). It can be seen
that similar track types like these two cases over the AS can be identified in future
climate scenarios.
In the future scenario it is expected that surge height increases in the eastern part
of AS and BoB (including the Bangladesh coast of BoB) according to the simulated
tracks. This study simulated higher surge levels for the TCs that will make landfall
over eastern part than the western part of both the basins. Despite of similar wind
intensities, almost for all the cases lower surge levels have been estimated for TC
landfalls over western part of the basins. Example results are shown in Fig. 3.6 and
their tracks are presented in Fig. 3.7. We estimated maximum surge level 2.2 m for
the simulated TC B1930 whose wind intensity may reach up to 78.73 kt and it may
hit the western part of BoB in 2081 (Fig. 3.7a). On the other hand, we estimated
surge level 5.5 m for another less intense TC B4631that is expected to make landfall
over the eastern part of BoB (Fig. 3.7b). Similar patterns can be found over the AS
Md. A. Sattar and K. K. W. Cheung
and 6 m for the AS. When all cases are considered, the mean value of the maximum
surge (middle line in Fig. 3.4a) for the BoB was estimated to be almost double of
that for the AS.
For the future TC scenario, there is a significant increase in estimated surge height
especially for the AS basin (Fig. 3.4b). Mean surge level is about 2.5 m for both basins,
while the two extreme cases are both about 8 m in surge height. There is consequently
a clear increase in future surge level for AS compared to the climatology period. For
the BoB, the mean surge height only increases slightly, however, the spread towards
the high extreme surge levels has also been increased.
3.7 Past and Future Spatial Variations in Surge Height
It is also important to note that the surge level varies spatially over the NIO because
of its topography and tidal effects (the latter not simulated in this study). TCs with
similar intensities will result in different surge levels due to their formation and landfall locations. To demonstrate the impact of landfall location to surge level both for
the AS and BoB basins, we compare surge levels for landfalls with similar TC intensity. For instance, two TCs with similar intensity are compared: one made landfall to
the western part and another made landfall close to Bangladesh (Fig. 3.5a, b). These
two cases resulted in very differrent surge levels (with maximum surge of about 2.1 m
versus 7 m, respectively). Such contrasting surge levels are also found in other TCs
cases (not shown). As discussed in the model validation section, this large diffrence
in surge level may be due to differences in terms of coastal elevation, landfall location, wind speed, radius of mamimum sustanined wind, strength of storm winds and
storm’s forward speed, etc.
Similar cases can be identified for the AS basin as well. TC 3A (Gonu) had
intensity 127 kt during 2007 before making landfall over western part of AS, and the
TC caused only 0.8 m surge height (Fig. 3.5c). In contrast, TC 2A during 1999 had
lower intensity of 105 kt while making landfall over the eastern part of the AS coast,
and it generated a maximum surge height of about 6 m (Fig. 3.5d). It can be seen
that similar track types like these two cases over the AS can be identified in future
climate scenarios.
In the future scenario it is expected that surge height increases in the eastern part
of AS and BoB (including the Bangladesh coast of BoB) according to the simulated
tracks. This study simulated higher surge levels for the TCs that will make landfall
over eastern part than the western part of both the basins. Despite of similar wind
intensities, almost for all the cases lower surge levels have been estimated for TC
landfalls over western part of the basins. Example results are shown in Fig. 3.6 and
their tracks are presented in Fig. 3.7. We estimated maximum surge level 2.2 m for
the simulated TC B1930 whose wind intensity may reach up to 78.73 kt and it may
hit the western part of BoB in 2081 (Fig. 3.7a). On the other hand, we estimated
surge level 5.5 m for another less intense TC B4631that is expected to make landfall
over the eastern part of BoB (Fig. 3.7b). Similar patterns can be found over the AS