Cyclone and Storm Surge - Iczmpwb.org

4.11
4.5. Assessment of Storm surge
Storm surge is a phenomenon where the tide level rises mainly due to drifted seawater and a drop in
atmospheric pressure when a low pressure system approaches. The hazard level of storm surge
inundation is assessed by estimating the seawater inflow due to storm surges in the assessment
area and the depth of inundation and other factors which are used as indices of damage.
The east coast of India is frequently affected by storm surges. Most vulnerable portions of the east coast
are Orissa, West Bengal and south Andhra coasts. To cite some of the destructive cyclones over the
Bay of Bengal are 1977 Andhra Cyclone, 1999 Orissa Super cyclone, 1970 Bhola cyclone etc., where
reported loss of lives are enormous. In recent past, the loss of life is considerably reduced compared to
the earlier extreme events. The reason is improvement in the forecasting methods and timely evacuation
of people from the vulnerable areas. There can be little doubt that the number of causalities would have
been considerably lower if the surge could have been predicted, say, 24 hours in advance allowing
effective warnings in the vulnerable areas. The prediction, must, of course, be accurate enough so that
one can distinguish between the dangerous surges and the surges that cause little harm, as people
can not be evacuated from the exposed areas for every approaching storm. To note, success have
been achieved in predicting storm surges through operational numerical models.
Operational numerical storm surge prediction models have been developed and are being routinely used
for several coastal regions of the world such as: Storm Tide Warning Service (STWS) in the UK;
operational systems in the Netherlands and National Marine Environmental Forecasting centre in China.
A review of these operational forecasting system models is given in Jiping et al.(1990), Jelesnianski
(1989), Murty (1984) and Sundermann and Lenz (1983). The development of operational numerical
storm surge prediction system in India is an active thrust area which needs immediate attention, where
most of these models require large computational resources. Hence, for routine forecasting of storm
surges providing multiple forecast scenarios, the models cannot be used in the absence of adequate
computing facility. To overcome this difficulty, most of the forecasting offices including India
Meteorological Department (IMD) use the nomogram method for prediction of storm surges
associated with tropical cyclones. These nomograms are produced based on sensitivity analysis of
modeling studies conducted for varied bathymetries and approach angles.
The second WMO International workshop on tropical cyclones recommended the use of personal
computers (PCs) by the developing countries in order to adopt the stand-alone storm-surge forecasting
system. Recent advent of powerful personal computers has opened up the possibility of running
dynamical models in real time on PC-based work stations in an operational office. In fact, a PC-based