Impact Assessment of Climate Change and Sea Level Rise on ...

2. DATA <strong>and</strong> MODEL
2.1 Data Collection <strong>and</strong> Compilation
Reliable data are prerequisite to carry out flood frequency analysis, establish base conditions
on floods <strong>and</strong> l<strong>and</strong> type. Available water level <strong>and</strong> water flow time series, river bathymetry
<strong>and</strong> rainfall data were collected from secondary sources such as BWDB <strong>and</strong> BIWTA.
Bathymetry data were collected to develop <strong>and</strong> update the model bathymetry <strong>of</strong> Bay <strong>of</strong>
Bengal <strong>and</strong> other regional models Water level data <strong>and</strong> discharge data were collected to
generate boundaries <strong>and</strong> to re-calibrate the existing models. Rainfall data were collected for
development <strong>of</strong> rainfall-run<strong>of</strong>f model (NAM model). Coverage area <strong>of</strong> T-Aman in three
selected upazilas Bakerganj <strong>of</strong> Barisal district, Raiganj <strong>of</strong> Sirajganj district <strong>and</strong> Gobindaganj
<strong>of</strong> Gaib<strong>and</strong>ha district has been collected in consultation with each block supervisor <strong>of</strong>
corresponding upazila.
2.2 Available Models
2.2.1 GBM Basin Model
Background
The country’s unique geographical location with the Indian Ocean to the South, the
Himalayas to the north <strong>and</strong> the prevailing monsoons has made it one <strong>of</strong> the wettest countries
<strong>of</strong> the world. Bangladesh is probably the worst victim <strong>of</strong> excessive rainfall in the upper
catchment outside its territory. This external rainfall generates massive run<strong>of</strong>f <strong>of</strong> water that
reaches the Bay <strong>of</strong> Bengal through country’s territory. Almost all the major rivers have their
origins beyond the political border <strong>of</strong> the country, <strong>and</strong> thereby placing it in a disadvantageous
position to manage its own river systems.
There are 57 border rivers bringing inflows from India. About one-fourth to one-third <strong>of</strong> the
country is normally flooded to varying degrees each year during the period from May through
September. The major flood <strong>of</strong> 1998 caused inundation <strong>of</strong> about 70 % <strong>of</strong> the country. This
figure <strong>of</strong> flooding is expected to be more severe in future due to climate change <strong>and</strong> sea level
rise.
The GBM basin model was applied to reproduce the possible changes <strong>of</strong> monsoon flood in
the basin resulting from predicted hydro meteorological changes in the area. IWM carried out
this study through updating a previously developed simplified GBM basin model
incorporating up to date information. The model was used to compute run<strong>of</strong>fs generated from
basins <strong>of</strong> three major rivers, <strong>and</strong> thereby simulate the scenarios regarding monsoon flood in
the country introducing subsequent effect <strong>of</strong> climate change.
The prime objective <strong>of</strong> this study component “Updating <strong>of</strong> the GBM basin model” is
quantification <strong>of</strong> inflows generated from three major river basins under recent & changed
climate condition so that impact on monsoon flooding in Bangladesh resulting from climate
change <strong>and</strong> sea level rise as predicted in 4th assessment report <strong>of</strong> IPCC can be studied.
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