Résumé
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Climate change
due to the increase
of greenhouse gas emissions is considered to be one of the major
challenges to
mankind in the 21st
century. It will lead to changes in precipitation, atmospheric
moisture,
increase in evaporation and probably a higher frequency of extreme
events. The
consequences of these phenomena will have an influence on many aspects
of human
society. Particularly at river deltas, coastal regions and developing
countries, the impacts of climate change to socio-economic development
become
more serious. So there is a need for a robust and accurate estimation
of the
variation of natural factors due to climate change, at least in the
hydrological cycle and flooding events to provide a strong basis for
mitigating
the impacts of climate change and to adapt to
these challenges.
Vietnam is located in
the region of
the south East Asia monsoon. As most
of the
population works in agriculture and inhabitants essentially concentrate
at the
coastal plain, Vietnam is expected to be one of the most heavily
countries affected
by the consequences of climate change in the end of 21st century. These
challenges urge Vietnam
to have suitable policies which help to improve public awareness, as
well as
capacity to respond to climate change. In order to provide complete
insights
for local authority to establish better adaptation strategies against
the
climate change, the PhD thesis focuses on simulating the long term
variation of
runoff factors for a river system in central Vietnam, the Vu Gia Thu
Bon River.
The first part of
this study
concentrates on constructing a hydrological model which becomes an
efficient
tool for assessing the variation of stream flow in the future. Due to
its
advantages, the fully deterministic distributed hydrological model,
which is
expected to overcome the difficulties in hydrological modelling at
large
catchment and the lack of data, is chosen for applying in Vu Gia Thu
Bon
catchment. The model is set up over Vu Gia Thu Bon catchment,
approximately
10,350 km2. This model considers mostly the runoff factors, from
surface flow
to groundwater flow, from infiltration to evapo-transpiration. This
model is
calibrated and validated against daily data and monthly data in the
period of
1991-2000 and 2001-2010, respectively. The second part is to evaluate
the impact
of climate factor changes on runoff at the end of he 21st century. For
this
purpose, 3 climate scenarios (CCSM3.0,MIROC-3.2,ECHAM5) for the period
2091-2100 were estimated from the present observations of the period
1991-2000
by using delta change factors obtained from downscaling process. These
scenarios were input to the validated hydrological model for
determining the
runoff in the future. The change tendency is shown by the difference in
the
present and future peak flow, base flow and return period. In the third
part, a
hydraulic model has been developed for the flood prone area (1,780 km2)
to map
the inundation area corresponding with the previously described
streamflow
variations. Scale variability of inundation area under the impact of
climate
change was evaluated to demonstrate the severe consequences of global
warming
at Vu Gia Thu Bon catchment. Finally, flood and land use maps are
analyzed to
estimate damages caused by the streamflow increase.) To map the
inundation area
corresponding with the previously described streamflow variations,
scale
variability of inundation area under the impact of climate change was
evaluated
to demonstrate the severe consequences of global warming at Vu Gia Thu
Bon
catchment. Finally, flood and land use maps are analyzed to estimate
damages
caused by the streamflow increase.
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