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Ungauged and data-scarce coastal river catchments, small and medium-sized ones in particular, are popular worldwide, especially in developing countries in Southeast Asia. In general, coastal river catchments are exposed to various coastal hazards such as fluvial floods, typhoons, and sea-level rise. In addition, climate change and socio-economic development will substantially change global flood risks. However, in scientific research, flood risk and future flood risk assessments in such coastal river catchments have not been significantly considered. Therefore, the overall objective of this thesis is to propose an innovative methodological framework for modeling and evaluating flood risk in such river catchments in the future under the impacts of climate change, sea-level rise, and land-use change based on using numerical models (hydrological models and land-use change models) and remote sensing data (satellite images and precipitation) in combination with other state-of-the-art methods, tools and models, and new approaches, such as flood risk assessment methods, regionalization methods, and statistical downscaling methods. The proposed framework was adopted, applied, and validated successfully for a case study - Tra Bong River Catchment - on the south-central coast of Vietnam as a test application. The main conclusion of this research is that the proposed framework can provide valuable information and projections of changing future flood risk associated with climatic and socio-economic changes in ungauged and data-scarce coastal river catchments. The proposed framework is designed with free model and method choices, meaning that it can apply different methods and tools for each step depending on the natural characteristics of river catchments, data collection, tools, and understanding of models, etc. Finally, this research can be used as a technical reference for designing and building national, regional, or local frameworks/guidelines for assessing future flood risk in ungauged and data-scarce coastal river catchments in Vietnam and other countries in Southeast Asia.
In most studies on flood risk in Nigeria, priority is given to urban flood risk than rural flood risk. Smallholder farmers who mostly inhabit rural areas and flood plains are known to be at great risk of flooding, but to date, there have been no studies on the impacts they experience and how they cope with these impacts.
To establish the existence of significant change in precipitation in the study area, statistical analysis of precipitation data was conducted using linear regression and non-parametric Mann Kendall test. Landsat satellite images for 1986, 2003 and 2016 were obtained from the United States Geological Survey’s (USGS) website and used to collect and analyze data related to land use.
To determine flood risk in the context of land use change, the HEC-HMS model version 3.5 was used. Land use maps corresponding to 1986, 2003, and 2016 LULC conditions were analysed and prepared for the calculation of CN values using Soil Conservation Service (SCS-CN) method. CN map was prepared by integrating the maps of hydrologic soil groups and land use in ArcGIS software.
Based on selected morphological parameters, a flood risk map was developed for the study area. The morphologic flood risk showed that most parts of the basin face moderate flood risk. Higher runoff values were observed under 2016 LULC conditions mainly due to intense deforestation relative to those of 1986 and 2003. The results indicated that runoff and peak discharge are significantly affected by deforestation instead of changes in the rainfall pattern. Flood inundation maps of the study area were prepared for the flood events of 2012 and 2015. Maximum depth for the 2012 and 2015 flood events was calculated as 10.58m and 7.39m, respectively.
The socioeconomic aspects of the research were conducted using household survey method. Using snowball sampling techniques, 400 flood-affected households were selected. The results show that the adaptive capacity of smallholder farmers in the study area remains very low and hampered by several factors such as poverty and weakened social networks. The synopsis of the examined variables leads to the following conclusion: Instead of climatic factors – as one indicator of vulnerability – it is social inequality and poverty in the region as well as the structural economic differences between various groups that mainly drives vulnerability in the study area.
Improvement of flood risk assessment under climate change in Ho Chi Minh City with GIS applications
(2014)
Ho Chi Minh City is the largest city in VN. The city is the most important center of economy, society and culture in the southern region of Vietnam. However, due to characteristics of natural conditions with low topography and borders touch the sea so that since the late 20th century with the rapid economic and urban development there are environmental problems have arisen. One of the problems is flooding issue caused by high tide. With these natural conditions and sea level rise of climate change in the future, Ho Chi Minh City is considered as one of the most affected and damaged cities in the world.
Therefore, many policies have been set out from the national to local levels in Vietnam to prepare for adaptability of impacts and risks of the sea level rise and the climate change. And this has also been considered in Ho Chi Minh City as the development policies of the city authorities have to consider in the context of the sea level rise and the climate change. A number of researches have been conducted to assess the impact of climate change to Ho Chi Minh City in the future. However, these researches are still need to be enhanced further.
The flooding problem is a major issue of the sea level rise in Ho Chi Minh City. And to make a good result, the flood model needs a lot of requirements that ensure fine quality of input data, suitable model and a relied procedure. In the available research, the input data is not really the highest quality in the available context in Ho Chi Minh City. As the flood model is implemented, one of the input data requirements of the model is information detail of elevation in the flooded area. And this is more necessary than in geophysical urban areas such as Ho Chi Minh City. And to assess fully flood risk issues for flooding caused by tidal phenomenon in Ho Chi Minh City, the determination of many characteristics of flood model is very useful for users who need to apply the results of the model for the planning development in Ho Chi Minh City in the future. Besides adopting a uniform environment as GIS for managing all the data of flooding problem and making conditions for the development of decision support systems is very necessary for flood management in the future.
The research has been carried out and its results have been generated on the flood risk assessment associated context of the sea level rise due to climate change with high emissions scenario A1FI in 2030 for the current houses, the population and the land use types. The results have shown a lot of the areas where are inundated in the future with the increasing flooding duration, depth and frequency even though they are not flooded at the current because there are some protective structures. This will be helpful for suggesting a forecast of the development direction to decision makers in Ho Chi Minh City for next time period.
And the last part is the proposal for decision and policy makers, authorities and planners as well. Moreover, the results of this research can be used as the references and the foundations for further researches and so that the problems that Ho Chi Minh City may be encountered due to flood risk caused by climate change to the economic and social aspects of the development in Ho Chi Minh City will encounter. And the problem of adaptation to climate change will be more completed and more thoroughly so that it is to minimize the damage of climate change for the city.