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Urban morphology is used in many developed countries to classify and manage the dis-tribution of urban functions. In urban planning, it helps to identify the emerging prob-lems and solve the disorder of urban functions. The megacity Ho Chi Minh City has faced many problems with uncontrollable urbanization, urban management and plan-ning. It has received increasing tropical storms and cyclones which caused more heavy rains in recent decades. Rapid urbanization has caused the increase of built-up coverage with disordered typologies, incomplete infrastructure and urban-peripheral instability. In the flooding context, these problems have increased more seriously with flooding impacts and caused uncontrollable planning and management in the city. This study applies the urban morphology method to measure flood impacts on urban functions and develop the adaptive solutions for flooding adaptation for Ho Chi Minh City. The methods in this study are based on applying fractal geometry, GIS and Remote Sensing on large-scale maps for measuring the urban morphology. The land-use map and the building footprints map of 2010 were founded to analyze the distribution of urban areas by high resolution of satellite images and large scale GIS data. The fractal geometry was a setting based on Avenue program of Arcview GIS to measure the urban morphology. This formed a key input for the multi-criteria analysis (MCA) method that investigated the cause of flood impacts and suggested the solution for flooding adapta-tion. In addition, alterations of lakes, ponds and watercourse from 1995 to 2009 were explored. The study showed HCMC had problems on irrational development in residential densi-ties areas and urban functions, and the uneven development of population and residen-tial density between the urban areas: too much in the urban districts (about 300 to 500 persons per hectare per block and coverage ratio 0.7 - 0.9). This pushed the increasing demand on built-up area and filled-up rivers and canals (About 80 percent of original ponds and lakes in inner-center were filled-up in the past; and 63 percent of ponds and lakes have been filled-up in Sub-Districts and new-urban-development areas). It made the imbalance between the permeability of land surface and the run-off water flows; then leads the inundation to increase. This is the main reason for reducing the water-storage capacity in rainy season. Flooding in urban residential area was more im-pacted than in rural residential area, higher level and longer flood time; while flooding in the rainy season due to high tides, heavy rains or both was the emerging and uncon-trollable problems. For flooding adaptation, urban morphology analysis helped to figure out the potential areas in the city could be used for reducing flooding impacts in urban areas. There are many low-density residential areas in above 1.5 meter AMSL areas in the North, Northwest and Northeast areas of the city which could be developed with complete infrastructure and urban services to attract people from high-density residential areas impacted deeply by floods in the center. These potential areas could be the long-term strategic solution to flooding adaptation for HCMC. The results also suggested that some current flooded areas would be re-planned or returned to be the water-storage and permeable areas (such as green parks, ponds and lakes). This re-planning would improve the city landscape and increase the permeable surface, green spaces and open spaces to HCMC. More green spaces, lakes and ponds will also help to reduce the temperature of urban center in the dry season. This adaptation solution would reduce at least 25 percent of current flooded areas in urban center. The protection and constructed restriction of current agricultural areas in peri-urban Districts would maintain the infil-tration and green-tree areas. Furthermore, the complete drainage system would help to reduce better flood for these areas. Finally, fully dredging river and canal system of the city would reduce about 25 to 30 percent of current flooded areas.
Historically as a city situated in a low-lying area a Ho Chi Minh City has been exposed to floods. Ho Chi Minh City is a megacity with uncontrollable urbanization and dynam-ic economies. In recent years, flood has become a serious problem with a multitude of follow-on impacts. It received more heavy rains affected by tropical storms and cy-clones. Further urbanization and future changes in climate are likely to increase flood risks. People have faced the flood impacts on the socioeconomic aspects in recent dec-ades. This study researched on 450 households in different spaces of the inner center (old districts), developed center (urban districts) and new-developing areas (peri-districts) and in different geographical elevations to identify the impacts of flooding in various space and time; and various problems on households’ socioeconomic aspects in flood residential areas. The multi-criteria analyses in GIS and with of the combination SPSS analysis, the sur-veyed households were identified by their location on the topographic map to clarify the flooding reasons and the types of flood in the areas. The 450 households were chosen in flood residential areas and selected in three categories of characteristics: (1) 150 poor households in flood housing areas; (2) 150 poor households in non-flood housing areas; and (3) 150 higher-income households in non-flood housing areas. This disparity was to analyze the different flood impacts on socioeconomic aspects and on household capitals amongst them. The linear regression in SPSS analysis was used to clarify the relation-ships between flood types with space factor (geographical elevation) and time factors (flood months in year, and flood years in residential areas). This test gave the supports to the reliability of the study results. By geographical elevation analysis, flood impacted on the areas in three main types: (1) flood by rain; (2) flood by tide; and (3) flood by both rain and tide. The tidal flood oc-cupied the low-elevation areas; flood by rain invaded the widespread higher-elevation areas; and the mix type of flood occupied the transition areas between flood areas by rain and by tide. Lower land had the deeper flood level, however; many of high-land areas were flooded in this city. Flood in residential areas had caused flood problems on streets, sidewalks (housing pavements), residential drainage system, water supply and electric power. In the poor households of Group One, flood in residential areas impacted their housing areas. To protect housing from flooding, many households had to invest their income for house rising or rebuilding or pavement rising, etc. They also privately invested for repairing or new buying their housing facilities, furniture and other appli-ances. Their income was lost and deficit. To the household capitals analysis, households were impacted more on physical, financial, natural and human capitals. The poor households in Group One had the most vulnerabilities amongst three groups, whilst there was no support from social organizations and government at levels. The household strategies developed in this study are to support people in flood and flood-prone areas conserving their capabilities to achieve the strategic outcome for sustainable develop-ment.
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.