In recent years, flooding in Ho Chi Minh city has become more and more serious, it affects the lives of the citizens very much. There are some reasons which cause this situation, among them the rapid urbanization is the main one. In two last decades, Ho Chi Minh city became the biggest industrial, commercial, scientific, technological and tourist center of Vietnam, with numerous buildings mushrooming and a fast population increase, creating many residential areas. Many areas, that were water storages before, now are filled up with building constructions, some canals are blocked by houses or rubbish from the inhabitants, the drainage is too old and therefore always overloaded when the rain comes, the water cannot withdraw, floods occur.
The second reason is the unfavourable natural conditions . Ho Chi Minh city is impacted by monsoon and tropical weather and tide from the Pacific Ocean. Every year, the rainfall pattern is quite high, from 1200-1900mm, mustering in the rainy season (90%), some event about 50-100mm within 1 - 1,5 hours. Besides, the surface of some areas in Ho Chi Minh is lower than sea level, so when there are tide flows with high amplitude (3,5-4m), the tide penetrates into the interior city thereby causing flooding. In the flood-tidal and heavy rainy days (in September, October, November and December), the city is flooded in large areas. Due to the climate change, in some recent years, the rainfall pattern is getting higher, if the sea level rise occurs - according to the warning of the WB (World Bank??) for Vietnam - then Ho Chi Minh city is facing very serious flooding. In addition, the uncontrolled and illegal above-ground water extraction makes the surface subside and also causes floods.
Urban flooding in Ho Chi Minh city has very serious impacts on transportation: traffic jams happen quite normally in the rainy season because of flooding. Flooding disperses the wastewater from sewerage everywhere, which causes water pollution, epidemic diseases, damage to houses and instruments. Flooding by tide also causes salinity intrusion, which damages the crops and plants.
To measure the impacts, in this paper, GIS is used as a tool to analyse and assess flooding in Ho Chi Minh city. GIS supplies inputs for hydro-modelling and uses outputs from modelling to analyse and calculate the impact of flooding on other factors.