Flood Risk in Vietnamese Coastal Cities – Remote Sensing Based Urban Structure Types as a Planning Relevant Tool

Coastal and delta cities in Vietnam like Ho Chi Minh City, Da Nang, or Hué are exposed to multi-hydrometeorological hazards caused by heavy rainfall, typhoons, tsunamis, rising sea levels, land subsidence as well as river flooding, intensified by global climate warming. Being exposed to these regular events, different degrees of spatial vulnerabilities are resulting for the citizens in relation to their distance to water ways or height above sea level, but also their capabilities to recover from possible hazards.

Since development of many Southeast Asian cities is extremely dynamic, city planners are lacking relevant planning information on population numbers and material flows (waste, drinking water demand, wastewater disposal, energy consumption, etc.), which are usually not provided by outdated masterplans. For that reason, so called Urban Structure Types (USTs) can be defined and derived from high-resolution remote sensing data. They are basic urban spatial units with homogeneous functional and morphological structure, delineated by shape, form, height, material, and density parameters. USTs are independent, quantifiable, and generic and thereby providing a surplus information to urban land cover classes. Their final classification is achieved by machine learning approaches applied to high and very high resolution imagery. A discrimination is made between globally applicable parameters like building height, size, or density and locally adjusted parameters like e. g. distance to water way or street width which are additionally required to cover the character of the individual cities.   

Urban Structure Types are a crucial input for hydrological modelling as well as damage modelling approaches, but they are also correlated with socio-economic data collected by questionnaires and interviews in several sampled quarters of the cities. As a conclusion, the USTs might indicate different ways of living within the city and give hints to consumption patterns but also topics of environmental justice.