Multi-geospatial flood hazard modelling for a large and complex river basin with data sparsity: a case study of the Lam River Basin, Vietnam

Mapping flood hazard becomes a basic and crucial requirement to cope with and to mitigate flood risks. However, it is a big challenge to accurately construct a flood hazard map in the large and sparsity data basin. Here, we present a new approach to make a flood hazard map in a large and complex river basin with data sparsity based on a comprehensive analysis of the relationship between previous flood records and hydrometeorological and geographical features coupled with holistic knowledge. The results show that the AHP-GIS approach (an integrated GIS-based Analytic Hierarchy Process method) can produce more accurate and reliable flood hazard map in basins with complex geological and hydrometeorological features such as the Lam River Basin (LRB). The LRB was a high vulnerability to flooding with approximately more than 90% of the total area in this river basin was classified into moderate, high, and very high hazard of flooding. More specifically, high, and very high flood hazard area occupied nearly 30% of the total area and affected nearly 45% of households living in the basin. More noticeable, these high flood hazard areas were in small valleys along the rivers and streams running from high mountains in the southwest to the coastal region. Moreover, the study indicated that rainfall and slope were the main factors that influence mapping flood hazard and assessing flood risk in the steep slope areas.