A Spatiotemporal hydrological response of extreme urban floods in Ha Noi – Vietnam.

Urban flood mostly is pluvial flood, caused by high rainfall intensities combined with the unsuitable drainage system and land cover. Because of the heterogeneous drainage system and the storm distribution dynamics, urban floods are rapid and spontaneous in space and time. Flood risk analysis was created to understand and assess the flood behavior, manage and mitigate the flood damage. However, flood risk assessments recently only have focused on the spatial distribution of the flood while temporal flood evolution in urban area is still an open question. This research aims to provide a spatio-temporal analysis of the urban flood by implementing the simplified model-based representation of flood evolution/development in space and time (spatiotemporal patterns) including time to flood the manhole, the location, spatial and temporal sequences of flood.To specify, 3 precipitation distribution patterns were collected from rainfall incidents in 2008, 2019, 2020, then extrapolated to create 21 scenarios following the return periods (i.e. 1.25-year, 2-year, 2.5-year, 5-year, 10-year, 20-year, 50-year). In each scenario, the dynamics of flood was estimated using the urban drainage system by SWMM5. Case study (Do Lo, Yen Nghia, Ha Dong, Ha Noi, Viet Nam) was divided into 115 sub-catchtments based on the Digital Elevation Model (DEM) and the drainage system map of this area. Land cover was created based on the LANDSAT images. Domestic waste water distribution was included in the model. The model is validated with the extreme events in 2020 and 2022.A spatio-temporal risk map was generated to show the flooding spatio-temporal sequences and non-flood region. Flood evolution on the time scale was shown in this map. The rate of flood change diagrams shows the flood responses from urban areas which vary from 1 to 107 mins in different scenarios.Rain gauge distribution sensitivity is examined under ranges of rain gauge distribution combinations in term of space and time.