University of Twente Student Theses


Developing a worst-case Tropical Cyclone rainfall scenario for flood on Dominica

Serere, Helen Ngonidzashe (2020) Developing a worst-case Tropical Cyclone rainfall scenario for flood on Dominica.

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Abstract:Fresh water flooding as a result of tropical cyclone rainfall depicts a hydrometeorological hazard that needs to be prepared against. When not adequately prepared for, freshwater flooding results in immense damages that disrupts economies, displace settlements, and increase the poverty line. To prepare and mitigate against tropical cyclone (TC) induced freshwater flooding, countries make use of design storms. One disadvantage, however, is that design storms are very different from actual storm events with respect to both spatial and temporal rainfall structures. Design storms tend to lose vital storm information which influences the results of the simulated flood hazards. When dealing with extreme rainfall events, the simplification of storm traits by design storm may result in major implications on the decisions made for flood mitigations owing to the differences in simulated flood characteristics between the design storm and the extreme rainfall event. This research intended to evaluate the flood implications of simulating a worst-case tropical cyclone rainfall scenario against a design storm of comparable rainfall characteristics. Using the Southern catchments of Dominica as a study area and the 2017 Atlantic basin TC Maria as a proof of concept, the research was carried out in two main steps. First a method was developed to extract extreme rainfall pixels from the passage of a TC given temporal layers of precipitation images. Using the extracted extreme rainfall pixels and Dominica’s 100-year design storm, flood characteristics of the TC scenarios and the design storm were compared. Based on the flood characteristics of the worst-case rainfall scenario (extreme TC rainfall pixel with the highest simulated flood characteristics) and the 100-year design storm, economic flood implications of simulating a flood from the two approaches are evaluated. Contrary to common perception, the results of the analysis showed the extreme rainfall pixels of TC Maria to result from a category 2 and 3 cyclones. Of the extreme TC rainfall pixels used as TC scenarios, the worst-case rainfall scenario resulted from a high intensity pixel with a maximum intensity of 107mm/hr, three peak intensity values, and a shortest distance from the TC eye of 10km. Comparisons made between the flood characteristics of the TC scenarios and the 100-year design storm showed the 100-year design storm to have overall shorter flood start times, higher flood volume, larger flooded areas and higher flood heights in comparison to the TC scenarios. Based on the obtained flood characteristics, the 100-year design storm was concluded to simulate overestimated flood characteristics which would imply overestimated flood mitigation measures.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Spatial Engineering MSc (60962)
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