Disaggregation of Future Regional Climate Model Data to Generate Future Rainfall Intensity-Duration-Frequency Curves to Assess Climate Change Impacts

Abstract

Heavy increase in urbanization, industrialization and population is\ncausing an increase in emissions of greenhouse gases (GHG) and this\ncauses variations in atmosphere. Climate change causes extreme rainfall\nevents and these events are expected to be enhanced in the future. Since\nflooding is influencing urban areas, controlling and management of\nflooding is a major necessity. Intensity-Duration-Frequency (IDF) curves\nplay a huge role in representing rainfall characteristics by linking\nintensity, duration, and frequency of rainfall. Analysing short-duration\nrainfall is crucial for urban areas due to fast responses of drainage\nsystems against heavy rainfall events. IDF curves were generated via the\nGumbel method for rainfalls from 5-min to 24-h in this study. However,\nproviding short-duration rainfall data is challenging due to the low\ncapacity, costs and geographic conditions. Therefore, the HYETOS\ndisaggregation model was applied to obtain sub-hourly data. IDF curves\nare stationary since they only consider historical events. However, IDF\ncurves must be non-stationary and time varying based on preparation for\nupcoming extreme events. This study aims to generate IDF curves under\nclimate change scenarios. The Regional Climate Model (RCM) HadGEM2-ES\ngenerated under Representative Concentration Pathways (RCP) 4.5 and 8.5\nscenarios and was used in the study to represent future rainfalls.\nFuture daily rainfalls were disaggregated into sub-hourly using\ndisaggregation parameters of corresponding station’s historical rainfall\ndata since it is impossible to estimate parameters when hourly data is\nnot available. With this new approach, future daily rainfall data is\ndisaggregated into 5-min data by complying with historical rainfall\npatterns rather than complying with randomly selected rainfall\ncharacteristics. The study concluded that future rainfall intensities\nincreases compared to historical IDF curves. RCP8.5 scenarios have\nhigher rainfall intensities for all return periods compared to RCP4.5\nscenarios for all stations except a station. In addition, the accuracy\nof the selected disaggregation model was verified.