Author(s): Yixiao Chen; Fang Yenn Teo; Andy Chan; Soon Yee Wong
Linked Author(s):
Keywords: No Keywords
Abstract: On September 2023, an extreme rainfall event occurred over Hong Kong and Pearl River Delta, which broke the hourly rainfall record since 1884 and resulted in a severe flood with significant socio- economical and financial losses. This event is considered to be highly related to the residual low-pressure trough from the Typhoon Haikui. Haikui made landfall at Fujian, China on 5th September. It continued travelling westwards and stayed over Pearl River Delta region. The remaining low-pressure system interacted with Southwest monsoon, resulted in the extreme rainfall event from 7 to 8th September. The aim of the present work is to conduct sensitivity study on numerical simulation model for better understanding on the climatological condition that led to this event. Weather Research & Forecasting Model (WRF) was used to conduct the numerical simulation for the extreme rainfall event. The study period is from 7th to 8th September 2023 with 2 days spin-up. The horizontal model resolution was set as 27 km and 9 km for outer and inner domain. The meteorological initial and boundary conditions were taken from the National Centers for Environmental Prediction FiNaL reanalysis (NCEP-FNL) data. Sensitivity study on microphysics scheme was conducted between Purdue Lin, Morrison-2-moment, Thompson and WSM6. Other physical parameterisation schemes were kept constant throughout the experiment. The results showed that Thompson performs better in producing the peak rainfall intensity among four simulations, followed by WSM6 over both stations. Over Sha Tin station, Thompson is able to simulate the pattern with two precipitation peaks on UCT 7th and 8th September, but the first peak was 5 hours earlier than observation with less rainfall between the two peaks. Similar to the Kwun Tong station, Thompson is able to simulate the peak intensity at the beginning and ending stage of the rainfall event but fail to maintain the intensity in between. WSM6 produces rainfall pattern during extreme rainfall period, however, the intensity is largely underestimated. Thompson scheme shows better performance in simulating the peak intensity than the other three schemes, however fail to reproduce the temporal variation. More improvement can be done by considering more sensitivity study on other physical parameterisation schemes and also running simulation with finer resolution.
Year: 2024