Review of approaches, applications and updating 1-hour and 2-hour probable maximum precipitation (PMP) estimates for Hong Kong

Abstract

A study of Probable Maximum Precipitation (PMP) methodology and its application has been carried out because PMP is a widely adopted approach for the calculation of maximized rainfall. The PMP estimates form a basis for further risk assessment, e.g. landslide risks, flood risks, etc. as to gauge the impact of rainstorms brought to Hong Kong.

In view of the extreme weather events and more complicated dam and reservoir designs in recent years, a regular update of the PMP estimates is increasingly important for the protection of lives and livelihood of the citizens.

The objective of the study was to update the 1-hour and 2-hour PMP estimates of Hong Kong. Last update covered the rainstorms from the period of 1955-1965 and 1985-2001. In this update, the period covered is extended to 2002-2014.

Data has been obtained from the 105-108 automatic rain gauges located at different parts of Hong Kong, by GEO and Hong Kong Observatory (HKO)

The data is presented in the form of PMP curves which show the rainfall depth against the areas covered of the top rainstorms, after moisture maximization.

It is concluded that the new 1-hour and 2-hour PMP estimates are higher than the previous estimates. This provides updated data inputs for further risk assessment by different government departments of Hong Kong.

This PMP study is premised on an expanded historical rainstorm database. The rainfall data of recent years show that there is increasing occurrence and intensity of extreme rainfall events in Hong Kong as compared to the past. This, to some extent, reflects the impact of climate changes in extreme rainfall.

In anticipation of more severe rainstorms due to climate changes, a regular update of PMP estimates as well as co-ordinated efforts of international community to address the issue would be of paramount importance in the years ahead.