Figure 9. Relationship between potential maximum retention and SY during a typhoon event.
The observational data showed that the two parameters would exhibit different functional relations under different cumulative rainfall conditions. The functional relationships could be divided into three types according to the cumulative rainfall value, namely Type I—cumulative rainfall value < the invoked value of SY; Type II—cumulative rainfall value > the invoked value of SY, which was classified as low cumulative rainfall (SY = 473.64S–0.866); and Type III was classified as high cumulative rainfall (SY = 13764S–1.133).
Table 2 lists the applicable functions for expressing the relationship between cumulative rainfall and SY recorded in typhoon events during 1999–2009. According to the data, Type I cumulative rainfall was < 197.2 mm, and typhoon events classified into this category were Maggie (June 1999), Soudelor (June 2003), Nanmadol (December 2004), Longwang (September 2005), and Parma (October 2009). Type II covered the range from 197.2 to 754.4 mm, and corresponding typhoon events were Bilis (June 1999), Haitang (July 2005), Bilis (July 2006), Sepat (August 2007), Krosa (October 2007), Kalmaegi (July 2008), and Fung-Wong (July 2008). Type III covered the range from 754.4 to 1419.7 mm, with the corresponding typhoon events being Mindulle (June 2004), Sinlaku (September 2008), and Morakot (August 2009).
Table 2. Cumulative rainfall in typhoon events and applicable functions.