Abstract
Abstract. This study is focused on the modification of a typhoon rainfall climatological model, by using the dataset up to 2006 and including data collected from rain gauge stations established after the 921 earthquake (1999). Subsequently, the climatology rainfall models for westward- and northward-moving typhoons are established by using the typhoon track classification from the Central Weather Bureau. These models are also evaluated and examined using dependent cases collected between 1989 and 2006 and independent cases collected from 2007 to 2011. For the dependent cases, the average total rainfall at all rain gauge stations forecasted using the climatology rainfall models for westward- (W-TRCM12) and northward-moving (N-TRCM12) typhoons is superior to that obtained using the original climatological model (TRCM06). Model W-TRCM12 significantly improves the precipitation underestimation of model TRCM06. The independent cases show that model W-TRCM12 provides better accumulated rainfall forecasts and distributions than model TRCM06. A climatological model for accompanied northeastern monsoons (A-TRCM12) for special typhoon types has also been established. The current A-TRCM12 model only contains five historical cases and various typhoon combinations can cause precipitation in different regions. Therefore, precipitation is likely to be significantly overestimated and high false alarm ratios are likely to occur in specific regions. For example, model A-TRCM12 significantly overestimates the rainfall forecast for Typhoon Mitag, an independent case from 2007. However, it has a higher probability of detection than model TRCM06. From a disaster prevention perspective, a high probability of detection is much more important than a high false alarm ratio. The modified models can contribute significantly to operational forecast.
Highlights
The island of Taiwan is situated on one of the main western North Pacific typhoon paths
All typhoons that affected Taiwan between 1989 and 2006 are classified using the typhoon track classification created by the Central Weather Bureau (CWB) to establish climatological rainfall models for westward- (WTRCM12) and northward-moving (N-TRCM12) typhoons
Five typhoons accompanied by monsoons are selected to develop accompanied climatological rainfall models (ATRCM12)
Summary
The island of Taiwan is situated on one of the main western North Pacific typhoon paths. Chu and Chen (1988) analyzed the precipitation features of six typhoons accompanied by northeastern monsoons and found that these types of typhoons are likely to form three major rainfall centers in northern Taiwan: the Datun mountainous areas (Zhuzihu, Station E in Fig. 1); the area between Wudu (Station F) and Huoshaoliao (Station G); and the western mountainous areas of the Lanyang Plain. The available historical data (1989 to 2006) include five typhoons accompanied by northeastern monsoons These five cases are selected to establish a climatological rainfall model for typhoons accompanied by northeastern monsoons (A-TRCM12). Forecast rainfall from TRCM06 is calculated and compared to forecasts from A TRCM12 These forecasts are validated using actual rainfall data to better understand how classifying typhoons according to their tracks or unique environmental effects improves climatological models.
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