Abstract
Abstract. Due to the Central Mountain Range with an elevation up to about 4 km, the amount and distribution of rainfall in Taiwan associated with typhoons or tropical cyclones (TCs) depends not only on the distribution of convection within the TCs (internal structure) and influences from monsoon-scale environmental flow, but also on the orographic effect. This study analyzes the spatial and temporal characteristics of rainfall associated with 62 TC cases that affected Taiwan by using observations from the 371 automatic rain stations available in the period 1989–2002. It is found from the climatology maps that highly different rainfall distributions occurred for TCs that approached the Taiwan area from different directions. By performing objective clustering analysis of the rainfall time series of all the rain gauges, several characteristic temporal rainfall profiles are obtained. The geographic distribution of rain gauges that possess a particular temporal profile is also consistent with the possible TC track types that bring maximum rain to the Taiwan area at different times. Based on data in the 1989–2002 period, the development of a TC rainfall climatology-persistence (CLIPER) model is described. CLIPER is an optimized combination of climatology and persistence with different relative weighting for different forecast periods. Independent cases (other than the model development database) during 2003–2004 are used to validate the model. Objective measures like equitable threat score and bias score show that CLIPER's skill is acceptable for practical applications for 24-h rain threshold below 100 mm. However, the underestimation bias for more heavy rainfall is serious and CLIPER seems to have better performance for the northwestern Taiwan than for the other locations. Future directions for improvement of the CLIPER model are discussed.
Highlights
Impact from typhoons or tropical cyclones (TCs) is one of the major natural hazards to the coastal cities in Southeast Asia and in particular to Taiwan
The characteristics of TC rainfall in the Taiwan area is studied through various statistical analyses of data in the period 1989–2002 from the 371 automatic rain gauges on the island
Of occurrence of rain maximum are identified based on objective clustering analysis. These temporal profiles have a particular geographic distribution that should be determined by the different impact directions of the TCs
Summary
Impact from typhoons or tropical cyclones (TCs) is one of the major natural hazards to the coastal cities in Southeast Asia and in particular to Taiwan. The fact that the distributions of convection and rainfall in TCs have certain characteristic patterns both when they are over open oceans (Lonfat et al, 2004) and when making landfall (Chan et al, 2004) allows the application of statistical descriptions and predictions based on climatology. The purpose of this study is to provide a detailed statistical analysis of the characteristics of TC-related rainfall in the Taiwan area and illustrate the skill level of a simple climatology-based statistical model for 3000 m 2500 m 2000 m 1500 m 1000 m 500 m 200 m 0 m. The rain stations if the accumulated rain of the problematic station is zero or are quite uniformly distributed in the plain area but are less very low, the station in that particular TC period is treated as dense in the Central Mountain Range (CMR). Care is taken to compare data from stations at different altitudes because orographic effect sometimes generates rain in a mountainous area but not in a nearby plain area
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