A Climatology Model for Forecasting Typhoon Rainfall in Taiwan

Abstract

The continuous torrential rain associated with a typhoon often caused flood, landslide or debris flow, leading to serious damages to Taiwan. Thus, a usable scheme to forecast rainfall amount during a typhoon period is highly desired. An analysis using hourly rainfall amounts taken at 371 stations during 1989-2001 showed that the topographical lifting of typhoon circulation played an important role in producing heavier rainfall. A climatology model for typhoon rainfall, which considered the topographical lifting and the variations of rain rate with radius was then developed. The model could provide hourly rainfall at any station or any river basin for a given typhoon center. The cumulative rainfall along the forecasted typhoon track was also available. The results showed that the R 2 value between the model estimated and the observed cumulative rainfall during the typhoon period for the DanShui (DSH) and Kao-Ping (KPS) River Basins reached 0.70 and 0.81, respectively. The R 2 values decreased slightly to 0.69 and 0.73 if individual stations were considered. However, the values decreased significantly to 0.40 and 0.51 for 3-hourly rainfalls, indicating the strong influence of the transient features in producing the heavier rainfall. In addition, the climatology model can only provide the average conditions. The characteristics in individual typhoons should be considered when applying the model in real-time operation. For example, the model could give reasonable cumulative rainfall amount at DSH before Nakri (2002) made landfall on Taiwan, but overestimated the rainfall after Nakri made landfall and weakened with significant reduction in convection.

Characteristics of rainfall during tropical cyclone periods in Taiwan

“…3. The strategy used to construct the rainfall climatology here is based on Lee et al (2006) and different from that in Marks et al (2002) that developed the R-CLIPER for Atlantic TCs. The latest version of R-CLIPER utilizes rain estimates from the Tropical Rain Measurement Mission (TRMM) Microwave Imager (TMI) and derives storm-centered mean rain rate distribution stratified for different TC intensities.…”

“…However, when a typhoon is approaching the Taiwan Island, its structure and convection distribution will be greatly affected by Taiwan's topography and highly asymmetric rainfall distribution will likely occur. For example, Lee et al (2006) showed that the features of TC rainfall in the Taiwan area are closely locked by the topography. Therefore in developing the rainfall CLIPER model for the Taiwan area, the actual climatological rainfall map is used.…”

“…Sometimes, the difficulty in forecasting rainfall associated with TCs was further increased by the fact that heavy rainfall was brought by monsoonal flows enhanced or modified by the TC circulation. A recent example is Typhoon Mindulle (2004) that was accompanied by strong Asian summer monsoonal southwesterlies and resulted in large amount of rainfall in the southwest area of Taiwan (Lee et al, 2006). Therefore, improving the skill of rainfall prediction from the short range (1-12 h) up to 3 days becomes a major target for the Taiwan local forecasters and personnel in hazard mitigation organizations such as the National Science and Technology Center for Disaster Reduction (NCDR).…”

Multi-objective optimization of typhoon inundation forecast models with cross-site structures for a water-level gauging network by integrating ARMAX with a genetic algorithm

“…QPESUMS forecasts future rainfall patterns by predicting the movement paths of cloud cells. Data are provided for a wide range of applications, including typhoon rainfall forecasts (Lee et al, 2006), river flooding forecasts (Vieux et al, 2003), and landslide forecasts (Chen et al, 2007).…”

Parameter Automatic Calibration Approach for Neural-Network-Based Cyclonic Precipitation Forecast Models

“…Most typhoons in Taiwan form between May and November, and, on average, 3.9 typhoons affect Taiwan each year. As soon as a typhoon strikes, it often causes continuous torrential rainfall, leading to severe flooding, landslides, and debris flow [1]. Therefore, an effective and quantitative precipitation forecast model for typhoon periods is necessary.…”