The Seasonal Rainfall Characteristics over Taiwan in 2005 and the River-Runoff simulations by Three Typhoon-Induced Heavy Rainfall events

• Main Authors: Yu-yu Fu, 傅佑瑜
• Other Authors: Ming-Jen Yang
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/w9b6s7

碩士 === 國立中央大學 === 水文所 === 96 === Different precipitation events occur under different synoptic weather regimes, and they are strongly affected by the Taiwan terrain and large-scale/synoptic conditions, so it is difficult for the meteorological model to have accurate precipitation forecast. This thesis utilized analyzes the automatic rain gauge data of the Central Weather Bureau and WRF-simulated rainfall data provided by Mr. Shi-Chien Wang. 1) to investigate the rainfall characteristics for each weather regime, 2) to examine the predictability of seasonal-to-annual rainfall of the WRF model, and 3) to verify the accuracy of WRF-predicted rainfall at different time scales. The heavy rainfalls associated with typhoons often induce severe flooding, debris flows, landslides, and cause a great lose of human lives in Taiwan. Thus, in order to understand the flooding characteristics under typhoon-induced the heavy-rainfall events, this study will uses the FLO-2D hydrological model to simulate the river discharge over the Shihmen Reservoir watershed for three typhoon events in 2005. Results show that the WRF model simulates better the distribution of seasonal rainfall than that for individual event (Mei-Yu front and typhoon), because the WRF model has a good skill at predicting the orographic rainfall under the prevailing wind in different seasons. This study also discusses the effects for the rainfall increase over the windward slopes and the decrease over the leesides in Taiwan. We find that the WRF model predicts well the rainfall distribution and typhoon tracks for heavy rainfall events, but the WRF model tends to over-predict the precipitation amount. If the WRF-simulated rainfall is taken as input for the FLO-2D hydrological model, the predicted river discharge is highly sensitive to the errors inherent in the WRF-simulated rainfall. Finally, the neglect of initial base flow and infiltration outflow in the FLO-2D model may cause discrepancy in discharge at the later stage of a flooding event.