應用雷射雨滴譜儀修正臺灣地區降雨動能參數之可行性研究-以屏東地區為例

臺灣目前所使用的降雨動能公式為Wischmeier and Smith(1958)根據Laws and Parsons(1943)於美國華盛頓地區量測之降雨資料所建立，其公式為一經驗公式，由於經驗公式具有地域性，不適合應用於自然環境與發展程度不同的區域；且臺灣地區的降雨及氣候型態與美國大不相同，除此之外，量測方法使得相關參數精度有不足之情況，可能使得公式推估結果之精度較低，亦會導致降雨動能有高估或低估之情形。因此，本研究為瞭解降雨動能經驗公式(Wischmeier and Smith)對臺灣地區之影響，以屏東地區為研究區域，於屏東科技大學氣象站內架設雷射雨滴譜儀(OTT Parsivel2)，蒐集2017年1月至2020年12月每五分鐘之雨滴譜資料，利用雷射雨滴譜儀所量測之雨滴譜資料進行屏東地區之降雨特性分析，並修正臺灣目前所使用之降雨動能參數，建立適用於屏東地區之降雨動能參數公式，進而提供更有效應用於計算降雨沖蝕指數之參考。根據Wischmeier and Smith(1978)對有效雨場之定義，分割有效降雨事件共計120場，分析結果顯示，估算降雨動能有85 %數據高於實測降雨動能，而物理降雨動能有99.9 %數據低於實測降雨動能，表示屏東地區目前使用的降雨動能有高估之情形。在單位降雨動能和降雨強度回歸關係的部分，以屏東地區為例，在降雨強度於53 mm/hr時有臨界值，小於53 mm/hr時適用單位降雨動能e=0.0671log(I)+0.0996，判定係數 (R2) 為0.36；大於53 mm/hr時適用單位降雨動能e=0.0003(I)+0.2017，判定係數(R2)為0.03；最大30分鐘降雨強度(I30max)與降雨沖蝕指數(R)回歸關係部分，R=0.819(I30max)1.6799，判定係數(R2)為0.83。綜觀上述，本研究藉由雷射雨滴譜儀量測雨滴譜資料，利用儀器蒐集到之雨滴譜資料加以分析及探討，且建立屏東地區之單位降雨動能公式，可以用作未來降雨動能計算及降雨沖蝕指數推估之參考，以供水土保持相關研究及估算之依據。

關鍵字

雷射雨滴譜儀；雨滴譜；降雨動能；降雨沖蝕指數

並列摘要

Currently, Taiwan’s unit rainfall kinetic formula was developed by Wischmeier and Smith(1958) based upon Laws and Parson’s(1943) rainfall data, in Washington, United States. The formula is an empirical formula , so it is not suitable for application due to its regional. In areas where the natural environment and the developed area are different, the rainfall patterns and climatic type in Taiwan are different from those in the United States. In addition, the measurement method makes the parameters, which may make the accuracy of the formula calculation results, which will cause rainfall energy to have an error. In order to understand the impact of the empirical formula of rainfall kinetic energy (Wischmeier and Smith) in Taiwan. This study chose the Pingtung County region as the research area and set up a laser raindrops spectrometer (OTT Parsivel2) in the weather station of Pingtung University of Science and Technology. The data were measured from January,2017 to December,2020, the rain droplet size spectrum every five minutes, using the rain droplet size spectrum measured by the laser raindrops spectrometer to analyze the rainfall characteristics of Pingtung County, and modify the rainfall kinetic energy parameters used in Taiwan to establish and apply the formula of unit rainfall kinetic energy in Pingtung County provides a more effective reference for calculating rainfall erosion index. According to the definition of effective rainfall events calculated by Wischmeier and Smith (1958), there are 120 effective rainfall events. The results show that 85 % of the estimated rainfall kinetic energy is higher than the measured rainfall kinetic energy, and 99.9 % of the physical rainfall kinetic energy is lower than the measured rainfall kinetic energy, which means that the rainfall kinetic energy is used to error in Taiwan. For the regression relationship between unit rainfall kinetic energy(e) and rainfall intensity(I), taking Pingtung County as an example, there is a critical value when the rainfall intensity is 53 mm/hr. When the rainfall intensity is below 53 mm/hr,e=0.0671log(I)+0.0996,(R2=0.36) is applicable；when the rainfall intensity is above 53 mm/hr,e=0.0003(I)+0.2017,(R2=0.03) is applicable；the power regression relationship between the maximum 30-minutes rainfall intensity and the rainfall erosion index, R=0.819(I30max)1.6799,(R2=0.83). On the whole, this study uses the laser raindrops spectrometer to measure the rain droplet size spectrum datas, analyzes and discusses the raindrops spectrum datas collected by the instrument, and establishes the unit rainfall kinetic energy formula in Pingtung County, which can be used for future rainfall kinetic energy calculation and the reference for estimation of rainfall erosion index shall be the basis of research and estimation related to supply water and soil conservation.