臺灣西部不同環境條件之集水區誘發崩塌的降雨條件分析

Abstract

降雨是引發崩塌災害的主要因素之一。台灣地形特徵複雜且地勢陡峭加上地處亞熱帶氣候，氣候多變且降雨充沛，這些因素與人為過度開發的綜合影響，使得台灣非常容易發生崩塌災害事件。若我們能充分了解各集水區降雨所誘發的崩塌條件，並進一步提高預警效果，就能減緩崩塌災害對我們所帶來的衝擊。 然而為了確定台灣不同地區的降雨條件是否會對崩塌程度造成差異，本研究分別選擇台灣西部由北至南從石門水庫及水區、大甲溪集水區、濁水溪集水區、曾文水庫集水區、高屏溪集水區，共五個集水區做為代表，並參考氣候變遷災害調適平台統計六項極端降雨指標，選取2004-2019年間10場具代表性的颱風作為降雨條件，利用數值模式(TRIGRS)進行分析。根據降雨與崩塌特性關係，通過皮爾森矩陣分析各個集水區的最大小時降雨量、地質特徵、及颱風路徑對崩塌結果的影響。 結果顯示，石門水庫及水區與高屏溪集水區主要受最大48小時降雨量影響；大甲溪集水區以累積降雨量為主；濁水溪集水區以最大24小時降雨量為主控因素；曾文水庫集水區則以最大12小時降雨量為主要降雨條件。崩塌多發生於坡度150至300之間，且在臺灣西部地區，由於降雨條件的影響，崩塌多發生於受長時間日曬、受較多降雨的坡向或順向坡坡上；高程介於1000m至2000m之間的地區最容易發生崩塌事件。研究進一步討論大甲溪流域次集水區降雨誘發崩塌的結果，確認最主要誘發崩塌的因素為高程，最大小時降雨量會隨著高程降低而縮短；而颱風路徑的差異會對北、中、南部造成不同降雨量與崩塌情況。 了解各個集水區不同的降雨條件特性，有助於幫助我們在災害預警中更加因地制宜，並能在災害來臨時及時應對，做出更有效的判斷，最大程度地保障人民生命財產安全。

Rainfall is one of the primary factors triggering landslide disasters. Taiwan's complex terrain, steep topography, subtropical climate, and variable precipitation make it highly susceptible to such events, exacerbated by human-induced overdevelopment. Understanding the specific rainfall-induced landslide conditions in various watersheds and enhancing early warning systems are crucial to mitigating the impact of landslides. To determine whether rainfall conditions vary in their impact on landslide severity across different regions of Taiwan, this study selected five representative watersheds from north to south: Shimen Reservoir and watershed, Dajia River watershed, Zhuoshui River watershed, Zengwun Reservoir watershed, and Kaoping River watershed. Utilizing statistical data from the Climate Change Adaptation Platform on six extreme rainfall indices and selecting 10 representative typhoons between 2004 and 2019, the study employed the TRIGRS numerical model for analysis. Based on the relationship between rainfall and landslide characteristics, Pearson correlation matrices were used to analyze the effects of maximum 48-hour rainfall, geological features, and typhoon paths on landslide outcomes in each watershed. The results indicate that Shimen Reservoir and Kaoping River watersheds are primarily influenced by maximum 48-hour rainfall; Dajia River watershed is predominantly affected by cumulative rainfall; Zhuoshui River watershed is controlled by maximum 24-hour rainfall; and Zengwun Reservoir watershed is mainly influenced by maximum 12-hour rainfall. Landslides occur most frequently on slopes with gradients between 15° and 30°, especially on aspects exposed to prolonged sunlight or receiving higher rainfall in Taiwan's western regions. Areas at elevations between 1000m and 2000m are particularly susceptible to landslides. Furthermore, the study discusses the results of rainfall-induced landslides in the sub-watersheds of the Dajia River basin, confirming that elevation is the primary triggering factor, with the duration of maximum hourly rainfall decreasing with lower elevations. Variations in typhoon paths lead to different rainfall amounts and landslide conditions in northern, central, and southern Taiwan. Understanding the unique rainfall conditions of each watershed facilitates tailored disaster preparedness and timely response strategies, ensuring the safety of lives and properties to the greatest extent possible during disasters.