九九峰地區九二一地震崩塌植生指數變遷分析

Change Detection for Vegetation from Landslides of the 921 Earthquake at Mt. Jiujiufong with the NDVI Analysis

本研究主要蒐集九九峰地區1999年至2004年之SPOT衛星影像進行影像植生指數分析，以探討該地區九二一地震崩塌後植群逐年之變遷情形。本研究區以埔里事業區第8至20林班為研究分析範圍，由常態化差異植生指數（Normalized Difference Vegetation Index, NDVI）變遷分析結果，顯示九二一地震前植被覆蓋極為茂密，NDVI之平均值高達0.61，而地震後多數山頭崩落之土石大量堆積於局部溪谷坡腳，平均值劇降為0.37；地震後至桃芝颱風前為植被回復期，此近二年期間氣候較為穩定，植被逐漸回復覆蓋，2001年平均值已提高至0.54；桃芝颱風後至敏督利颱風後期間為變動期，此三年期間歷經桃芝與敏督利颱風挾帶豪雨之沖刷，植生指數則呈現變動情形。 Vegetation recovery at Mt. Jiujiufong after the 921 earthquake of 21 September 1999 in Taiwan wasinvestigated with the Normalized Difference Vegetation Index (NDVI) analysis. The time-series of sevenSPOT satellite images for a period between 1999 to 2004 for an area covered by the 8th to 20th forestcompartments in the Puli Working Circle were used. The results showed that the vegetation wasflourished with the NDVI value of 0.61 prior to the earthquake, the value reduced to 0.37 immediatelyafter the earthquake due to severe landslides. Then, the vegetation recovered gradually for nearly twoyears under stable weather conditions, and the NDVI value increased to 0.54 prior to Typhoon Toraji. Forthe three-year period between Typhoon Toraji of July 2001 and Typhoon Mindulle of July 2004, theNDVI values fluctuated widely with weather conditions at the mean value of 0.45, due to land erosionfrom rainfalls.