The effect of forest fire on mass movement in Lebanese mountainous areas

Abstract

Mass movements are major hazards that threaten natural and human environments. In Lebanon, the occurrence of mass movements increased by almost 60% between 1956 and 2008. Forest fire has emerged as an additional hazard: it destroyed over 25% of Lebanon’s forests in a period less than 40 years. This paper investigates the potential effect of forest fire on the occurrence of mass movements in the Damour and Nahr Ibrahim watersheds of Lebanon. Mass movement and forest fire inventory maps were produced through remote sensing using aerial and satellite images. Forest fire was included as an additional factor in mass movement induction, and its effect was quantified from Landsat images through the normalised burn ratio (NBR) index. A field study was conducted to substantiate the mass movement inventory and NBR maps. Following the standardisation of the effect factors into layers using geographic information systems, the weight factor of each layer for inducing mass movements was evaluated using the modified InfoVal method, and a mass movement susceptibility map was generated. Exceeded only by changes in land cover, the NBR produced the highest weights, making forest fire burn severity the second highest factor influencing mass movement occurrence in the study areas.