Landslide Susceptibility Screening Using Wind-Driven Rainfall

Rainfall is one of the most significant triggering factors for shallow landslides, raveling, and erosion of over-steepened slopes, especially in steeply inclined mountainous regions, such as the western Greater Himalayan Mountains of northern Pakistan. The influence of wind-driven rainfall is usually neglected in comparisons between rainfall and mass wasting. Wind-driven rain falls with an angle of incidence influenced by prevailing wind direction and velocity. The need to include considerations of incident rainfall distribution with respect to mass wasting processes is long overdue. The idea of coupling "wind-driven" rainfall based on directional monsoon with regional topography (slope aspect) was analyzed to ascertain the actual distribution of rainfall upon slopes exhibiting varying inclinations and slope aspect. Regional-level landslide susceptibility maps were prepared for the entire Indus River watershed using widely accepted methods including GIS heuristic weighted overlay and fuzzy logic techniques by including traditional rainfall distribution maps as one of the triggering factors. The results of that analysis were then compared with current research to examine whether an oblique/inclined rainfall correction map would aid in assessing landslide susceptibility by considering the impacts of slope inclination and aspect on the effective rainfall being "caught" by those slopes facing the prevailing wind directions. The susceptibility maps produced by this method were found to be more reasonable than others yet produced of such a large study area (similar to 75,000 km(2)).