Generating event-based landslide maps in a data-scarce Himalayan environment for estimating temporal and magnitude probabilities

Event-based landslide maps display landslide events of different magnitudes that are associated with a single major trigger. Event-based landslide maps allow the estimation of spatio-temporal probabilities of landslide events that are required for the assessment of landslide hazard. In this paper, we discuss the generation of event-based landslide inventory maps for a region in Darjeeling Himalayas (India) with limited historical landslide information. We used eight different sets of source data, spanning the period from 1968 to 2007, which include topographic maps, satellite images and post-event field maps. For each period we mapped the various landslide types, and calculated landslide density and activity in individual terrain units to analyze changes in the spatial behavior of landslides through time. For the assessment of the temporal landslide probability, we used landslide event-days and associated daily and antecedent rainfall amounts in a multivariate statistical analysis to model the temporal relationship between landslide events and the amount of triggering rainfall. For estimating the magnitude probability, we applied magnitude–frequency analysis for the different event-based landslide maps using landslide area (m2) as a proxy. Despite the incompleteness of the source data sets used, the resulting landslide inventory maps can be used successfully in determining temporal and magnitude probabilities of future landslides.