Comment on nhess-2022-76

Abstract

During the last few decades, many researchers have produced landslide susceptibility maps using different techniques and models including the information value method, which qualified as a wide applied statistical model in several coastal environments. The aim of this study was to evaluate the susceptibility for the occurrence of landslides in Essaouira coastal area using this bivariate statistical method. In this coastal area were identified, inventoried and mapped 588 landslides, of different types, mostly from the observation and interpretation of different data sources, namely high-resolution satellite images, aerial photographs, topographic maps, and extensive field surveys. The rocky coastal system of Essaouira is located in the middle part of Morocco Atlantic coastal area. The study area was split into 1534 cliff terrain units of 50 m width. For training and validation purposes the landslide inventory was divided into two independent groups: training (70 %) and for validating (30 %). Twenty-two layers of landslide-conditioning factors were prepared, including: elevation, slope angle, slope aspect, plan curvature, profile curvature, cliff height, topographic wetness index, topographic position index, slope over area ratio, solar radiation, presence of faulting, lithological units, toe lithology, presence and type of cliff toe protection, layer tilt, rainfall, streams, land-use patterns, NDVI, lithological material grain size, and presence of springs. The statistical relationship between the conditioning factors and the different types of landslides were calculated using the bivariate information value method, in a pixel and in elementary terrain units base model. Validation of the coastal landside susceptibility maps was done using the landslide training group partitions. The ROC curves and Area Under the Curve were used to assess the accuracy and prediction capacity of the different coastal landslide susceptibility models. Two methodologies were adopted to evaluate coastal landslide susceptibility, one considering a pixel base approach and another one using coastal terrain units. The resulted coastal landslide susceptibility maps allowed classifying 38 % of the rocky coast subsystem with high susceptibility to landslides, being the majority of these high susceptible areas located in the southern part of the Essaouira coastal area. Those susceptibility maps would be useful for general planned development activities in the future as well as for environmental protection.