Introduction

Environmental hazards are defined based on the process of human relationship with the environment. Otherwise, the phenomena we call danger. It is part of the normal and common behavior of nature. This process has been dominant in geography since ancient times, perhaps since the dominance of environmental determinism, and according to many geographers, it is considered the main axis of geographical activities. Therefore, environmental risks are always considered one of the most important issues in societies. Land degradation is one of the major problems in developing countries, mainly due to the misuse of soil resources and subsequent erosion. Mass movements, including landslides, are one of the most important issues in the field of natural hazards, because their occurrence can cause significant human and economic losses, especially in mountainous areas. One of the areas that is exposed to this risk is Nobaran Basinin Markazi Province, which is exposed to the risk of landslides due to its hydrogeomorphology and hydroclimatic conditions. For this reason, this study has focused on identifying areas prone to landslides.



Methodology

The present study is of an applied type and its research method is analytical based on the integration of data analysis, geographic information system, and the use of multi-criteria analysis techniques. In order to zone the landslide hazard, in the data collection stage, the influencing components must first be identified and the required data and information collected and classified based on them. For this purpose, in this study, the influencing factors (including: slope, geology, land use, rainfall, distance from the river, distance from the fault, slope direction, elevation classes and distance from communication routes) were first identified, taking into account the natural and human conditions of the region, reviewing the background of studies and consulting with scientific and local experts familiar with the region. Then, in the next step, information layers related to each of the factors were prepared in the geographic information system environment. The information layers of the waterway network were extracted using the map of rivers of Markazi province. The slope layers were also prepared using a 12.5 m digital elevation model downloaded from the site (vertex.daac.asf.alaska.edu, and the information layers related to lithology (rock resistance) and faults were prepared by digitizing from the geological map of the province; with a scale of 1: 100,000. To extract the land use of the study area, Landsat 8 sensor (OLI) images, obtained from the site (earthexplorer.usgs.gov), were used. In this regard, first, geometric and atmospheric corrections were performed on the images using the Flash method in Envi software. Then, classification was performed using the object-oriented method and the nearest neighbor algorithm in Ecognition Developer software, and the results of the classification of land uses in the present study, both in terms of individual land uses and in terms of the total accuracy and kappa statistics, have acceptable accuracy (greater than 85 percent) in relation to the information produced.





Results

According to the results obtained from the analysis of information related to the occurrence of landslides in the study area, it has been determined that the land use factor has had the greatest impact on the occurrence of landslides in the region. In such a way that the highest number of landslides have occurred in agricultural, orchard and pasture land uses. The least influential factor was the distance from the river with a weight of 0.011. The second factor that had the most influence on the occurrence of this hazard was the slope factor with a weight coefficient of 0.247. The important and influential parameters studied in this study are the slope factor with a weight of 0.191, the height classes with a weight of 0.147, the distance from the road with a weight of 0.087, the slope direction with a weight of 0.052, the distance from the fault with a weight of 0.031, and the precipitation with a weight of 0.012, respectively, which strengthen the potential for landslide hazard in Nobaran Basin. According to the zoning map of Nobaran Basin, it can be said that 417.11 km of the area of this county is in the very high-risk category, 400.33 km is in the high-risk category, 325.12 km is in the medium-risk category, and 217.710 km is in the very low-risk category. It can also be said that the results of this study indicate the high potential of Nobaran Basinin terms of landslide occurrence. Therefore, the high-risk areas determined in this study are lands where unprincipled works should not be carried out, such as destruction of vegetation cover due to conversion of pasture lands to crops and livestock pastures, quantitative and qualitative reduction of vegetation cover due to excessive grazing of livestock, rainfed cultivation on sloping lands, failure to observe crop rotation, and unprincipled construction and manipulation for road construction.

Conclusions

Nobaran Basin, Markazi Province, is very prone to landslides due to its geological, physiographic, lithological, climatic and human conditions. Accordingly, the aim of this study is to prioritize the factors affecting landslide occurrence and to zone the risk of its occurrence in Nobaran Basin, Markazi Province. In this study, using 9 parameters (elevation, slope, slope direction, lithology, distance from fault, distance from waterway, distance from communication routes, precipitation and land use) and the combined analytical network model (ANP) and ARAS model, landslide-prone areas in Nobaran Basinhave been identified. Based on the results obtained, the central and southeastern parts of the region have a high potential for landslides. According to the results of landslide risk zoning; 417.11 and 400.300 square kilometers of the area have very high and high risk, respectively. Finally, it can be said that the most important factor contributing to the increase in the amount and potential of landslides in Nobaran Basinis land use change and the increase in agricultural lands and livestock pastures.