**1. Introduction**

Landslides are a common geologic hazard in the hill and mountain terrains of the world. The landslides impact the society and livelihoods of the affected communities. Landslides can result in loss of lives and cause potential damage to infrastructure facilities, agricultural land, public and private assets. UNESCO has also recognized landslides as a significant geohazard globally and attributes 14% of total casualties from various natural hazards like earthquakes, floods, etc. to landslides [1,2]. Global landslides cause nearly 1000 fatalities and a loss of approximately 4 million USD in a year [3]. They can impede the region's economic growth and development and hamper the region's social set-up by isolating the hill communities for long periods from the rest of the surrounding areas. Landslides also lead to environmental degradation by the removal of soil and tree cover. They have significant economic value and affect the environment adversely and hence are a severe concern in mountainous terrains. Assessment of the regions prone to landslides is therefore mandatory for any developmental, land use, and mitigation planning in the hill and mountain communities.

Landslides have profound social and economic impacts. Landslides affect public and private properties and cause both direct and indirect losses that can have either consequential or inconsequential economic impacts [4]. Linear infrastructure like roads or railroads are often severely damaged by landslides causing disruption to normal traffic or completely

**Citation:** Sujatha, E.R.; Sridhar, V. Landslide Susceptibility Analysis: A Logistic Regression Model Case Study in Coonoor, India. *Hydrology* **2021**, *8*, 41. https://doi.org/10.3390/ hydrology8010041

Academic Editor: Tamim Younos

Received: 29 January 2021 Accepted: 3 March 2021 Published: 5 March 2021

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cutting off the access to the affected areas. This directly affects the tourism industry in the region. The direct economic impact which is consequential involves the repair of damaged infrastructure which includes property and installations or its replacement and clean-up activities. Fatal and non-fatal injuries or accident costs caused by landslide also fall under this category. In cases of remote hamlets or villages, whose economy depends on transporting their raw material or manufactured goods using the roads affected by landslides suffer economic losses due to traffic disruption caused by landslides, though indirect losses are consequential [4]. Moreover, the decrease in tourist activity due to landslides or even landslide vulnerability is an indirect consequential loss. Indirect losses also include reduced real estate values, devaluation of tax revenues, loss of industrial/agriculture revenue, loss of productivity of labor force due to injury, death, or trauma caused by landslides, and the capital spent on prevention/mitigation measures [5]. Landslides can significantly reduce the revenue of the affected regions causing a social set-back [6]. They impose severe constraints to the affected population in terms of economic loss and social set-back [7]. This significant impact of landslides on the socio-economic system of the affected region mandates a thorough understanding of factors causing landslides in the specific geo-environment.

Landslides are caused by several topographical, environmental, geological, hydrological, and geotechnical factors such as terrain features, slope morphometry, drainage pattern, land use and land cover in the region, geomorphological set-up, etc. These factors are usually termed as causative factors [8,9]. Landslides are triggered by extreme rainfall events or snowmelt, seismic activity, and/or anthropogenic activities [2,10]. Climate change and extreme rainfall events trigger landslides more frequently, causing considerable losses to the society, particularly in areas with a large settlement [11–14]. Haque et al. [15] investigated the human cost of global warming, focusing on deadly landslides and triggers between 1995–2014. They reported that there was a significant increase in the number of fatal landslides in the said period. Haque et al. [15] also demonstrated the linkage between catastrophic landslides and extreme rainfall events in their study, particularly in densely populated areas. The effect of various factors contributing to landslides in a region can be perceived in a landslide susceptibility map that describes the spatial propensity of landslide vulnerability in a selected geographic or geomorphic boundary.

Landslide susceptibility assessment is a complex process and involves determining the spatial association between various factors causing landslides and its location. Several statistical, deterministic, and heuristic methods are employed to evaluate landslide susceptibility [13,15–24]. Data-driven statistical models are widely favored for their simplicity and ease of application, while the limitations can come from a lack of local data including temperature and precipitation [25]. Popular statistical methods used to assess landslide susceptibility are bivariate methods [26,27], multivariate regression [28,29], and logistic regression [19,20,30–32]. Bivariate models like frequency ratio, weights of evidence, information value, and yule coefficient assess the spatial association between landslide occurrence and each causative factor using a set of observations. Bivariate models are simple and straightforward, but the relative importance of the factors influencing landslides cannot be determined using bivariate methods. Multiple regression models attempt to evaluate the relationship between landslides and numerous causative factors. They also estimate the importance of these factors in causing landslides and can also identify outliers. However, the multiple regression model's success depends on the data used, and the results are too difficult to interpret. Logistic Regression is a statistical modelling approach used to parameterize a non-linear relationship between dependent and independent variables [31,33,34], particularly when the dependent variable has a binary or dichotomous output. Logistic regression, like linear regression, evaluates the relationship between several predictor variables and the dependent variable. Unlike linear regression, which requires continuous variables, logistic regression can use any type of independent variables—continuous and categorical. It is also not mandatory for independent variables to have a normal distribution and evaluate multiple independent variables. The logistic

regression model features make it an ideal choice for modelling landslide susceptibility in this study. However, it should be noted that this method requires a large dataset and is sensitive to the large variance in the dataset used.

Landslide susceptibility models are region-specific and are, to a large extent, dictated by the local geo-environmental set-up.

Coonoor is a popular hill-station in Tamil Nadu, India and is located in the western ghats, a zone prone to intense slope stability problems. Tourism and tourism-related activities such as flower shows, vegetable shows, hiking, special events in botanical gardens, eco-tourism, etc. are prevalent throughout the year. People witness landslides every year, particularly in the months between October and December due to intense and prolonged monsoonal rainfall. These landslides cause severe distress to the hill community in terms of social and economic losses [10]. Therefore, it is necessary to study the factors causing landslides in the Coonoor Taluk to map the regions susceptible to landslides.

This study evaluates the factors that contribute to landslide occurrences, understands their spatial association with the landslide, and map landslide susceptibility using a logistic regression model for Coonoor Taluk, India. The objective of the study is to throw light on the relation between landslide susceptibility and anthropogenic activities in this region. Geo-environmental factors are used to build the landslide susceptibility map and are compared with the most significant anthropogenic activities that have modified the natural setting in the region.
