Assessing the impact of urban development on landslide susceptibility: a case of Shimla

Abstract

Landslides are one of the major destructive disasters in Shimla, causing loss of life, loss of livelihood, infrastructure damage, etc. Landslides increase every year due to increasing population and human activities. As per the Shimla Development Plan, Shimla was planned for a population of 25,000. However, post-independence, the rapid population growth exceeded the decided population. The increasing population, along with the tourists, increases the pressure and makes the city more vulnerable. Urban development is making the city develop, but more vulnerable to landslides. The study aims to assess the impact of urban development on landslide susceptibility, with key objectives to identify the urbanization changes over time and to identify vulnerable areas by conducting a landslide susceptibility analysis. Landslide susceptibility analysis is conducted to analyse how the susceptibility has increased with the increase in urban development. GIS-based spatial analysis, statistical methods, and historical landslide data are used to establish a complete understanding of the dynamic interaction between anthropogenic activities and landslide vulnerability. Road construction, construction activities, and deforestation are the human-impacted parameters, and slope, elevation, aspect, plan curvature, profile curvature, precipitation, and drainage systems are the parameters that represent the geographical features of the study area. Data collection and questionnaire formation are based on the selected parameters. Cochran's formula is used to determine the sample size for the perception survey at the landslide location with landslide I and landslide III categories. Simple random method and snowball method were used to conduct the survey. Data collection from residents and the various offices for analysing the cause and impact of landslides. Construction in the past few years occurred on steep slopes without adequate safety measures or drainage planning, increasing surface runoff and triggering slope failures. Field surveys and stakeholder surveys further validated these findings, they mentioned that deforestation, construction activities, poor drainage maintenance, and slope weakening due to road construction as major contributing factors. The frequency ratio method is used for landslide susceptibility analysis. 14 factors are identified in the analysis. Slope, elevation, aspect, plan curvature, profile curvature, Land Use Land Cover, Normalized Difference Vegetation Index, Normalized Difference Built-up Index, stream power index, topographic wetness index, lithology, distance from roads, distance from faults, and rainfall with landslide inventory are the factors used for landslide susceptibility analysis. Landslide susceptibility analysis has been done in two parts to assess the landslide susceptibility change in the past ten years in the city. The analysis shows the impact of urban development on landslide susceptibility. The initial part of the landslide susceptibility analysis is between the years 2015 to 2019, and another is between 2020-2025, with the dynamic parameters as Land Use Land Cover, Normalized Difference Vegetation Index, Normalized Difference Built-up Index, and Landslides inventory. Urban development in the last five years has increased rapidly, and the consequence of this has also been seen. Landslides in the years 2020-2025 have increased, and the 2023 landslides are the best example of this. Proposed projects increase the risk of landslides in the city. After analysing the susceptibility change of the past ten years, the prediction of landslide susceptibility analyses is conducted for upcoming projects in the city. Additional factors used for predictive susceptibility are the distance to the proposed road, distance from new local bus stands, distance from multi-level parking, distance from real estate projects, distance from ropeway stations, distance from 4-lane road construction, and distance from tunnels. It is analysed that the construction of the new projects increases the susceptibility of the city. The elimination of some projects from the existing proposals by the government is proposed to minimize the risk of landslides in the city. No construction zones are proposed to restrict the growing construction. These zones are based on the high landslide susceptibility area identified. Keywords: Landslides, Susceptibility, Urban Development, Slope