Kalka Shimla Railways – A UNESCO World Heritage Site Exposed to Landslides

The Kalka Shimla Railway was built in the mid-19^th century during British rule in India to connect Shimla, then the British summer capital and the headquarters of the British army, with the Indian rail network. Considered the “Crown Jewel” of the Indian National Railways during British times, the rail network features in the Guinness Book of World Records for its steepest rise in altitude, from 656 m at Kalka to 2,076 m at Shimla in a span of 96.57 km. It was granted UNESCO World Heritage Status in 2008 for its profound impact on the social and economic development of the high mountain areas. Despite conservation management plans and regular permanent maintenance, the track faces the vagaries of nature. Slips and landslides, in particular, cause frequent disruptions in its operations. The present study focuses on susceptibility mapping for the Kalka Shimla Railway, often dubbed the “Toy Train”, to determine the degree of its exposure to landslides. Data from 1,484 past landslide locations is used to train a Random Forest classifier with Bayesian hyperparameter optimization to ensure accurate classifications. The trained model is validated using 5-fold cross-validation with an accuracy of 90.6% and an area under the receiver operating characteristic curve (AUROC) value of 0.97. The accuracy and AUROC values during the testing stage for the model are 91.7% and 0.97, respectively. The final susceptibility map is validated using the landslide density method after dividing the posterior probabilities into five classes based on Jenks optimization. The landslide densities of the five susceptibility zones, namely “Very High”, “High”, “Medium”, “Low” and “Very Low” are 17.180, 0.196, 0.036, 0.008, and 0.001 respectively, which reflect the quality of susceptibility zonation mapping because 96.55% of all the landslides lie within only 5.62% of the study area with “Very High” susceptibility. The results of the study show that 36.9% of the total length of the railway is exposed to either “High” or “Very High” landslide susceptibility. The degree of exposure is particularly severe in the Solan district where landslides have interrupted the normal operations of the railway as recently as the last monsoon spell in the region. The results of this study may help policymakers and concerned authorities implement decisive protection measures for the preservation of this heritage site and its outstanding legacy.