LANDSLIDES RAINFALL THRESHOLDS APPROACHES FOR THE WESTERN GHATS INDIA AND THE NORTH CAUCASUS (Russia)

Abstract

Knowing the duration, intensity and amount of precipitation triggering landslides is of great importance for landslide risk management. Global, regional and local studies carried out by the researchers revealed that the rainfall-induced landslides occur after rainfall exceeding a certain threshold value. The rainfall threshold is the minimum intensity or duration of rainfall required to initiate the landslide. The Rainfall threshold can be estimated from the daily rainfall data which is collected from the rainguage. The methodology used by Jaiswal and Van Westen and ITC Netherland are used for the present study. Daily data from particular rainguage station closer to the landslide location were considered. The 5Days Antecedent (5-AD) rainfall for each year from daily rainfall of landslide events calculated (for 5 days AD, add the previous 5 days of daily rainfall). Then the daily rainfall and the corresponding 5AD rainfall for the all the landslide event in the same period will be plotted. The relation could be presented as a straight line with negative slope of the type RT = p*R5AD + c, where p is the slope and c is the intercept. The present study is focused on the assessment of precipitation thresholds for landslides on different slopes prone to the landslides in Russia and India, which are characterized by very different geological, geomorphological and meteorological conditions. In this article, the main attention is paid to precipitation threshold criteria as the main driver of landslides in India compared to the North Caucasus, in order to find out the contribution of various factors to the processes of landslides for the development of an early warning system. In order to form the landslide inventory map of the territory of the North Caucasus, we used the data of the Information Bulletins on the state of the subsoil of the North Caucasian Federal District for 2019-2020. For all events, there is information about the genetic types of hazardous exogenous processes, activation factors, consequences and damage. Area of Dagestan was selected. Calculations were made for landslides and rockfalls. One can see that slopes of both lines are nearly same p=-0.11-0.12, while landslides need twice a precipitation more than rockfalls. Comparison with rain thresholds for India had shown that for the territory of Russia requires by an order of less total precipitation and precipitation per day. Perhaps, here it is necessary to take into account the contribution of other factors as well. This work is the first stage, and research will be continued. Subsequently, the influence of other factors on the formation of landslides and rockfalls will also be studied (the influence of earthquakes, man-made impacts, etc.) according to the data of various geophysical methods.