Modelling and analysis of landslide-rainfall relationship in Trabzon province

Knowing the duration, amount and intensity of precipitation triggering landslides is of great importance for landslide prediction and landslide warning systems. Recent researches indicate that landslides occur after passing a certain threshold value of rainfall. Trabzon province which has the highest rainfall in Turkey, is located in a region where landslides mostly occur. Due to that fact; the ability to determine the rainfall threshold for Trabzon province becomes necessary in order to prevent landslides and mitigate landslide hazards. In this study, following the definition of rainfall threshold, a database will be provided for establishing landslide early warning system. Empirical method based on statistical data was used to determine a rainfall threshold for Trabzon slopes which are mainly made of residual soils. Through this study, rainfall thresholds which trigger Trabzon province landslides were determined for different parameters (multiple landslides, slope angle, purpose of land use etc.). To increase the correlation reliability, number of landslides and rainfall data (n=1105) were used to obtain rainfall thresholds for a local region that could be considered as small size region. Then, the calculated rainfall threshold for Trabzon province within the considered soil parameters was verified with numerical models. Due to often landslides occurrence on slopes of lands which are converted from forests to agricultural lands, the effect of tree roots on slope stability were also separately evaluated. The database of landslide early warning system for Trabzon province was comprised from these rainfall thresholds. The reliability of landslide early warning system database was verified over a 2-years trial period (2009-2010) and ensured high consistency. With the installation of a landslide early warning system using rainfall thresholds, life and property losses due to landslides in Trabzon province will be reduced. Thus, social and economic benefit will be realised not only for Trabzon, but also for our entire country.