RAINFALL TRIGGERED LANDSLIDES IN TRABZON PROVINCE, TURKEY E. Eris Ege University, Izmir H. Aksoy Istanbul Technical University, Istanbul

Disasters in Turkey Disaster Proportion (%) Earthquakes 61 Landslides 15 Floods 14 Rock falls 5 Forest fire 4 Snowslide 1 • 25% of country area is exposed to landslide hazard. • 11% of total population is located in landslide areas. • 15 % of total disaster losses are due to landslides.

Spatial distribution of landslide events in Turkey

Trabzon Province

Trabzon Province Elevation increases from sea level to reach up to 3000 m. Generally, mountains, hills and high plateaus take part in inner lands of the region. Trabzon has mild and humid climate with a heavy uniform rainfall and relatively warm temperatures all year round.

Annual rainfall of 9 rainfall gauges in Trabzon

Landslides & Rainfall Climate type map Landslide density map

Source: Disaster and Emergency Presidency (AFAD) Between the years of 1929-2012

Landslides & Rainfall Uzungol gauge Trabzon gauge Event date 21 November 2009 2 people dead Trabzon gauge Event date 19-20 June 1990 56/65 people dead

Threshold Analysis The thresholds are usually obtained by drawing lower-bound lines to the rainfall conditions resulted in landslides.

Threshold Analysis 2.5 h  D  40 h The most important 27 rainfall-triggered landslides between 1990 and 2009. Local and national administrations, technical and scientific articles, thesis and internet news

Some of rainfall intensity-duration threshold equations Study by Area Equation Caine (1980) Over the world I= 14.82 D-0.39 Cancelli and Nova (1985) Northern Italy I= 44.67 D0.78 Wieczorek (1987) California I= 1.7+9 D-1 Crosta and Frattini (2001) I= 0.48+7.2 D-1 Aleotti (2004) Italy I= 19 D-050 Guzetti et al. (2007) Mid-latitude climate for D<300h I= 18.6 D-0.81 Mid-latitude climate for D>300h I= 0.82 D-0.19 Dahal and Hasegawa (2008) Himalaya, Nepal I= 73.90 D-0.79 Baltacı (2010) Trabzon I= 8.641 D-0.4591 Akçalı and Arman (2013) Trabzon for D<6h I= 57.73 D-2.33 Trabzon for D>6h I= 2.75 D-0.63 This study (2014) I= 20 D-0.80

Some of rainfall intensity-duration threshold eq. According to Guzzetti et al. (2007) power is between -0.70 and -0.81 for mid-latitude climates power is between -0.48 and -0.64 for the mountains and cold climates

Conclusions The proposed equation seems to be a reasonable approximation when it is compared to previous equations developed from data of landslides in Trabzon. For the risk mitigation studies, landslide early warning systems can be implemented by using rainfall-landslide thresholds as proposed in this study. The proposed empirical relation takes rainfall into account only; it does not account for other factors causing landslide such as slope, land use, vegetation, etc. There are only a few intensity-duration threshold studies on landslides at local scale in Turkey. At present, such a general threshold relation is not available for the whole country. This can be considered an important gap in terms of both research and practice.

Thank you… Ebru Eris ebru.eris@ege.edu.tr Hafzullah Aksoy haksoy@itu.edu.tr