A country-wide spatial assessment of landslide susceptibility in Romania Dan Bălteanu a, ⁎, Viorel Chendeş b , Mihaela Sima a , Petru Enciu a a Romanian Academy, Institute of Geography, Dimitrie Racovita St., 12, sector 2, Bucharest, 023993, Romania b National Institute of Hydrology and Water Management, Sos. Bucuresti - Ploiesti 97, Bucharest, sector 1, 013686, Romania abstract article info Article history: Received 15 May 2009 Received in revised form 26 February 2010 Accepted 2 March 2010 Available online 11 March 2010 Keywords: Landslide susceptibility Romania Spatial distribution GIS This paper proposes a brief spatial analysis of landslides in Romania, completed by a landslide susceptibility model. Landslides constitute a very common geomorphic hazard in this country, mainly in the hilly regions which occupy around 30% of Romania's territory. The landslide susceptibility assessment at national level was accomplished using a Landslide Susceptibility Index (LSI) computed in GIS, which considers and weights the main factors that control landslide activity: lithology, slope gradient, maximum rainfall in 24 h, land use, seismicity and local relief. Each factor was classified into 7–18 classes which were rated from 1 to 10 by means of expert judgement. A formula was devised to compute the Landslide Susceptibility Index over each 100 m × 100 m pixel and the resulting values were ranked into 5 landslide susceptibility classes. This synthetic method of landslide susceptibility assessment, applied to the whole country, is a useful tool to evaluate the distribution of landslide-prone areas, as well as to validate and to enhance some results obtained in previous studies based on field research and map interpretation. The most landslide-prone areas correspond to the Subcarpathians (an outer fringe of hilly terrain accompanying the Carpathians), as well as to the Moldavian Plateau in the east. The semi-quantitative approach has been validated with satisfactory results in a particular sector using independent cartographic landslide inventories. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Romania is one of the Central European countries more severely affected by natural hazards (floods, landslides and earthquakes), all with strong economic and social impact. Landslides comprise all the failure and movement mechanisms, e.g. slides, lateral spreading, flows and falls (Fig. 1). Mountains, hills and tablelands, which cover two- thirds of the country's area, are particularly susceptible to landsliding, especially the hills and tablelands. Numerous historical documents from the 15th–19th centuries contain information on landslide related damage, but it is only since the early 20th century that scientific inventorying and appropriate mapping exist. One of the first landslide classifications applied in Romania distinguished three types of movement mechanisms on slopes: rolling, falling and sliding (Mihăilescu, 1939). Later on, most authors took into consideration in landslide descriptions the mechanism of movement and the type of material, applying Varnes' (1978) classification (Bălteanu, 1983). Geomorphological maps and maps of active geomorphic processes on the scales of 1:10,000 and 1:200,000, which include information on landslides, were produced by the Institute of Geography of the Romanian Academy during the 1975– 1988 time interval. The age of the deep-seated Transylvanian landslides was evaluated based on pollen records from sediments filling closed depressions developed on landslides. These studies revealed that those landslides date back to the late Pleistocene – early Holocene (Preboreal and Boreal ages, 10–7.1 ka) (Morariu and Gârbacea, 1968). Small-scale country-wide cartographic syntheses suggest different degrees of landslide susceptibility and the variability of spatial frequencies depending on the landslide type (Tufescu, 1964). Similar results have been obtained by means of regional studies on the spatial distribution of landslides (Posea et al., 1974) and mapping areas dominated by different geomorphic processes (Bălteanu and Mateescu, 1975; Bălteanu and Posea, 1983). Recent landslide studies in Romania have been focused on the application of quantitative or qualitative methods to develop susceptibility and hazard assessments in several regions of the country (Surdeanu, 1998; Driga and Ciupitu, 2007; Micu and Bălteanu, 2009). However, a landslide susceptibility assessment of the whole country, considering as many causal factors as reasonably possible, and which could be used in a GIS environment by the institutions involved in risk assessment and management, is still lacking. In the present article, landslide susceptibility according to Glade and Crozier (2005) is defined as the relative spatial probability of new landslide occurrences, thereby excluding such elements as magnitude and temporal probability, which are implicit in the notion of hazard (Guzzetti et al., 1999; Parise, 2001). A guide for the elaboration of “landslide risk maps” (actually susceptibility maps) was proposed by the Ministry of Local Public Geomorphology 124 (2010) 102–112 ⁎ Corresponding author. Tel.: + 40 21 3135990; fax: + 40 21 3111242. E-mail address: danbalteanu@clicknet.ro (D. Bălteanu). 0169-555X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2010.03.005 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph