| Abstract | Flash flood analysis in mountain areas presents specific challenges due to a lack of spatially well distributed rain and stream gauges with long enough records. In this case, dendrogeomorphology allows improvement of the understanding of the spatial and temporal occurrence of past events. Flash floods may influence trees in different ways and trees react to these disturbances with specific growth and anatomical changes. In this study, we sampled 90 cross sections and 265 increment cores of trees heavily affected by past flash floods to date past events in two ungauged basins in the Spanish Central System. The first study site is located along the Pelayo, a torrent in natural conditions. Based on the external disturbances of trees and their geomorphic position, 114 Pinus pinaster (Ait.) (265 increment corers) were sampled using an increment borer. Based on the number of trees showing disturbances, the quantification of disturbance intensity and the spatial distribution of these trees in the field, seven flash flood events were dated for the last 50 years: 2005, 2000, 1996, 1976, 1973, 1966 and 1963. The second study site is a reach of 2 km length along the Arenal River, where the stream is channelized. Here stumps from previously felled trees could be analyzed directly in the field: 100 Alnus glutinosa (L.) Gaertn. and Fraxinus angustifolia (Vahl.) cross sections were directly investigated in the field and 22 cross sections sampled and analyzed in the laboratory. Based on the injuries dated in the field and in the laboratory, and based on the location of the trees, eight events were dated for the last 30 years: 2005, 2003, 2000, 1998, 1997, 1995, 1993 and 1978. The strength of dendrogeomorphology in flood analysis has been demonstrated, especially in areas where the lack of historical documents, rainfall and flow data limits the use of traditional methods. |