Rainfall interception by a Pinus sylvestris forest patch overgrown in a Mediterranean mountainous abandoned area .1. Monitoring design and results down to the event scale

Monitoring (in 5 min steps) of precipitation, throughfall, stemflow and bulk canopy wetness, and also weather conditions and soil moisture, was carried out from July 1993 to December 1995, in a Pinus sylvestris forest patch located in a Mediterranean mountainous former agricultural basin subject to spontaneous change from pasture to forest. Throughfall collectors were designed to obtain hydrologically representative data and they consist of nine troughs with a total catchment area of 9 m(2). The bulk interception rate measured after 30 months of monitoring was about 24%. Relative interception was irregular and decreased with the magnitude of the event; it was at least 15% for events of more than 20 mm. Multivariate analysis of the events demonstrates that their characteristics can be simplified in two main factors which respectively represent the duration of the event and its magnitude. The magnitude of the event biases the characterization because of the non-linearity of the rainfall-interception relationship. Long events do not produce higher interception rates than shorter ones because of the occurrence of low vapour pressure deficits during the former. In atmospheric dry conditions the rainfall intensity provides the main control on interception rates. (C) 1997 Elsevier Science B.V.