Rainfall concentration under olive trees

To determine the existence of rainfall concentration beneath olive trees, throughfall and stemflow was measured in three olive trees during 12 rainfall events, using 36 rain gauges per tree and a stemflow collection system. Data from different rainfall events were aggregated to assess the spatial correlation in throughfall. Only one out of the three trees showed a clear spatial dependency structure. Rainfall concentration under the tree canopy, as a consequence of rainfall redistribution of throughfall, was relatively unimportant with few and sparse locations showing a percentage of throughfall with respect to rainfall in open area >100% and none above 125%. Throughfall showed a consistent storm to storm pattern in spatial distribution among high rainfall events, and non-consistent patterns among low rainfall events. Stemflow was found to be the most important mechanism of canopy induced flux concentration, in events where rainfall depth was large enough to saturate the olive canopy. Stemflow was estimated to infiltrate in a radial area up to 0.5 m from the tree trunk, depending on tree characteristics and rainfall intensity. The area surrounding the tree trunk appears to be the most relevant area for potential research dealing with the influence of concentrated canopy induced water fluxes on the transport of chemicals to deeper layers within the soil.