Linked spatial variability of throughfall amount and intensity during rainfall in a coniferous forest

Routing of rainfall through forest canopies causes spatial variability in throughfall amounts and intensities, but the covariance of these effects has not been investigated. We investigated the relationship between point throughfall amount and intensity reduction in an old-growth seasonal temperate rainforest in southwestern Washington, USA, using tipping bucket rain gauges both under and above the coniferous forest canopy. Mean hydraulic residence time of rainfall in the canopy was 25 min, with event means ranging between 4 and 52 min. Locations of high throughfall accumulation received throughfall at intensities similar to rainfall, and locations of low accumulation experienced more variable intensities. Drip points funneling water to zones of high accumulation are not typical of this coniferous seasonal temperate rainforest. There was a positive relationship between intensity reduction by the canopy and evaporation during rain events that indicates that refilling of storage made available by evaporation is important for buffering throughfall intensities.