Temporal persistence of spatial patterns in throughfall

Spatial and temporal variability of throughfall beneath forests are potentially important controls on soil processes, watershed hydrology, and biogeochemistry. We used a set of 94 rain gauges to measure variability of throughfall beneath three forest stands in the Pacific Northwest, USA. The length scale over which throughfall amounts were correlated (spatial correlation lengths) was between one-half- and one crown diameter in mid-age and old stands of conifers. In a deciduous stand, the spatial correlation length was about one crown diameter when in leaf condition and throughfall was not correlated spatially in leaf-off condition. Spatial patterns of storm-total throughfall were temporally stable in two ways: semivariograms, which provide a measure of the continuity of a spatial phenomenon, were similar among storms, and throughfall amounts of an individual gauge could be predicted relative to the plot average. Time stability plots of throughfall amounts, normalized with respect to mean and variance, were useful for comparing temporal persistence of spatial throughfall variability among stands. Together, semivariograms and time stability plots appear to be suitable descriptors of throughfall variability for modeling water flux at the soil surface.