On the Distribution of Interflow Downslope Travel Distances and Slope Characteristics—An Expanded Meta‐ Analysis of Hillslope Studies

Abstract Interflow processes are often studied through measurements and models at individual hillslopes or small catchments, highlighting the need for broader data analysis. To address this gap, we compiled data from 35 studies encompassing 69 hillslopes from which we plotted and analyzed distributions of interflow downslope travel distances (DTDs) for matrix flow, topsoil conductivities, impeding layer conductivities, topsoil depths, and slope gradients across the types of hillslopes that interest interflow researchers. Interflow studies are conducted on hillslopes that are steep (median = 0.32) relative to the median slope around the world (0.09). Even within slope‐biased data, 50% of DTDs were less than 7.8 m, and 65% were less than 30 m. At six slopes, DTDs exceeded 100 m. Ratios of upper soil conductivities to impeding layer conductivities were highly variable and right‐skewed, ranging from 2 to 4,700, with median and mean of 25.4 and 242, respectively. Slopes were also right‐skewed, ranging from 0.02 to 1.1, with median and mean of 0.32 and 0.39. Thicknesses of the upper soils promoting interflow ranged from 0.15 to 1.8 m, with median and average of 0.70 and 0.86 m. The extended data set confirms that while perched interflow is an important process in steep hillslopes, its role in connecting slopes to valleys is often spatially limited, challenging the traditional binary view of interflow as a widespread stormflow generation mechanism. Future research should examine interflow process across broader landscapes, integrate larger data sets, and improve hydrologic models to better capture the spatial variability and connectivity of perched interflow.