Examining the Role of Meteorological Conditions and Throughfall Drop Sizes

Abstract:

The partitioning of incident precipitation by a forest canopy into throughfall and stemflow varies as a function of meteorological conditions, tree species, leaf morphology and surface roughness, among other factors. Nanko et al (2015) examined the throughfall drop size signature of precipitation events relative to changes in leaf canopy state of deciduous forests. However, little work has been done to quantify the influence of meteorological variables (air temperature, wind speed, wind direction, rainfall intensity and duration) on drop size among discrete rain events. To quantify individual throughfall drops, a laser disdrometer gauge was deployed below an observed drip point under a Liriodendron tulipifera L. (yellow poplar) tree, in northeastern Maryland, USA. Based on events > 5mm rainfall, more than 850,000 individual throughfall droplets have been analyzed from precipitation occurring between September 2013 and October 2014. Building on previous work, which has examined the substantial influence of canopy state over the drop size spectra, this work focuses on the impact of inter-event variability in meteorological conditions and their differential effects on maximum drop size and throughfall depth received. Preliminary statistical analyses indicate that wind speed, wind direction, and air temperature are the primary factors governing throughfall drop size distributions. Since these factors do not consistently influence throughfall drop size distributions in the same manner, further in-depth analyses will attempt to uncover the dynamic interplay among these mutually interacting factors. Results from this study are expected to increase our understanding of the rhythms and mechanisms of throughfall hotspot appearance and disappearance.