Influence of rain pulse characteristics over intrastorm throughfall hot moments

Abstract. Forest canopy alters the amount of rainfall reaching the surface by redistributing it as throughfall. Throughfall is critical to watershed ecological variables (soil moisture, stream water discharge/chemistry, and stormflow pathways) and controlled by canopy structural interactions with meteorological conditions across temporal scales (from seasonal to within-event). This work uses complete linkage cluster analysis to identify intrastorm rain pulses of distinct meteorological conditions (beginning-of-storm and internal-to-storm pulses that are atmospherically dry, moderate, or wet), relates each cluster to intrastorm throughfall responses, then applies multiple correspondence analyses (MCAs) to a range of meteorological thresholds (median intensity, coefficient of variation (CV) of intensity, mean wind-driven droplet inclination angle, and CV of wind speed) for identification of interacting storm conditions corresponding to hot moments in throughfall generation (≥ 80% of rainfall). Equalling/exceeding rain intensity thresholds (median and CV) corresponded with throughfall hot moments across all rain pulse types. Under these intensity conditions, two wind mechanisms produced significant correspondences: (1) high wind-driven droplet inclination angles under steady wind increased surface wetting; and (2) sporadic winds shook entrained droplets from surfaces. Correspondences with these threshold conditions were greatest for pulses of moderate vapour pressure deficit (VPD), but weakest under high VPD. Weaker correspondences between throughfall hot moments and meteorological thresholds for high VPD pulses may be because canopy structures were not included in the MCA. In that vein, strongest meteorological threshold correspondences to throughfall hot moments at our site may be a function of heavy T. usneoides coverage. Future applications of MCA within other forests are, therefore, recommended to characterize how throughfall hot moments may be affected along drainage paths dependent on different structures (leaves, twigs, branches, etc.).