Spatial Heterogeneity of Soil Water after Large Rainfall Events in a Dry Forest: Interacting Canopy, Surface and Soil Effects

Abstract:

Ecohydrology of dry forest depends on the proportion of rainfall that enters the soil and it is spatial distribution at the patch scale. While the central role of patch scale redistribution has been widely documented, we know less about its response to rainfall intensity and its interplay with site properties (canopy, surface, soil). Here we explore water capture (infiltrated water depth, 24 hours after a rainfall event) and its determinants at the patch scale in a forest stand of the Dry Chaco (33.47 S, 66.44 W, Argentina). Water capture from 4 large rainfall events (>30 mm) was measured along 3 transects (36 m) in 18 regularly spaced (2 m) microsites, complemented by 2 years of hourly TDR moisture measurements in 3 microsites. Twelve canopy, surface and soil variables were characterized at each microsite. As the intensity of rainfall increased across events (9 to 34 mm/h) the heterogeneity of water capture became larger (coefficient of variation from 29 to 53%). Despite the intense internal redistribution of rainfall, net runoff was virtually nil (<3%) for all events, showing high capture at the stand level. Microsite variables influencing water capture changed with rainfall intensity. Canopy and soil litter cover reduced microsite water capture for the lowest intensity event (r=-0.44 and -0.37, respectively), but favor it for the highest intensity one (r=0.44 and 0.39, respectively). On intermediate intensity events water capture was predominantly explained by microtopography (greater capture in low microsites, p<0.05). Frequent TDR measurements supported these results. Water redistribution responds to rainfall intensity, creating different water capture patterns (contrasting effects of microsite conditions) for each rainfall event, an issue that may strongly influence key ecohydrological process such as E/T partition at the stand level. This study expands our perspective on dry forest water capture by quantifying its response to rainfall intensity.