Influence of rainfall event characteristics and antecedent conditions on subsurface stormflow response of two forested hillslopes

Abstract

Abstract. Subsurface stormflow (SSF) is a critical runoff-producing mechanism in many upland and mountainous environments, yet the complex relationships between antecedent conditions, rainfall characteristics and SSF response are still not fully understood. Worldwide, the small number of SSF collection systems (trenches), as well as the generally small number of investigated SSF events limit our ability to generalize the findings and explore the influence of a broader range of storm sizes, intensities, antecedent wetness conditions and different hydrogeologic settings. In this study we present a comprehensive analysis of rainfall and SSF event characteristics as well as antecedent conditions, based on data collected at two forested hillslope sites, where SSF was monitored in research trenches over a 2-year period. Our results show that SSF volume is primarily controlled by total rainfall (Ptot) and antecedent wetness, with volumes being up to three orders of magnitude larger under wet initial conditions. At one trench, the volume increased gradually with Ptot, whereas at the other trench SSF volume displayed a threshold-like behaviour, likely linked to the irregular topography of the underlying bedrock. The precipitation threshold varied between ca. 15 and 20 mm for wet and dry antecedent conditions, respectively. Peak SSF flow rates of smaller events were influenced by Ptot and antecedent conditions, but for larger events (Ptot > ca. 20 mm), rainfall intensity was one of the dominant controls along with the rainfall amount preceding peak rainfall intensity. The steepness of the rising limb of the SSF hydrograph was correlated with Ptot and rainfall intensity. The antecedent soil moisture index (ASI) together with Ptot showed a high correlation with most SSF characteristics. The seasonal analysis revealed that, statistically, the largest SSF volumes occurred in winter, while the highest peak flows and rising rates were observed in spring and summer.

Affiliated Institutions

• University of Freiburg DE
• Austrian Research Centre for Forests AT
• GFZ Helmholtz Centre for Geosciences DE
• University of Bayreuth DE
• Universität Innsbruck AT

Related Publications