Influences of vegetationand rainfall patterns on scaling in Hortonian rainfall-runoff processes

Abstract:

The Hortonian rainfall-runoff process is a critical player for ecosystem in semi-arid regions. It has long been recognized that this process is scale dependent, which may have fundamental impact on water resources distribution and ecosystem sustainability in these regions. Recent studies have disclosed complex feedbacks between rainfall, vegetation patches, microtopography and layered soil characteristics in semi-arid ecosystems. The interactions, however, may also affect the scaling of the process. To quantitatively study the impact of vegetation and rainfall properties on the scaling of the rainfall-runoff process, a modeling approach coupling a two-dimensional surface runoff model and a two-layer conceptual infiltration model was employed. Having been validated in a semi-arid field plot in the Lehavim LTER in Southern Israel, the model was applied to a series of plots of varying scales with statistically identical distributions of land surface properties to examine the vegetation and rainfall impact. The approach provides a basis of comparison for the hydrological responses at various scales. Influences of regular and random vegetation patterns were compared with the Monte Carlo simulation approach. Also examined are the influences of rainfall intensity and rainfall temporal variability. Results show that these impacting factors affect the spatial distribution of infiltration, local as well as global runoff generation at all scales. All these factors affect the scale dependence of Hortonian runoff, while the trends of the scaling laws are expected to maintain.