Structural and functional control of surface-patch to hillslope-scale runoff and sediment connectivity in Mediterranean-dry reclaimed slope systems

Abstract

Abstract. Runoff and soil erosion in Mediterranean landscapes are affected by multiple factors that interact at a variety of spatial scales with variable degrees of connection. In these systems, connectivity has emerged as a useful concept for exploring the movement of runoff and sediments between landscape locations and across spatial scales. In this study, we examine the structural and functional controls of surface-patch to hillslope-scale runoff and sediment connectivity in three Mediterranean-dry reclaimed mining slope systems that have different long-term development levels of vegetation and rill networks. Structural connectivity, or the extent to which surface patches that facilitate the production of runoff/sediments are physically linked to one another, was assessed using a flowpath analysis of coupled vegetation distribution and surface topography. Functional connectivity, determined as the spatial continuity of surface fluxes across scales, was further explored using the ratio of surface-patch to hillslope-scale observations of runoff and sediment yield for 21 monitored hydrologically active rainfall events. Event-based (functional) runoff connectivity was found to be dynamically controlled by antecedent precipitation conditions and rainfall intensity and, at the same time, was strongly modulated by the structural connectivity of the slopes. In the absence of rill networks, both runoff and sediments for all events were largely redistributed within the analysed systems, resulting in low functional connectivity. Sediment connectivity increased with rainfall intensity, particularly in the presence of rill networks where active incision under high intensity storm conditions led to large non-linear increases in sediment yield from the surface-patch to the hillslope scales. Overall, our results demonstrate the usefulness of applying structural and functional connectivity metrics for practical applications, and for assessing the complex links and controlling factors that regulate the transference of both runoff and sediment yield across different landscape scales.