Hydrological spatial coupling within an abandoned Mediterranean terraced microcatchment

Abstract. Runoff (R) generation in Mediterranean headwater catchments is highly episodic and shaped by the interplay of precipitation (P), seasonal soil moisture (SM) dynamics, and terrain structure. In terraced landscapes, land abandonment has driven a forest transition that increases fuel loads and wildfire occurrence, while legacy features such as stone walls modify storage and flow pathways, affecting hydrological spatial coupling. Wildfires further reduce vegetation cover, induce soil water repellence, and lower infiltration capacity, enhancing R generation and reorganising connectivity during a post-fire window of disturbance, but their interaction with terrace structure at event scale is poorly understood. This study investigates how P, seasonal evolving SM, and terrain structure control R in a 4.7 ha terraced microcatchment in Mallorca, Spain, affected by a high-severity wildfire in 2013. Hydrological conditions were classified into four periods (wet, drying-down, dry, and wetting-up). P, SM, and discharge (Q) were continuously monitored over four years (2021–2024), with SM measured at representative hillslope and terrace locations. Of 186 P events analyzed, only 17% generated measurable outlet Q, with R highly concentrated in time: November 2021 alone accounted for 73% of total R volume. Maximum SM consistently emerged as the strongest indicator of R occurrence across seasons, while event-scale changes in SM (ΔSM) were particularly informative during transitional periods; antecedent SM showed limited predictive power, especially under partially coupled conditions. Hillslopes responded rapidly to P but with weak coupling between local SM and outlet Q, whereas farm terraces exhibited storage-controlled behaviour in well-connected positions and delayed or suppressed responses in disconnected mid-terrace areas. Overall, R emerges from the interaction between P forcing, dynamically evolving SM, and spatially variable structural connectivity, rather than from static thresholds, highlighting the need for connectivity-aware, event-scale approaches to inform land management in Mediterranean landscapes under global change.