Watershed hydrology and ecological resilience in the gravity-fed terraces of the Alhambra

Abstract

The terraced landscape of the Alhambra retains a highly refined gravity-fed irrigation system that provides a unique setting for examining how watershed-scale hydrological processes interact with ecological functions in historic environments. This study investigates the hydrological dynamics, vegetative responses, and microclimatic effects associated with the Alhambra's multi-level terraces to assess their contribution to ecological resilience under contemporary climatic pressures. Based on continuous field observations from 2018 to 2023, reconstructed hydrological pathways, and microclimate profiling, the analysis identified how terrace gradients drove cascade gravity flow distribution, enhanced soil–moisture persistence, and stabilised vegetation performance under seasonal drought and extreme rainfall. Hydrological model calibration and validation (2018–2023) further confirmed the reliability of simulated runoff and infiltration processes, with model performance meeting accepted hydrological standards. Results showed that vegetated terraces yielded a mean steady-state infiltration rate of 27.4 ± 6.1 mm h⁻¹, 5.6 times higher than compacted pathways (4.9 ± 2.0 mm h⁻¹), and reduced peak runoff by 28–36% (P < 0.05). The synergistic mechanism of cascade gravity water conduction, multi-layer vegetative structuring, and micro-topographic shading formed a bidirectional eco-hydrological feedback loop that generated local cooling and buffered thermal extremes, substantially elevating the adaptive capacity of the terrace ecosystem. These findings demonstrate that historic terraced irrigation systems can operate as low-energy, regenerative watershed infrastructures, linking hydrological restoration with microclimate regulation and ecological stability. The study highlights the continued relevance of traditional Mediterranean water-management practices for contemporary climate adaptation frameworks and underscores the value of cultural landscapes as living laboratories for exploring heritage-integrated watershed ecological resilience.