Spatio-temporal dynamics of reservoir storage in the Algarve region (Southern Portugal): implications for regional water security

ABSTRACT The Algarve region in southern Portugal relies heavily on reservoirs to support domestic water supply, irrigation, tourism, and other economic activities. This study examined the spatio-temporal dynamics of storage in six major reservoirs: Bravura, Arade, Funcho, Odelouca, Odeleite, and Beliche, using monthly and annual storage data from 2012 to 2025. Time-series analysis, inter-reservoir comparisons, and assessment of combined regional storage were conducted to evaluate temporal variability and drought-related changes in water availability. The results revealed considerable interannual variability in reservoir storage. Combined storage reached its highest levels in 2013 (332.6 Mm3), 2014 (325.0 Mm3), and 2025 (332.9 Mm3), while the lowest levels occurred during the severe drought years of 2023 (153.6 Mm3) and 2024 (155.2 Mm3). Reservoirs in the Guadiana basin, particularly Odeleite, showed greater resilience to prolonged drought than those in the western Algarve. Bravura Reservoir exhibited the highest variability, with storage ranging from 9.0 to 99.2% of capacity. Seasonal analysis indicated that storage generally peaked between March and May, reflecting delayed catchment responses to winter rainfall. The findings highlight the vulnerability of Algarve water resources to droughts and emphasize the need for adaptive water management strategies: water reuse, desalination, rainwater harvesting, and groundwater use, to strengthen long-term water security.