La Marjal de Gandia is a protected Mediterranean wetland characterized by high hydrological variability and increasing environmental pressure. This study quantifies the temporal dynamics of open water within the official wetland boundary over 2015–2025 using Sentinel-2 multispectral imagery processed on the Google Earth Engine platform. Water surfaces were automatically extracted through spectral index-based classification (e.g., NDWI/MNDWI), enabling the generation of an annual flooded-area time series. Historical orthophotographs from 2015 were used to derive reference land-use information and support training data selection, while land-use conditions for 2025 will be validated through field observations during 2026.

The study also analyses how hydrological fluctuations relate to seasonal rainfall, agricultural water management and vegetation cycles. The incorporation of multi-temporal imagery enables the detection of short-term flooding and long-term trends, offering a consistent overview of the wetland’s functional dynamics. By integrating remote sensing, land-use data and in situ verification, the methodology provides a robust framework for assessing wetland condition.

Previous studies indicate that open water in Mediterranean wetlands can vary by 20–50% across seasons and years. Preliminary inspection of Sentinel-2 data suggests that flooded surfaces in La Marjal may range from below 10 ha during dry months to more than 40 ha after intense precipitation events, consistent with patterns observed in similar coastal wetlands.

The expected results will support hydrological interpretation and conservation planning and demonstrate the value of Sentinel-2 monitoring for Mediterranean wetlands.