Seasonal and Hydroclimatic Dynamics in Wetlands Using Spectral Indices and Water Balance in Different Geomorphological Units

Wetlands perform essential ecological functions and are sensitive to hydroclimatic variations. This study analyzed the hydrological dynamics of wetlands located in two geomorphological units in the far south of Brazil. We integrated time series (2016–2024) of precipitation (CHIRPS), evapotranspiration (MODIS MOD16A2), and Sentinel-2 images processed in Google Earth Engine, and applied the NDWI, NDMI, and MNDWI indices to map water surfaces. The results indicate that MNDWI was more effective in identifying flooded areas, especially in environments containing vegetation and sediments. The water balance analysis (P-ET) revealed distinct seasonal patterns: (1) greater stability and extensive flooded areas; and (2) irregular pulses and prolonged periods of water surface retreat. Evapotranspiration displayed seasonality, peaking in summer, while precipitation had an irregular pattern with greater amplitude during extreme events. Wetland responses to climatic variability were directly tied to local geomorphology and water storage capacity. These findings underscore the importance of using time-series and remote sensing in wetland monitoring, especially in the face of climate change. The proposed methodology is replicable and supports wetland conservation and mapping through the interplay between spectral indices and water balance.