Monitoring water surface elevation dynamics in the Brazilian Pantanal wetland using radar altimetry

With its complex hydrological dynamics and high diversity of habitats, the Pantanal, a large South American wetland, is increasingly threatened by anthropogenic activities and climate change. In such vulnerable ecosystems, radar altimetry is a key source of Water Surface Elevation (WSE) measurements and, thus, fundamental for monitoring these often remote and poorly gauged environments. This study assesses the potential of the Sentinel-3 and Sentinel-6 missions to monitor hydrological dynamics in the Brazilian Pantanal (May 2016 to March 2024). We first evaluated the agreement between radar altimetry and in situ WSE and then demonstrated the contribution of these data to characterizing three distinct hydrological features across this large tropical wetland. Our results showed strong agreement between altimetry and in situ water levels, with correlation coefficients (R) greater than 0.85 and Root Mean Square Errors (RMSE) below 0.4 m in most cases. Using this extensive radar altimetry network, we demonstrated backwater flooding on the Miranda River, which experiences two annual flood cycles driven by local precipitation and the Paraguay River’s flood pulse. This dynamic was disrupted by recent megadroughts. We also detected significant WSE declines in the shallow lakes of the Nhecolândia region, directly linked to the megadroughts, and revealed along-channel variations in seasonal water level patterns across the ungauged Taquari megafan, a distributive fluvial system likely subject to the combined pressures of upland agriculture and climatic extremes. These findings underscore the high potential of radar altimetry for monitoring and understanding complex hydrologic dynamics in vulnerable ecosystems like the Pantanal. • Radar altimetry water surface elevation (RA-WSE) is assessed in the Pantanal wetland. • Sentinel-3 and -6 WSE estimates are higly correlated with in situ records (R > 0.85). • RA-WSE reveals backwater flooding dynamics within the Paraguay River system. • RA-WSE tracks persistent lake-level decline in Nhecolândia region after megadroughts. • RA-WSE enables monitoring of hydrological dynamics in the ungauged Taquari megafan.