The History of the Dunes
Rainy season: water builds the landscape
The Lencois receive abundant rainfall, reaching around 2,000 mm per year. More than 90% of that rain — concentrated between January and July — is quickly absorbed by the sand. The groundwater table rises above the surface and temporary lagoons fill the interdune basins. During this wet period the dunes barely move, because moisture binds the sand and winds are weaker. Lagoons commonly reach about 1 meter in depth.
Dry season: wind reshapes the dunes
From July to December, regional winds strengthen and lagoon water levels fall. As moisture decreases, sand bodies become more mobile and dunes can shift location in a few months. This is when migration rates peak and interdune routes change.
A year like a moving board
In the first half of the year (wetter months), there is less wind and a higher water table, so dunes tend to remain where they are. In the second half (drier months in Maranhao), winds intensify and dunes migrate — as if pieces on a board were changing positions.
Water vs. sand using SAR backscatter; seasonal changes in texture; dune migration using Amplitude Offset Tracking.
These seasonal shifts affect access routes, fishing, tourism, and water availability for communities like Santo Amaro and Atins.