Monitoring vegetation and water changes with Sentinel-2 data in long-term trends: Case of study Salar de Atacama (Chile).

The Salar de Atacama is a high-altitude salt flat desert ecosystem. This unique environment is rich in lithium. However, the extraction of this resource poses potential risks to the delicate ecological balance of the region. To assess the long-term impact of mining and climate change on this fragile ecosystem, this study aims to quantify changes in vegetation cover and water bodies within the Salar de Atacama.

Using Sentinel-2 satellite imagery (Level 2A) from July 2015 to June 2024, the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) were calculated using the Google Earth Engine. These indices were classified in Python using thresholds of 0.2 and 0.3, respectively, for the assessment of temporal variability.

To validate the results, the data were compared with the water level and meteorological and vegetation monitoring data from the “Sociedad Química y Minera de Chile” mining company.

Vegetation growth appears to be more strongly correlated with temperature than precipitation, with a two-month lag. An indirect relationship was observed between vegetation patch area and surface water levels.

The natural vegetation patch on the east side of the salt flat exhibits distinct behavior compared to the cultivated areas near San Pedro de Atacama. The natural vegetation patch reaches a maximum NDVI of 0.3, while crops exhibit a wider range of NDVI values, from 0.2 to 0.8. Additionally, the natural vegetation experiences a five-month dormant period (June to November), whereas crops have a shorter two-month dormant period (June to August). Analysis of water level data in the east border of the salt flat revealed no correlation with the near vegetation.

Due to the relatively small size of the lagoons (maximum of 1 km²), monitoring salinity dynamics using satellite imagery alone is challenging. Future studies could incorporate radar imagery to enhance the analysis of surface soil moisture and ground deformation.