Remote analysis of the chlorophyll-a concentration using Sentinel-2 MSI images in a semiarid environment in Northeastern Brazil Aranha, T. R. B. T. /Martinez, Jean-Michel Souza, E. P. Barros, M. U. G. Martins, E. S. P. R. remote sensing water quality chlorophyll-a reservoirs semiarid In this paper, the authors use remote-sensing images to monitor the water quality of reservoirs located in the semiarid region of Northeast Brazil. Sentinel-2 MSI TOA Level 1C reflectance images were used to remotely estimate the concentration of chlorophyll-a (chl-a), the main indicator of the trophic state of aquatic environments, in five reservoirs in the state of Ceara, Brazil. A three-spectral band retrieval model was calibrated using 171 water samples, collected from November 2015 through July 2018 in 5 reservoirs. For validation, 71 additional samples, collected from August 2018 through December 2019, were used to ensure a robust accuracy assessment. The TOA Level 1C products performed very well, achieving a relative RMSE of 28% and R-2 = 0.80. Data on wind direction and speed, solar radiation and reservoir volume were used to generate a conceptual model to analyze the behavior of chl-a in the surface waters of the Castanhao reservoir. During 2019, the reservoir water quality showed strong variation, with concentration fluctuating from 30 to 95 mu g/L We showed that the end of the dry season is marked by strong eutrophic conditions corresponding to very low water inflows into the reservoir. During the rainy season there is a large decrease in the chl-a concentration following the increase of the lake water storage. During the following dry season, satellite data show a progressive improvement of the trophic state controlled by wind intensity that promotes a better mixing of the reservoir waters and inhibiting the development of most phytoplankton. 2022 text https://www.documentation.ird.fr/hor/fdi:010084301 fdi:010084301 Aranha T. R. B. T., Martinez Jean-Michel, Souza E. P., Barros M. U. G., Martins E. S. P. R.. Remote analysis of the chlorophyll-a concentration using Sentinel-2 MSI images in a semiarid environment in Northeastern Brazil. 2022, 14 (3), 451 [22 p.] EN BRESIL ZONE SEMIARIDE CEARA ETAT