Horizon 1 1 17 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES Water 451 [22 p.] remote sensing water quality chlorophyll-a reservoirs semiarid BRESIL ZONE SEMIARIDE CEARA ETAT 2022 fdi:010084301 ENG Water ISI:000755253400001 3 10.3390/w14030451 https://www.documentation.ird.fr/hor/fdi:010084301 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2022-04/010084301.pdf 14 Horizon (IRD) 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. 062 ; 126 ; 036 UR234 Brésil