MONTHLY MONITORING OF SURFACE WATER RESERVOIRS IN THE STATE OF PIAUÍ (BRAZIL) USING SATELLITE IMAGES AND CLOUD COMPUTING (2015 – 2021)

Abstract

The objective of this work was to monitor the variation of the surface water extension of eight reservoirs in the state of Piauí, Brazil, and to evaluate the influence of precipitation on them. Monthly monitoring was carried out between 2015 and 2021 based on the Modified Normalized Difference Water Index (MNDWI), generated with images from the Sentinel-2 satellite, MultiSpectral Instrument (MSI) sensor, using Google Earth Engine. The association between surface water extension and precipitation was evaluated based on the correlation matrix. The results indicate that Lagoa do Portinho and the dam of Bocaina are in the process of recovering the stored volume, reflecting an increase in the extension of the water surface, opposite to what was observed in Lagoa de Parnaguá. Considering all reservoirs, a weak negative correlation was observed between the analyzed parameters. However, data from Lagoa do Portinho and Mesas de Pedra, Jenipapo and Algodões II dams showed a moderate positive correlation between surface water extension and rainfall recorded in previous months. The data suggest that other factors may be interfering with water stocks, such as changes in land cover and use, clandestine derivations, as well as groundwater contributions.