Characterization of water status and vegetation cover change in a watershed in Northeastern Brazil

Abstract

The existing water scarcity in the Brazilian semiarid region, associated with anthropic activities, imply in the degradation of the watersheds present in the Caatinga. Therefore, the objective of this study was to characterize water and vegetation cover changes in the Ipanema River Watershed (IRW). IRW is inserted in municipalities that make up the dairy basins of the states of Alagoas and Pernambuco, one of the main economic activities in the Northeast of Brazil (NEB). Land use and land cover (LULC) maps, Modified Normalized Difference Water Index (MNDWI) and rainfall product via TerraClimate were used in the study. The MNDWI was based on the annual mean between 2010 and 2020 for the dry and rainy periods. For rainfall patterns and variability, pixel values were extracted and submitted to the Inverse Distance Weighted (IDW) interpolation method. We highlight the inverse relationship between the categories Forestry, Agriculture and Cattle Raising, with a decrease in the area of Caatinga due to agriculture and cattle raising. In the dry period via MNDWI there was higher water availability in 2010, 2017, 2018, 2019 and 2020, the exceptions were the years 2013–2016. In the rainy season, clouds interfered in the MNDWI analyses, with lower water availability in 2013, the exceptions were 2017 and 2018. Comparatively, the images from 2010 to 2020 via MNDWI, showed a water reduction in the IRW, mainly in the southern portion. For the dry period, the years 2011, 2012, 2016 and 2019 showed less than 138 mm of rainfall, especially in 2016 (<64 mm). In the rainy season, the years 2012, 2013, 2016, 2018 and 2019 also showed less than 482 mm of rainfall, with 2012 and 2016 standing out (<101 mm), mainly, the months with the highest rainfall record at IRW. The results obtained in this study show that droughts in the NEB continue to the present day, followed by an increase in water deficit. Anthropic action implies environmental degradation in one of the most threatened ecosystems (Caatinga), affecting mainly the water resource, an important factor in the survival of the local population and in the territorial dynamics.