Estimativa da área irrigada por pivô central e ocorrência de erosão hídrica na região das Missões

Abstract

Water erosion is identified as the primary cause of soil degradation. Although it is a natural physical process, anthropogenic activities and improper soil management can lead to accelerated erosion, where the rate of soil loss exceeds the rate of soil formation, resulting in economic and environmental impacts. This study aimed to estimate the area irrigated by central pivot systems, identify the occurrence of water erosion, and assess surface runoff management practices in the Missions Region of Rio Grande do Sul State, Brazil. The mapping of central pivots was conducted through visual identification using a mosaic of images from the Landsat 8 OLI/TIRS satellite, accessed via the Google Earth Pro geospatial analysis platform. A digital municipal grid in shapefile format, provided by the Brazilian Institute of Geography and Statistics (IBGE, 2022), was used for territorial delimitation and determining the location of each central pivot. The main hydrographic basins of the region were also identified. Subsequently, central pivots were marked, and the area in hectares was calculated using the tools available on the utilized platform. Additionally, the study analyzed water sources for irrigation, the presence of rills, and the methods of surface runoff control adopted. The collected data were organized by municipality and hydrographic basin and then subjected to descriptive statistical analysis. The Missions Region of Rio Grande do Sul encompasses an irrigated area of 66,363.08 hectares under central pivot systems, with 1,301 pivots identified by October 2024, distributed across 22 municipalities. The municipalities of Cerro Largo, Guarani das Missões, São Paulo das Missões, Porto Xavier, and Ubiretama do not have irrigation through central pivots. Rill formation due to water erosion was observed in 91.77% of the irrigated area, corresponding to 60,903.36 hectares across 1,159 pivots. In 65.56% of the irrigated area affected by erosion, no additional surface runoff control practices were observed, which may exacerbate water erosion problems. In 31.58% of the irrigated area, small retention basins or "barraginhas" were used as surface runoff control methods. In municipalities adopting this practice, 100% of central pivots showed the presence of rills, indicating that these practices have proven ineffective and insufficient for controlling water erosion.