A construção do canal do sertão alagoano impactou a agricultura do semiárido local? uma análise da expansão da agricultura irrigada nas áreas beneficiadas pela obra hídrica

Abstract

Large-scale water diversion projects are designed to enhance water security and foster socioeconomic development in semiarid regions by supplying water to support the establishment of productive enterprises, with a particular emphasis on promoting irrigated agriculture. The Canal do Sertão Alagoano was designed so that 75% of its water volume would be allocated to agriculture. Thus, the objective of this study is to assess the changes that have occurred in irrigated agriculture based on land use and land cover in the areas already benefited by the construction of the canal. The research analyzed land use and land cover (LULC) changes in a 1,154 km2 (115,493 ha) area located between the municipalities of Delmiro Gouveia and São José da Tapera, which has already benefited from the Canal do Sertão Alagoano. The study area corresponds to a 10 km-wide strip of land (5 km on each side of the canal’s margins) along the 123 km of constructed canal. Two methods were used to generate LULC classification. The first method relied on pre-processed LULC data from the MapBiomas platform (2006–2022). The second method was based on LULC classification using the Random Forest model (2016–2022). Field visits to the municipalities of Delmiro Gouveia, Pariconha, Água Branca, Inhapi, and São José da Tapera allowed for the validation of the model's performance in identifying irrigated agricultural areas. During these visits, interviews were conducted with local farmers to understand irrigation dynamics and assess the impact of the Canal do Sertão on agricultural production in the Alagoas backlands. MapBiomas data presented a precision index above 90% for forest, natural pasture, non-vegetated areas, water bodies, and non-vegetal natural formation classes. However, these data showed low precision in identifying agricultural areas in the semiarid region of Alagoas. On the other hand, the Random Forest model demonstrated high accuracy in LULC classification. Nevertheless, field visits revealed some limitations of the Random Forest model. The results indicated a significant increase in irrigated agricultural areas in the regions benefited by the Canal do Sertão. In 2016, the irrigated agriculture area was 176 ha, according to the Random Forest analyses. By 2022, this area had expanded to 2,111 ha, representing an increase of 1,099% in just six years. Between 2014 and 2018, 49 water use permits for the canal were requested. In the following five years, from 2019 to 2023, the number of requests increased significantly, totaling 772 permit applications. These SEMARH permit data corroborate the increase in irrigated areas identified using the Random Forest model. The model exhibited high precision in detecting irrigated agriculture, though it faced limitations in lowland areas. Based on model data, SEMARH records, and field visits, an expansion of irrigated agriculture between 2016 and 2022 was observed. It is expected that the completion of the Canal do Sertão will further boost local agriculture, necessitating the support of public policies to ensure sustainability and the efficient use of water resources. Keywords: Survey of irrigated areas; Vegetation cover; Water resources; LULC; Random Forest.