Avaliação do comportamento hidrológico da Bacia de Serra Azul-MG sob cenário hipotético de uso do solo com a adoção de sistemas agroflorestais

Abstract

The growing demand for natural resources has caused intense changes in land use around the world, with frequent removal of vegetation cover. Such transformations produce changes in the hydrological cycle processes, affecting water availability in terms of quality and quantity. In order to mitigate the impacts of changes in land use and cover on water resources, soil and water conservation practices have emerged, including Agroforestry and Syntropic Agriculture Systems (SAFs). The present study aims to investigate the effects of adopting SAFs on hydrological processes in the context of a rural basin. Scientific literature is still poor in studies of this kind. However, some studies indicate that the implementation of SAFs leads to reductions in surface runoff rates and sediment production, as well as increasing infiltration and base flow rates. In the present work, in order to investigate these effects, two methodologies were adopted: (1) a systematic review of the literature focused on empirical and hydrological modeling works that evaluate the influence of SAFs on the water balance, with special attention to works that describe the strategies adopted to represent SAFs in the SWAT model (Soil & Water Assessment Tool); (2) hydrological modeling applied to the Serra Azul reservoir watershed, Minas Gerais, using the SWAT model and simulation techniques for comparative land use scenarios. In the literature review, 310 publications relevant to the theme were obtained, including: 251 works in English and 59 in Portuguese. From this total, 56 cited or focused on the effect of SAFs on the water balance and only 11 presented different methodologies for representing hypothetical scenarios with the adoption of SAFs in the SWAT hydrological model. In the absence of a specific typology of land use to represent SAFs in the SWAT model, the subdivision of other types of land use available on the SWAT basis was adopted, containing the parameterization of mixed crops, weighting the percentages of area for each cultivation based on the percentages of areas occupied by the stratification of canopies (top of the tree) of each agricultural, shrub or forest species that make up the SAFs arrangements. In order to analyze the effect of SAFs, hypothetical scenarios of gradual implementation of SAFs in the basin area under study were compared. Through the results of hydrological modeling, it was verified that in scenarios with gradual adoption of SAF areas (9.17% to 25.76%), there were changes in some components of the water balance and in water and sediment production: reduction (average flow produced: 0.57% to 2.47%; surface runoff: 4.62% to 26.01%; peak flows: 3.39% to 8.20%; sediment production: 5.34% to 50.50%) and increase (subsurface lateral runoff: 4.27% to 14.44%; percolation: 0.49% to 4.77%; aquifer contribution: 1.58% to 7.08%; evapotranspiration: 1.08% to 7.08%; drought flows: 0.18% to 1.3%). Such results found in the present work and in existing works in the literature indicate that, despite the small reductions in average water production observed, SAFs have the potential to influence the components of the water balance and reduce erosion processes, favoring the maintenance of ecosystem functions associated with water and soil in watersheds.