Hydrological modeling of flow changes due to land use and land cover changes in the Ibicui River Basin

The way water resources behave in the face of changes in land use are essential for managing a watershed. The Ibicul river basin, located in the center of the state of Rio Grande do Sul, Brazil, has great agricultural potential and peculiar characteristics regarding its hydrological regime. Changes in land use and land cover with the purpose of expanding economic activities in this area can generate major impacts on the flow regimes of this watershed. This study shows an analysis of the influence of land use and land cover changes on the flow regime in the Ibicul river basin from the large-basin hydrological model (MGB-IPH), considering maps of land use history and vegetation cover in the study area. The results were used to analyze the changes in the maximum and minimum annual and monthly average flows. The efficiency of the model was evaluated by the Nash-Sutcliffe coefficient (between 0.636 and 0.801) for peak flows and by the Nash-Sutcliffe log (between 0.682 and 0.863) for recession flows, indicating high correlation and low volume error (-0.45 to -8.20%). The greatest change in land use was the forest coverage reduction associated with agriculture land use. As a result, an increase in the average monthly flows and in the reference flow Q90 was verified. In some sub-basins, a significant modification in the reference Q90 flow and maximum flow was verified. The Mann-Whitney test showed that the results were accurate. The results indicated that changes in forest coverage and land use have an impact in the flow regime in the Ibicul Watershed.