IMPLICATIONS FOR PEAK FLOWS OF THE MARRECAS RIVER BASIN DUE TO CHANGES IN THE BRAZILIAN FOREST CODE

ABSTRACT Changes in the Brazilian Forest Code (BFC) have soften the criteria for recovery and conservation of permanent preservation areas (PPAs), enhancing processes related to surface runoff. The aim of this study is to understand the effects of changes in PPA classification criteria established by BFC of 2012 to the detriment of BFC from 1965 considering the surface runoff response in the basin draining the upper Marrecas River valley in the flow peaks. The HEC–HMS model was used to simulate flow peaks considering three land-use scenarios, representative of the current use, adapting it to PPAs fitted to the BFC of 1965 and 2012 and seven precipitation return periods. In the proposed scenarios, the use of BFC of 2012, to the detriment of that from 1965, would imply a PPA reduction from 44.5% to 13.7%, resulting in a 22.1% increase in the average flow peaks, not representing, however, a significant reduction in the flow peaks when compared to the scenario representing the current land use. Therefore, when compared to BFC of 1965, in the Brazilian new Forest Code PPAs were reduced by 69.2%, increasing peak flows by up to 30.7%, thus minimizing the legal possibilities of flood mitigation to the urban perimeter of Francisco Beltrão, Paraná State, Brazil.摘要 巴西森林法（Brazilian Forest Code, BFC）的修订放宽了永久保护区域（permanent preservation areas, PPAs）的恢复与保护标准，加剧了与地表径流相关的水文过程。本研究旨在探究2012年版巴西森林法所确立的永久保护区域分类标准变更（相较于1965年版巴西森林法）对马拉卡斯河上游流域径流峰值处地表径流响应的影响。本研究采用HEC-HMS模型，设置三类土地利用情景（分别代表当前实际土地利用、适配1965年版与2012年版巴西森林法的永久保护区域配置情景），并结合7个降水重现期，对径流峰值进行模拟。在所设置的情景中，采用2012年版巴西森林法标准（相较于1965年版）将导致永久保护区域占比从44.5%降至13.7%，平均径流峰值升高22.1%；但相较于当前土地利用情景，该情景下的径流峰值并未出现显著降低。因此，相较于1965年版巴西森林法，2012年新版巴西森林法下的永久保护区域占比下降了69.2%，径流峰值最高升高30.7%，这将削弱巴西巴拉那州弗朗西斯科贝尔特朗市城区周边通过法定途径实现防洪减灾的可能性。