Borda livre e segurança de barragens: da tradição metodológica ao desafio das mudanças climáticas

Abstract

This study investigated dam freeboard dimensioning methodologies, from their origins to contemporary practices, and assessed the impacts of climate change on these design criteria, with specific application to the conditions of the Brazilian semi-arid Northeast. To this end, a systematic literature review was conducted, identifying the evolution of approaches, key influencing factors, and knowledge gaps. Subsequently, a methodology integrating climate change scenarios into freeboard dimensioning was developed and applied, using the Arrojado Lisboa Dam (Banabuiú Reservoir) in Ceará state as a case study. The impacts of climate change on design parameters were quantified by contrasting results obtained from traditional methodologies (USACE, USBR, and ANA) with those derived from considering future climate scenarios. Future projections were analyzed using data from CMIP6 (Coupled Model Intercomparison Project Phase 6) climate models, considering two greenhouse gas emission scenarios (SSP2-4.5 and SSP5-8.5). The results demonstrated that traditional methodologies underestimate freeboard requirements by not adequately considering future climate changes. For the Arrojado Lisboa Dam, the current freeboard of 3.5 meters proved insufficient when confronted with climate change scenarios, which indicated the need for values between 5.01 and 7.05 meters. It was observed that changes in extreme precipitation patterns, rather than alterations in wind regimes, are the predominant factor for the increased freeboard requirement in the Brazilian semi-arid region, demanding standardized quantification in current guidelines. The comparative analysis revealed fundamental divergences among traditional methods, primarily attributed to different assumptions regarding design wind velocity definition and the supposition of a low probability of simultaneous occurrence of maximum flood and extreme wind. This work contributes significantly to the literature by integrating, for the first time in the Brazilian semi-arid context, the impacts of climate change on extreme precipitation and wind regimes in a unified methodological approach for freeboard calculation. The findings reinforce the urgent need to update regulatory guidelines for dam dimensioning, explicitly including the effects of climate change and the quantification of uncertainties.