Transient development or extractive cycle? A causal analysis of the Belo Monte Dam’s impact on population and labor dynamics in the Brazilian Amazon

This study contributes to the debate on the causal relationship between population dynamics and socioeconomic development by investigating the impact of the Belo Monte Hydropower Plant (BMHP) on the formal labor markets and social welfare of the Brazilian Amazon. Using a robust quasi-experimental Difference-in-Differences (DiD) design combined with Propensity Score Matching, we isolate the causal effects of this mega-infrastructure project on directly impacted municipalities (Altamira and Vitória do Xingu) compared to a synthetic counterfactual. Our findings identify a significant but ephemeral "boom-bust" cycle. While there was a sharp increase in formal employment and real income during the peak construction phase (2011–2016), these gains failed to persist in the long term, resulting in post-construction economic stagnation and high sectoral concentration. Furthermore, the analysis reveals a "development paradox": despite investments exceeding 31 billion reais, the project yielded statistically insignificant causal improvements in critical social indicators, such as infant mortality, school dropout rates, and healthcare infrastructure. By contrasting these results with similar extractive cycles in the Madeira River (Porto Velho), we demonstrate that large-scale energy projects in the Amazon often foster transient economic impulses rather than sustainable regional development. This research provides vital empirical evidence for population studies, arguing that without governance and effective public policy, such infrastructure leads to "social sediment" rather than lasting improvements in human well-being.