Environmental disruptions and malaria dynamics: causal evidence from climate extremes and fires in the Amazon

Abstract This study examines the causal effects of droughts, unusually high annual precipitation, and fire exposure on malaria incidence in the Brazilian Amazon using a staggered difference-in-differences approach. Combining municipal-level data from 2007 to 2021, we exploit variation in the timing of exposure to climatic and environmental shocks to estimate their dynamic impacts on malaria outcomes. The results show that droughts and unusually high annual precipitation are associated with reductions in malaria incidence, although the effects are not immediate and unfold over time. In the case of unusually high annual precipitation, the negative impacts are persistent across several periods, suggesting sustained disruptions in transmission dynamics. For fire exposure, the results indicate an immediate reduction in malaria incidence, followed by a more heterogeneous dynamic pattern, with some subsequent periods exhibiting positive effects. The analysis also reveals substantial heterogeneity across cohorts and calendar time, indicating that the magnitude and significance of the effects depend on when municipalities are first exposed and on broader temporal conditions. Robustness checks using alternative control group specifications, threshold variations, and placebo tests confirm the stability of the findings and support the validity of the identification strategy. These results contribute to the literature by providing causal evidence on the role of climatic and environmental shocks—rather than average conditions—in shaping malaria dynamics in a highly vulnerable region. The findings highlight the importance of accounting for non-linear and time-varying effects when assessing the health impacts of environmental change.