Linking climate variability, topography, and health: SACZ–ENSO influences on leptospirosis in Minas Gerais, Brazil

Rainfall extremes during the austral summer frequently trigger floods in Brazilian cities and are strongly associated with leptospirosis outbreaks. This study investigates how the South Atlantic Convergence Zone (SACZ) and its modulation by the El Niño-Southern Oscillation (ENSO) influence precipitation anomalies and disease incidence in Minas Gerais (MG), Brazil. Atmospheric circulation during active SACZ phases (DJF) was analyzed using synoptic fields of moisture divergence, vertical velocity, and wind divergence. Results show that interannual and intraseasonal variability strongly modulate precipitation extremes, particularly in southeastern MG. The geomorphology of this region, characterized by steep slopes and deeply dissected valleys, amplifies SACZ-related convection and accelerates runoff, creating favorable conditions for disease transmission. During El Niño years, SACZ displacement southward enhanced localized rainfall anomalies, while La Niña years intensified continental SACZ activity and widespread convection, still concentrating cases in the southeast. Two case studies (2003 and 2012) confirmed the role of SACZ-ENSO interactions in driving both floods and leptospirosis outbreaks. These findings underscore the importance of integrating climate information, topography, and health surveillance to improve early-warning systems and adaptation strategies under climate change.