Tropical oceans drive Malawi's malaria risk

Transmission of malaria, one of the world's deadliest infectious diseases, is highly sensitive to environmental conditions. Understanding the large-scale climate patterns that influence these conditions is crucial for developing forecasting tools, which could be especially valuable for prevention in low-resource nations like Malawi. Previous research has often focused on statistical correlations between local weather and disease trends but has rarely explored the underlying physical climate mechanisms. Here we show that two distinct ocean-based climate patterns are the primary drivers of interannual malaria variability in Malawi. A warm tropical Atlantic leads to wet conditions in Malawi and increased malaria cases. In contrast, a warm Indian Ocean drives hot, dry conditions and reduced malaria cases. We find that soil moisture is the crucial link between these remote climate drivers and local disease dynamics, and looking ahead, future climate change is expected to reduce soil moisture levels in the country by 2100 (magnitude uncertain), which could reshape transmission patterns. By identifying these climate drivers and the physical processes that link them to disease outbreaks, our work provides a foundation for building physically grounded, reliable early warning systems.