Tropical oceans drive variability in soil moisture and malaria in Malawi

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. We analyze malaria incidence alongside observational, reanalysis, and modeled climate data to identify the mechanistic link between climate and malaria variability in Malawi. Here, we show that two distinct ocean-based climate patterns drive interannual malaria variability in Malawi via their influence on local climatic and surface hydrologic conditions. 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 reduces 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. Malaria is a disease spread by certain mosquitoes that thrive in particular habitats affected by climate. This study shows that soil moisture is the key link between climate and malaria in Malawi, as wetter soils can create more standing water, which provides habitat for mosquito larvae. Distant oceans influence these soil conditions by triggering climatic chain reactions that affect weather in Malawi: a warm Atlantic Ocean leads to wetter soils and more malaria cases, while a warm Indian Ocean brings hotter, drier conditions and fewer cases. These climate-malaria relationships can be used to develop malaria forecasts to better predict and prevent outbreaks. Elling et al. investigate links between large-scale climate phenomena and malaria incidence in Malawi. They find that the tropical Atlantic and Indian oceans drive malaria variability in Malawi through downstream impacts on soil moisture.