Flooding and water-availability impacts future global limits of Plasmodium vivax malaria

Plasmodium vivax is the most geographically widespread malaria parasite, with billions of people at risk of transmission. While malaria is now largely regarded as a tropical disease, historically, P. vivax extended far into temperate regions, including Europe and North America. Its distribution is strongly influenced by hydroclimatic conditions, particularly surface temperature and the availability of standing water for mosquito breeding. Today, international travel and trade occasionally introduce the parasite into non-endemic regions, and future climate change could amplify these risks and shift viable transmission zones.

Previous global estimates of malaria suitability often relied on precipitation as a proxy for surface water availability, neglecting hydrological processes and oversimplifying both present-day conditions and future projections. Here we extend our previous work on P. falciparum transmission in Africa and present hydrologically informed global estimates of P. vivax transmission suitability using a multi-model ensemble of climate and hydrology simulations. By explicitly incorporating hydrological processes, we identify river corridors as key areas of suitability, aligning with historical observations of malaria transmission patterns. This approach provides a more realistic representation of water availability compared to precipitation-based models.

Our findings indicate that future warming will reduce thermal constraints on transmission, particularly in northern latitudes, expanding potential P. vivax suitability into temperate regions. Europe, North America and Asia show future net increases in transmission suitability and a sensitivity to emissions pathway. However, when hydrology is considered, water availability emerges as a critical limiting factor under future climates. Regions such as southern Europe and western North America are projected to become increasingly water-limited, restricting transmission potential. This trend is absent in precipitation-only models. Conversely, areas with persistent or extreme flooding may experience heightened receptivity, suggesting that outbreaks could become more closely associated with hydrological extremes in the future. With more hydrological extremes projected, this finding places greater emphasis on the role of flood events in driving future P. vivax outbreaks. Such integration of both climate and hydrology in malaria suitability assessments can help inform malaria surveillance strategies and public health planning in both endemic and non-endemic regions.