Climate extremes and the dynamic reshaping of snail habitat: implications for the spatiotemporal heterogeneity of schistosomal vulnerability in Brazil.

Extreme climate variables are increasingly important for understanding the distribution of Biomphalaria snails, the intermediate hosts of Schistosoma mansoni. While many studies focus on long-term averages, our approach emphasizes the role of climatic extreme events and their seasonal timing in shaping habitat persistence. We applied spatially explicit Random Forest (RF) species distribution models with spatial cross-validation and bootstrap aggregation to produce robust and transferable predictions of snail habitat suitability, and then ranked the influence of extreme climate variables using SHapley Additive exPlanations (SHAP) values and partial dependence plots. The models performed well, with average area under curve (AUC) values of 0.75 across species and partial AUC ratios greater than one, confirming the robustness of the predictions. Precipitation seasonality, multi-month drought indices, surface absorbed solar radiation extremes, and diurnal air temperature range were the highest-ranked drivers, though their influence was not uniform across snail species. Biomphalaria glabrata was most responsive to seasonal recharge, while B. straminea showed resilience to variability and often persisted in man-made habitats. Biomphalaria tenagophila was more constrained by drought and radiation stress. Spatial comparisons between 1995 and 2020 indicated expansions and contractions in various states, with new hotspots emerging in southeastern and central Brazil, while habitat suitability declined in drought-prone regions, such as in the State of Pernambuco. These results demonstrate that climate extreme events, in addition to long-term baseline changes, drive the spatially heterogeneous redistribution of Biomphalaria habitats. Also, our findings highlight the need for species-specific monitoring, integration of water infrastructure management, and forward-looking surveillance strategies that address both climate variability and landscapes modified by humans.