The Tropical South Pacific (TSP) contains over 5,700 islands and a vulnerable population of around 10 million people, 57% of whom live within 1 km of the coast. Freshwater availability and food security depend on rainfall generated by the South Pacific Convergence Zone (SPCZ), the largest convergence zone in the Southern Hemisphere. Variations in SPCZ location and strength drive seasonal to centennial changes in precipitation, influencing droughts, flooding, cyclone pathways, ecosystem resilience, and the ability of Pacific Island nations to meet Sustainable Development Goals. Historical evidence also links prolonged rainfall changes to island abandonment, migration, and shifts in agricultural practices.

Understanding long-term SPCZ variability is limited by the scarcity of high-resolution palaeoclimate records. Existing precipitation proxies are geographically restricted, often discontinuous, and generally shorter than 600 years, while instrumental observations span less than a century. Current evidence suggests SPCZ rainfall responds to remote climate modes including the Interdecadal Pacific Oscillation, Atlantic Multidecadal Variability, and Southern Annular Mode, but available data are insufficient to test mechanisms or validate climate models.

This project generated a network of quantitative precipitation reconstructions spanning the SPCZ over the past 3,500 years, combined with with climate model experiments to identify how large-scale climate variability drives SPCZ rainfall. This provides fundamental new understanding of past and future hydroclimate change across the Tropical South Pacific.