Scientists have reconstructed rainfall patterns in the southwest tropical Pacific for the period 850-1200 AD, finding a sustained dry interval that coincided with increased island populations. The isotopic composition of rainwater captured in sediment cores reflects precipitation amount; analysis of hydrogen isotopes in ancient mud from swamps and lakes allowed researchers to infer past rainfall. The study, involving the University of Southampton, the University of East Anglia and other institutions, examined sediment samples from Tonga and Samoa. Results indicate the driest interval in the region during the past 2,000 years, occurring between 850 and 1200 AD. Genetic data show a rapid population increase in Samoa around 1000 AD, suggesting demographic expansion during the dry period. Climate variability in the area is linked to the South Pacific Convergence Zone, which can shift on decadal to centennial timescales. The timing of the drought aligns with the earliest eastward settlement of islands such as Rapa Nui and the Marquesas. The findings imply that prolonged climate stress may have contributed to the eastward expansion of Polynesian societies, though the exact mechanisms remain under investigation.