Pacific Rainfall over Millennial Scales (PROMS)

The Tropical South Pacific (TSP) is a vast area of ocean containing over 5000 small islands supporting a vulnerable human population of c.10 million of which 57% live within 1 km of the coast. All life on these islands depends on reliable precipitation for the provision of freshwater and food security, meaning that changes in the location and intensity of rainfall can result in damaging and costly societal impacts via droughts and flooding, with historical evidence of island abandonment and population migration.

Within the TSP, over 10 million people and sensitive ecosystems on the 5700 isolated Pacific islands depend on rainfall from the convective processes generated in the South Pacific Convergence Zone (SPCZ), which is the largest convergence zone in the Southern Hemisphere, and influences regional, hemispheric and global climate, and in turn is influenced by ENSO and other remote modes of climate variability. Movement and strength of SPCZ convergence results in seasonal, interannual and longer term change in precipitation which are linked to severe droughts, cyclone paths resulting in impacts on Pacific island nations ability to meet Sustainable Development Goals, and in the past drove periods of mass human migration.

In the last 1000-years, sustained periods of lower rainfall are thought to have contributed to the abandonment of some Atoll islands and the decision to migrate east into the Pacific. In other islands, changes in rainfall led to the development of different styles of agricultural system. However, compared to other parts of the earth, there is comparatively limited information about past precipitation changes in the TSP, in part because of a historical lack of suitable proxies and archives for producing high resolution, continuous records.

Proxies for precipitation reconstructed from sediments or stalagmites are limited to marginal areas to the SPCZ and are also short (