Sea Surface Temperatures in the Nino Regions and Annual Precipitation in Equatorial Pacific Atolls.

Water resources in equatorial atolls are amongst the most vulnerable globally, partly because of extreme variability of annual precipitation (P) due to frequent ENSO events. IPCC projections for the central and western tropical Pacific indicate mean annual rainfall will increase as sea surface temperatures (SSTs) rise. Projections of the intensity and frequency of ENSO events and hydrological droughts are of low confidence. Here, relationships between 12-month May to April precipitation (PM-A) in two equatorial atolls, Tarawa and Kiritimati in Kiribati, and 12-month SSTM-A in the Nino regions surrounding the atolls are examined between 1950 and 2022. Only the Nino4 region has as significant temporal trend in SSTM-A. There are no significant trends in PM-A in either atoll due to large ENSO-related interannual variability. In both atolls, strong, highly significant correlations are found between PM-A and SSTM-A in the Nino regions eastward of the atolls. These show ∂PM-A/∂SSTM-A for both atolls over 1,000 mm/°C. The relationship for Kiritimati appears nonlinear. Comparison of ranked very much above normal (VMAN, percentile > 0.9) and very much below normal (VMBN, percentile < 0.1) SSTM-A with ranked VMAN and VMBN PM-A revealed poor correspondence for both atolls, suggesting that extreme SSTM-A are not a sole determinant of extreme PM-A. The nonlinearity of the relation is shown by ∂PM-A/∂SSTM-A for below normal PM-A being an order of magnitude smaller than trends for above normal PM-A.