Drought in the south-west Pacific: monitoring, prediction and future changes

Abstract In the south-west Pacific, where sweeping island chains and atolls cradle diverse cultures and ecosystems, drought can have catastrophic impacts on local communities. In this study we apply a multivariate drought monitoring framework using principal component analysis to satellite rainfall, a blended soil moisture product and reanalysis potential evapotranspiration over 1980–2018. These multivariate grids are paired with probabilistic seasonal rainfall forecasts to create drought early warning categories, facilitating the identification of ‘windows of action’ between an early warning signal and peak drought severity. Our analysis supports the hypothesis that early warning action windows of 3–5 months are possible for impactful drought periods in the region. We pair this early warning insight with projections guidance using an ensemble of dynamically downscaled CMIP6 models. We report on both quantitative and qualitative changes to future annual, dry season and wet season rainfall using a process-based framework that partitions the ensemble according to shifts in the South Pacific Convergence Zone and Asian-Australian Monsoon. This allows for the derivation of storylines which can be used by decision makers to plan decisively where projected changes are consistent and adaptively where they vary. Reporting on gridded drought monitoring, forecasting and projected future change has not been consistently evaluated for these Pacific Island domains before. As climate change intensifies and drought onsets against a backdrop of other extreme events, planning proactively at a range of short- and long-term timescales will be critical to preserving the cultural, ecological and social vitality of south-west Pacific Island communities.