A study of the changing climate in the US-Affiliated Pacific Islands using observations and CMIP5 model output

Abstract

This exploratory research examines the impacts of changing climate on the vulnerable US-Affiliated Pacific Islands (USAPI) from the perspective of the Intergovernmental Panel on Climate Change's (IPCC) Fifth Assessment Report (AR5) coupled with General Circulation Models (GCMs). Island-wide projections of future climate change (e.g. temperature, rainfall, and net water flux) were made using the latest IPCC AR5 GCMs protocol (Coupled Model Intercomparison Project Phase—CMIP5) with 38 GCMs with up to 105 model runs. A review was also made of studies on model-based future projections of the El Niño–Southern Oscillation (ENSO). The CMIP5 model's results clearly illustrate that the past trend in temperature (1950–2017) is rising while the rainfall trend remains more or less static. It is also clear from the projections that the long-term trend for temperature rise is fast and significant, while the trend for rainfall and net water flux (P-E) rise appears to be slow and marginal. On the perspective of CMIP5 model's evaluation for the USAPI region, the temperature projections are found to be promising, while the rainfall projection potentials, despite some limitations, are also encouraging. The prime concerns for future disruptions in the USAPI region are the consequences of increasing frequency of the ENSO and related rainfall activities. The long-term warming signal may further complicate the problem. Therefore, the currently water-stressed islands and low-lying atolls in the Federated States of Micronesia (FSM) and Republic of Marshalls Islands (RMI) are particularly vulnerable to El Niño-related heat stress or drought and La Niña-related inundations or flooding. In both cases, the future demand-oriented climate-sensitive water resources sector will be severely affected. A climate-information-based comprehensive water resources management plan (for the 2030s) is therefore essential with more detailed ENSO-related climate information and impacts in terms people can understand and respond to.