Updated analysis of gauge-based rainfall patterns over the western tropical Pacific Ocean

Abstract

This work considers observed changes in tropical Pacific Ocean rainfall amounts and the influence of climate variability cycles upon them. Observations were taken from the Comprehensive Pacific Rainfall Database (PACRAIN), using strict data selection criteria of >99% data completeness from eight locations for the period 1971–2017. These data were used to analyze temporal and spatial rainfall patterns based on several indicators that considered rainfall amount and frequency, 95th percentile extreme rainfall events, and length of consecutive rain/drought events. These indicators were also computed using satellite-derived observations from the Global Precipitation Climatology Project (GPCP), as a means to compare gauge-based values with nearby estimates from the GPCP product. Results show a temporal pattern that tended towards a reduction in rainfall amounts and frequency across the tropical Pacific Ocean. The impact of phase changes of the Interdecadal Pacific Oscillation (IPO) was also examined. There was some evidence of the impact of the IPO, as well as of the El-Niño Southern Oscillation (ENSO), when seasonal and monthly trends in these indicators were analyzed. Comparison of the temporal patterns observed from the rain gauges with the trends computed using the GPCP estimates showed inconsistencies that varied considerably when comparing trends calculated at different island locations. Future work should consider further comparison of GPCP and gauge-based rainfall trends, as well as the attribution of climate change and other climate variability cycles to these trends.