On meteorological droughts in tropical Pacific Islands: time-series analysis of observed rainfall using Fiji as a case study

Analysis of historical droughts was undertaken by converting observed monthly rainfall over the period 1949-2008 to the Standardized Precipitation Index (SPI). The modified Mann-Kendall test applied on monthly rainfall showed statistically significant downward trends at significance level alpha = 0.01. The Sen's Slope, estimated from the time-series, revealed statistically significant decreases in annual rainfall ranging from similar to 13 to 47 mm year(-1). Based on the SPI, drought duration and severity was non-uniform across stations over the 60 year period. The strongest impacted stations were located in western and northern Fiji where rainfall deficiency for the period 1969-1988 led to a dramatic increase in moderate and severe droughts. The return periods of annual rainfall were much longer at these stations relative to those in outer-lying islands. While rainfall increased over the period 1989-2008, the actual amounts did not exceed 1949-1968 totals, confirming a net shift towards drier conditions since the 1950s. This study has demonstrated that SPI can be a useful tool for diagnosis and monitoring meteorological droughts in tropical Pacific islands. Copyright (C) 2010 Royal Meteorological Society