Historical changes in extreme precipitation events in the tropical Pacific region

Historical changes in tropical Pacific rainfall are analyzed using data from the newly enhanced Comprehensive Pacific Rainfall Database (PACRAIN), a daily rain-gauge database for the Pacific that contains almost 800 sites, some with records dating back to the 1800s. After a complete analysis of the database, 24 stations were selected to examine rainfall changes from 1971 to 2000 using daily data. In addition, a series of extreme event indicators, such as the percent of annual precipitation that falls on days exceeding the 99th percentile, were selected and analyzed in accordance with the World Meteorological Organization (WMO) guidelines for analysis of extreme events. Historical precipitation records in the central and southwestern tropical Pacific showed a trend towards decreasing precipitation during the period 1971 to 2000. This is consistent with previous research on changes from 1971 to 1990, as well as previous results that use data from a different set of stations. There was an increase in the characteristics of extreme precipitation events in most locations, even in those with a decrease in overall precipitation. This could have significant impacts in a hydrological sense, and illustrates the need to use extreme event variables when analyzing climatic patterns. Longer-term patterns were revealed through an analysis of monthly data from 14 stations over the period 1951 to 2004. Results suggest that the role of the Interdecadal Pacific Oscillation (IPO), especially the positive phase, could be important in explaining a significant amount of the observed changes.