Evidence of Secular Changes in Rainfall Data from the Tropical Western and Central Pacific over a 20-year Period

Abstract

Rainfall data from the tropical western and central Pacific over the period from 1971 to 1990 show both decadal and interannual variability. A statistically significant secular trend may be used to model the overall rainfall variability. However, locally weighted regression analysis reveals that this increasing trend stalls in the early 1980' s, and reverses its course by the year 1990. Decomposition of individual rainfall time series into low frequency, seasonal, and irregular components facilitates the isolation of the time varying annual cycle and the elucidation of the interannual signal. Strong or prolonged warm EI Nino-Southern Oscillation events dominate the interannual variability during the study period. The decadal scale variation in the annual cycle is so systematic, in fact, there is approximately a 20% reduction in its amplitude between 1971 and 1982. In addition, the long-term change in the seasonal component appears to modulate the much shorter-term interannual signal.