Historical Annual Rainfall Changes on the Central Coast of NSW: Further Evidence of Alternating Rainfall Regimes

Historical annual rainfall data for 16 long-term stations on the Central Coast of NSW show significant multidecadal periods of alternating high and low rainfall which we call, flood- and drought-dominated regimes. Rainfall was high between 1863 and 1900; low between 1901 and 1948; high between 1949 and 1990; and low between 1991 and 2008. CUSUMS are usually significantly different between each time period according to non-parametric statistical tests. Mean annual rainfall decreased by up to 22.4% between 1863-1900 and 1901-1948, increased by up to 38.2% between 1901-1948 and 1949- 1990 and decreased by up to 27.2% between 1949-1990 and 1991-2008. Spatial coherence of the rainfall changes throughout the Central Coast indicates that they are not the artefact of a change in the site, height, exposure or type of rain gauge but represent real changes in meteorological conditions, possibly connected to El Nino-Southern Oscillation events and/or Interdecadal Pacific Oscillation phases.