Long range forecasting of low rainfall

Strong relationships have been developed between a global parameter, the so uthern oscillation index (SOI), and a more local parameter, the geopotentia l height (GpH), in one season and precipitation in the next season. These r elationships, which have only been examined for part of eastern Australia a t this stage, explain > 50% of the variance in one-season ahead precipitati on for areas up to 500 000 km(2) and > 80% of the variance for smaller area s. The relationships, which are essentially simple linear regressions betwe en precipitation in the target season and GpH or SOI in the previous season , apply when a third variable is in a particular range during the previous season. The success of this forecasting scheme is apparent in all four seas ons of the year. This form of forecasting, which is based on the partitioni ng of observed data, has the potential to provide reliable 3-months ahead f orecasts of precipitation for large regions. Copyright (C) 1999 Royal Meteo rological Society.