Extreme rainfall deficits - a New South Wales case study

The attempt is made to integrate rainfall deficit intensity, duration, frequency and spatial distribution into one end-product. Monthly rainfall data are integrated into all possible events with 3, 4, 6, 12, 24 and 36 months duration, over the 80 years 1900-1979, for 79 stations in New South Wales, and then the individual events are expressed as percentages of the averages of the relevant period. The lowest percen-tage value of the twelve possible events beginning in each year is taken as an extreme event, and the probability or return period of such events is assessed by fitting the log-Pearson Type IH frequency distribution. The latter is used to construct maps of New South Wales showing the spatial pattern of rainfall deficit, for the six different durations mentioned above, for four different return periods — 2 years, 5 years, 10 years, 50 years. Return periods of selected deficits and durations are also mapped and the relationships between deficit intensity, duration and frequency are graphed for 10 stations, forming west-east transects across the northern and southern parts of the State.