DARLING RIVERINE PLAINS BIOREGION Background Report

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16/08/02 Darling Riverine Plains Bioregion Background Report
Long term rainfall variation
Trends in available moisture resulting from the annual variation in rainfall are determined by
calculating the Cusum (cumulative residual mass) curves for Menindee, Mungindi, Trangie,
Walgett and Bourke. These curves (Figure 2.9) indicate that the rainfall was high throughout
the 1880s and 1890s but there was a steady decrease from about 1900 until 1948 with a
resultant moisture deficit throughout the bioregion. The severity and timing of this deficit
varied between the five locations. Since about 1950, the moisture availability generally shows
an upward trend although this was delayed until 1974 at Menindee and was not sustained at
Trangie from 1960 to 1974.
Cummulative Sums for Rainfall
Menindee Mungindi Trangie Walgett Bourke
Figure 2.9 Rainfall CuSums for five locations in the DRP
The rainfall within the DRP does not have a regular annual cycle and plant growth and animal
breeding patterns will be controlled by this long term pattern. This will influence the recovery
rates of particular habitats and populations, with the current upward trend in the rainfall
suggesting that conditions are favourable for potential re-establishment and recovery of
populations. This may help explain the increased growth of the unpalatable native shrubs or
‘woody weeds’ in parts of the bioregion.
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