Long-term variation of rainfall erosivity in Sydney | The Meteorological Society of New Zealand

Long-term variation of rainfall erosivity in Sydney

B. Yu

To establish the long-term trend and characterise the temporal variation of rainfall erosivity, which is needed to determine the rainfall-runoff factor in the Universal Soil Loss Equation, three models using annual, monthly and daily rainfall amounts to estimate annual rainfall erosivity were compared for Sydney. Annual and monthly rainfall amounts explain less than 50% of the variation of annual rainfall erosivity and the model using daily rainfall amounts in excess of 12.7 mm explains 79% of the variation of monthly erosivity values. The daily model was used to reconstruct an annual time series of rainfall erosivity for the period 1860 to 1992 using actual rainfall erosivity values for the period from 1922 to 1987. Examination of the annual rainfall erosivity values for Sydney showed that rainfall erosivity has significantly (at 0.05 level) increased at a rate of 75% of the mean per century for the period from 1922 to 1987 although the concurrent increase of rainfall at a rate of 24% of the mean per century does not have the same level of significance. For the period since 1949, both rainfall erosivity and rainfall amount were significantly higher in terms of the mean and interannual variability by comparison with the period from 1922 to 1948. Severe storms have increased in both magnitude and frequency of occurrence. Although the significant temperature increase in Sydney for the period from 1922 to 1987 at a rate of 1.4-A.33ºC/century is a likely cause of an increase in rainfall intensity, hence rainfall erosivity, there is no convincing explanation of this dramatic increase in the rainfall erosivity.

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