Hydrological implications of the Southern Oscillation: variability of the rainfall-runoff relationship

A connection between El Nino Southern Oscillation (ENSO) and weather phenom ena in eastern Australia has been recognized for several decades. However. little work has been devoted to addressing how this correlation affects hyd rological system behaviour within regional scale catchments. In this study. spatially distributed ENSO effects are evaluated in terms of monthly rainf all, evaporation, streamflow and runoff characteristics for a 1300(2) km ca tchment. The catchment is located in southeastern Australia where previous studies have indicated only modest ENSO influences on rainfall variability. Spatial and temporal analysis indicates that strongest ENSO-induced rainfa ll variability occurs during summer months. Additionally, the: strength of the relationship is variable in space indicating that topographic controls may affect ENSO influences on rainfall totals and intensities. However, ana lysis of runoff shows substantially magnified ENSO-induced variability In c omparison to the induced variability in rainfall. This may be attributable to the nonlinearity of runoff generation. Differences in antecedent moistur e storage conditions will exist but mag also br enhanced by complementary E NSO influences on daily rainfall intensities and mean monthly evaporation a nd temperature totals. The degree of the nonlinearity displayed by the hydr ometeorological processes presented demonstrates that the significance of E NSO forecasts for surface water resource management should be assessed with direct regard to streamflow generation rather than on the basis Of rainfal l totals alone.