The interannual variability in streamflow presents challenges in managing the associated risks and opportunities of water resources systems. This paper investigates the use of seasonal streamflow forecasts to help manage three water resources systems in south-east Australia. The seasonal streamflow forecasts are derived from the serial correlation in streamflow and the relationship between El Nino/Southern Oscillation (ENSO) and streamflow. This paper investigates the use of ENSO and serial correlation in reservoir inflow to optimise water restriction rules for an urban township and the use of seasonal forecasts of reservoir inflow to help make management decisions in two irrigation systems. The results show a marginal benefit in using seasonal streamflow forecasts in the three management examples. The results suggest that although the ENSO–streamflow teleconnection and the serial correlation in streamflow are statistically significant, the correlations are not sufficiently high to considerably benefit the management of conservative low-risk water resources systems. However, the seasonal forecasts can be used in the system simulations to provide an indication of the likely increases in the available water resources through an irrigation season, to allow irrigators to make more informed risk-based management decisions.

Introduction

Rainfall and runoff can vary considerably from year to year. The management of land and water resources involves designing and operating to cope with the variability in the climate system. Reliable forecasts of streamflow months in advance can improve the management of water resources systems. It is possible that seasonal streamflow can be forecasted from the serial correlation in streamflow and from the relationship between streamflow and El Nino/Southern oscillation (ENSO) in many parts of the world (Dettinger et al., 2000; Chiew and McMahon, 2002).

This paper illustrates some of the benefits of using seasonal streamflow forecasts to help manage three water resources systems in south-east Australia. The interannual variability of Australian (and South African) rivers are about twice that of rivers elsewhere in the world (McMahon et al., 1992), and this large interannual variability presents challenges in mana- ging the associated risks and opportunities of water resources systems in rural and urban environments.