Characteristics and drivers of baseflow response in 183 Australian catchments

Abstract

Daily streamflow data for 183 Australian catchments were used to assess the characteristics and main drivers of baseflow and quick flow behaviour, and to find an appropriate balance between simplicity and explanatory performance in modelling. Baseflow separation was performed following the Wittenberg algorithm. A linear reservoir model (one parameter) produced baseflow estimates as good as those obtained using a non- linear reservoir (two parameters) and was therefore considered the more appropriate. The transition from storm flow dominated to baseflow dominated streamflow generally occurred 7 to 10d after the storm event. The catchments investigated had baseflow half-times of about 12 d, with 80% of stations having half-times between 7 and 34d. The shortest half-times occurred in the driest catchments and were attributed to intermittent occurrence of fast-draining (possibly perched) groundwater. Median baseflow index (BFI) was 0.45 with considerable variation between stations. Catchment humidity explained 27% of the variation in derived baseflow recession coefficients. Another 53% of variance in recession coefficients as well as in BFI showed spatial correlation lengths of 200 to 300km, corresponding to terrain factors rather than climate or land use. The remaining 16 to 20% of variance remained unexplained. Most (84%) of the variation between stations in average baseflow could be explained by monthly precipitation in excess of potential evapotranspiration. Most (70%) of the variation in average quick flow could be explained by average rainfall. Another 20% of variation was spatially correlated over spatial scales of 400 km, possibly reflecting a combination of terrain and climate factors; the remaining 10 to 16% remained unexplained.