Diagnostic analysis of water balance variability: A comparative modeling study of catchments in Perth, Newcastle, and Darwin, Australia

A comparative study is performed to explore interactions between climate variability and landscape factors that control water balance variability in three diverse regions of Australia: Perth (temperate with distinct dry summers); Newcastle (temperate with no distinct dry season); and Darwin (tropical region affected by monsoons). This comparative analysis is carried out through adoption of a common conceptual model. The similarity and differences between the three catchments are explored through evaluation of signatures of streamflow and soil moisture variability, and systematic sensitivity analysis with respect to parameters representing various landscape characteristics. The results of the analysis show that the biggest contributor to the differences between the catchments is the distribution of soil depth and the soil's drainage characteristics. The second factor is climate, as exemplified by the (annual) climatic dryness index and the intra-annual (seasonal) variability of both rainfall and potential evaporation, and associated rainfall intensity patterns, and their interactions with the soil properties (i.e., soil depth and the soil's drainage characteristics). In Perth and Darwin, climate seasonality is responsible for a seasonal switching on/off of subsurface stormflow at the start/end of the wet season, respectively. In Newcastle, where soil moisture contents hover near the field capacity value throughout the year, subsurface stormflow occurs frequently throughout the year, with event-based switching on/off in response to individual storms of moderate magnitude and temporal clustering of small storms. In addition, in rare circumstance, surface runoff is triggered in response to extreme storm events and temporal clustering of moderate to large storm events.