Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 10 5 2006 10.5194/hess-10-769-2006 http://www.hydrol-earth-syst-sci.net/10/769/2006/ http://www.hydrol-earth-syst-sci.net/10/769/2006/hess-10-769-2006.html http://www.hydrol-earth-syst-sci.net/10/769/2006/hess-10-769-2006.pdf 769 782 2006-10-19 Investigation of dominant hydrological processes in a tropical catchment in a monsoonal climate via the downward approach L. Montanari lmontanari@arpa.emr.it M. Sivapalan A. Montanari DISTART, Faculty of Engineering, University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy Departments of Geography and Civil {&} Environmental Engineering, University of Illinois at Urbana-Champaign, 220 Davenport Hall, 607 S. Mathews Avenue, Urbana, IL 61801, USA formerly at: Centre for Water Research, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia This study explores the dominant processes that may be responsible for the observed streamflow response in Seventeen Mile Creek, a tropical catchment located in a monsoonal climate in Northern Territory, Australia. The hydrology of this vast region of Australia is poorly understood due to the low level of information and gauging that are available. Any insights that can be gained from the few well gauged catchments that do exist can be valuable for predictions and water resource assessments in other poorly gauged or ungauged catchments in the region. To this end, the available rainfall and runoff data from Seventeen Mile Creek catchment are analyzed through the systematic and progressive development and testing of rainfall-runoff models of increasing complexity, by following the "downward" or "top-down" approach. This procedure resulted in a multiple bucket model (4 buckets in parallel). Modelling results suggest that the catchment's soils and the landscape in general have a high storage capacity, generating a significant fraction of delayed runoff, whereas saturation excess overland flow occurs only after heavy rainfall events. The sensitivity analyses carried out with the model with regard to soil depth and temporal rainfall variability revealed that total runoff from the catchment is more sensitive to rainfall variations than to soil depth variations, whereas the partitioning into individual components of runoff appears to be more influenced by soil depth variations. The catchment exhibits considerable inter-annual variability in runoff volumes and the greatest determinant of this variability turns out to be the seasonality of the climate, the timing of the wet season, and temporal patterns of the rainfall. 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