Climatic and physical factors that influence the homogeneity of regional floods in southeastern Australia

The identification of hydrologically “homogeneous” regions is a primary step in many regional flood frequency techniques. Although statistical procedures for identifying homogeneous regions abound in the literature, there has been relatively little effort directed toward the identification of the physical and climatic basin characteristics that cause similarity in standardized flood peak distributions. We use regional flood peak and basin characteristics data for 104 basins in southeastern Australia to investigate the physical and climatic factors associated with the statistical distributions of flood peaks; the degree of geographical coherence of homogeneous regions; and the extent to which information on flood peak statistics is encapsulated by the physical and climatic characteristics of basins that are commonly used in regionalization studies. Our results show that (1) membership of a particular homogeneous region is determined largely by a combination of climatic characteristics that is related to runoff generation; (2) supergroups consisting of sites within aggregated homogeneous regions that have reasonably similar flood responses show some degree of spatial coherence; and (3) the basin characteristics that influence regional homogeneity can be identified despite the use of indices that smooth spatial and temporal variability.