Regionalization of daily mesoscale rainfall in the tropical wet/dry climate of the townsville area of north‐east queensland during the 1988–1989 wet season

Abstract

AbstractThis paper describes the use of unrotated principal component analysis (PCA), various oblique rotated principal component (PC) solutions, and the VARIMAX orthogonal rotation scheme. One of the objectives is to determine which PC solution achieves the most satisfactory degree of “simple structure” in the distribution of PC loadings, based on rainfall data collected during the 1988–1989 wet season from a comparatively dense rain‐gauge network (in excess of one gauge per 25 km2) in the Townsville area of tropical north‐east Queensland, Australia. The Harris‐Kaiser Case II BTB rotation was subsequently judged to be the most appropriate PC solution for the total wet season record, and for subsets based on the three most frequently occurring synoptic circulations.Daily isohyetal maps and radar imagery are used to show that the rotated PCs could be physically interpreted. The PC loadings derived from the Harris‐Kaiser II BTB rotation were then used as input to the Ward clustering strategy for regionalization of the total wet season record. The interactions between different synoptic circulations and changes in the spatial patterns of mesoscale rainfall are discussed as a basis for understanding the regionalization of the 1988–1989 wet season. The analysis demonstrates the need for a longer period of record before precipitation affinity areas, or regions of relatively coherent rainfall, can be used for forecasting purposes. None the less, the work shows the inadequacy of using the official gauge site at the local meteorological office as representative of the region, and further highlights the importance of local topographical controls on the synoptic‐scale circulation for producing distinct spatial rainfall patterns. It is believed that this is one of the first studies attempting a regionalization of rainfall at a mesoscale within the tropics.