Abstract: Sub-daily rainfall intensity has a significant impact on runoff and erosion rates in northern Australian rangelands. It is therefore important to accurately represent sub-daily rainfall intensity in rangeland systems models (e.g. GRASP), which are used to investigate management impacts on runoff and soil erosion processes. We describe a new equation to calculate daily maximum 15-minute rainfall intensities (I15) for any location in Australia, using readily available daily rainfall and climate data. The new I15 model accounted for 46% (P < 0.01) of the variation in observed daily I15 for an independent validation data set derived from 67 Australia-wide pluviograph stations and represented both geographical and seasonal variability in I15. The model also accounted for 70% (P < 0.01) of the variation in the observed historical trend in I15 for the full record period (average record period was 37 years) of 73 Australia-wide pluviograph stations. The new I15 equation represents a significant improvement on the existing equation incorporated in GRASP, which needs to be calibrated for a given location.