It never rains on Sunday: the prevalence and implications of untagged multi‐day rainfall accumulations in the Australian high quality data set

Abstract The perception prevalent in the literature that Australian rainfall records are reasonably uncontaminated by untagged weekend accumulations is reassessed. An objective probabilistic test for untagged accumulations is developed and applied to 181 gauges that have previously been identified as having high‐quality data suitable for long‐term analyses of climate change. As many as 102 of these gauges are found to contain hidden, untagged accumulations, and the overall prevalence of untagged accumulations in the high‐quality data set is shown to be only slightly less than that of tagged accumulations. A simple study simulating the effects of accumulations in the records of the high‐quality data set shows that, in records (or parts of records) with frequent accumulations, rainfall probability, mean wet‐spell length and mean dry‐spell length can be underestimated by as much as 24%, 34% and 18% respectively, and that the magnitude of the potential prediction error in these variables (and also in indices of rainfall intensity extremes) at a site shows strong dependence on the rainfall probability. Selected published studies on climate change are reanalysed to account for the presence of untagged accumulations and to show that significant changes in long‐term trends can be obtained for individual locations. Copyright © 2004 Royal Meteorological Society