PDP were engaged by Auckland Council to review all rainfall, flow and soil moisture data from their current and historic network to determine the return period of the Auckland Anniversary event (27 January 2023). Extrapolating HIRDS V4 shows that this event had a return period in the order of a 1,000 to 10,000 years which is unlikely given there are only 150 years of measurement.
PDP created a statistical model to explain rainfall depths across the Auckland Region by applying Bayesian inference to 15 million rainfall records (all instantaneous and daily data) across more than 70 rainfall gauges and over forty flow recorders. From this, uncertainty estimates of annual maxima were obtained for every location in the Auckland region, from 1862 to present day. With the Bayesian sampling technique Markov-Chain Monte Carlo, the uncertainty of these annual maxima estimates is integrated in the extreme value statistics. This approach significantly increases the accuracy in the range of extreme events compared to using standard extreme value analysis using short term records from individual rainfall sites only.
Key Contact
