Forgotten storms of the past: extreme rainfall events in New South Wales during the 19th century

Australian studies of daily rainfall extremes are often confined to the 20^th century due to data limitations prior to 1900, leaving gaps in our understanding of earlier climate variability. The aim of this study was to capture the spatio-temporal evolution of widespread extreme rainfall event and understanding how many minimum numbers of station observation we need to do so, during the 19^th Century. Here we focus on the region west of the Great Dividing Range in New South Wales, where we have a number of long weather records collected by early settlers. This region encompasses vital catchments that supply fresh water to millions, sustaining agriculture and is home to over 70% of Australia’s threatened species.

We use digitised instrumental records from the Bureau of Meteorology dating back to 1858 to identify widespread extreme rainfall events.  The main challenge faced during the study was the quality and sparsity of data across the study region. Adaptive kernel density estimation was applied to convert individual rainfall data points into density plots.  Trajectories for widespread extreme rainfall event was extracted. Dynamic time warping technique was used to determine the minimum numbers of station observation.

In this presentation, I will provide more detail of this new methodology, including the novel approach we took to factor in the impact of changing station network density.