Trends in sub-hourly, sub-daily and daily extreme rainfall events in eastern Australia

Intensity and frequency of extreme rainfall are expected to change in future due to anthropogenic climate change; however, this change may not be uniform across spatial and temporal scale. This paper examines the trends of sub-hourly, sub-daily and daily extreme rainfall events from 38 rainfall stations located in southeast Australia. Two non-parametric tests (Mann-Kendall and Spearman Rho) were applied to detect trends at 10, 5 and 1% significance levels. The sub-hourly (6, 12, 18 and 30 min) and sub-daily (1, 2 and 6 h) annual maximum rainfall events generally showed an upward (positive) trend. However, the longer duration rainfall events (12-72 h) generally showed a downward (negative) trend. It was found that stations showing positive trends were characterized by higher elevations compared with the stations showing negative trends. This finding has important implications for urban stormwater management in the near future as most urban stormwater systems operate on a smaller catchment scale where sub-hourly and sub-daily rainfall events are used in their design.