Intensification of subhourly heavy rainfall

Area of Science:

• Climatology
• Extreme weather events
• Hydrology

Background:

• Previous research on climate change impacts on precipitation primarily focused on daily rainfall totals.
• Subdaily extreme rainfall events are challenging to detect and model due to their localized nature and short duration.
• Flash flooding is a significant hazard often triggered by short-duration, high-intensity rainfall extremes.

Purpose of the Study:

• To investigate trends in subhourly extreme rainfall near Sydney, Australia.
• To determine if subdaily rainfall extremes are increasing at a faster rate than hourly or daily extremes.
• To assess the consistency of observed trends across different data sources and account for natural climate variations.

Main Methods:

• Analysis of 20 years of rainfall data near Sydney, Australia.
• Utilizing data from multiple independent ground-based weather radars to track storms.
• Comparison of radar data with rain-gauge measurements to validate findings.
• Statistical analysis to identify trends and rule out natural climate variability.

Main Results:

• A robust positive trend of at least 20% per decade in subhourly extreme rainfall was identified near Sydney.
• No significant trends were observed in hourly or daily extreme rainfall during the same period.
• The observed subhourly rainfall trend was consistent across radar and rain-gauge data.
• The trend did not appear to be linked to known natural climate variations.

Conclusions:

• Subhourly extreme rainfall events are increasing significantly faster than those on longer timescales.
• The findings highlight a potential underestimation of flood risk associated with short-duration, high-intensity rainfall.
• Further research is needed to understand the drivers of these intensified subhourly rainfall extremes and their broader implications.