Scoop has an Ethical Paywall
Work smarter with a Pro licence Learn More

Video | Business Headlines | Internet | Science | Scientific Ethics | Technology | Search

 

NIWA Calculates 1:200 Year Flood For Parts Of Canterbury

Preliminary analysis by NIWA climate scientists has shown that the recent Canterbury rainfall was so extreme in some inland places that it could be expected to happen only once every 200 years.

NIWA climate scientist Dr Trevor Carey-Smith says it was the long duration of the rainfall, over more than two days, rather than the short-term intensity which was exceptional.

The rain event happened from May 29-31. During that time Environment Canterbury’s rain gauge near Mt Somers recorded its largest 48-hour rainfall event totalling 526 mm. Just 10 km away, on the plains the other side of Mt Somers, another gauge recorded "only" 310 mm in the same period, also its largest ever total.

The first cut at analysing the rainfall data for the region from May 29-31 suggests that the 48-hour rainfall totals that were recorded at Mt Somers, Geraldine and Snowdon would all be expected on average only once every 200 years. These rain gauges span 100km south west to north east in inland Canterbury.

"These results show how widespread this event was, although it is interesting to note that the most extreme rainfall only occurred in a relatively thin strip along the Canterbury foothills," Dr Carey-Smith said.

Nearer to the coast, at places like Ashley, Oxford, Darfield and Methven, the 48-hour rainfall observed was lower and reduces the expected probability of the event occurring to about once in 50 years on average.

That dropped to once every 30 to 40 years for Christchurch and once every 10 years for Akaroa which recorded 250mm of rain over three days - a large amount but not unusual.

Advertisement - scroll to continue reading

Are you getting our free newsletter?

Subscribe to Scoop’s 'The Catch Up' our free weekly newsletter sent to your inbox every Monday with stories from across our network.

Dr Carey-Smith said that these calculations assume the probability of extreme rainfall has not altered during the past, when in reality we expect the likelihood of such events to increase due to climate change.

For example, a once in 200-year event estimated using historical observations corresponds to a 0.5% probability of occurring in any given year, but if we were to take climate change into account, we would expect these odds to increase.

River flood return intervals which respond to shorter-term rainfall intensities, are still being evaluated.

© Scoop Media

Advertisement - scroll to continue reading
 
 
 
Business Headlines | Sci-Tech Headlines

 
GenPro: General Practices Begin Issuing Clause 14 Notices

GenPro has been copied into a rising number of Clause 14 notices issued since the NZNO lodged its Primary Practice Pay Equity Claim against General Practice employers in December 2023.More

SPADA: Screen Industry Unites For Streaming Platform Regulation & Intellectual Property Protections

In an unprecedented international collaboration, representatives of screen producing organisations from around the world have released a joint statement.More

 
 
 
 
 
 
 
 
 
 
 
 

Join Our Free Newsletter

Subscribe to Scoop’s 'The Catch Up' our free weekly newsletter sent to your inbox every Monday with stories from across our network.