Big wet is one for the ages

18:44, Apr 30 2014

Christchurch has endured its wettest March and April since records began in 1864.

Tropical cyclones and stubborn rainstorms have left the city water-logged.

A rain gauge in the Christchurch Botanic Gardens recorded 324.7mm of rainfall from the start of March to April 18. That record-breaking figure does not yet include the recent rainstorms.

The nearest rival to that figure is the 306.5mm of rainfall for March and April combined in 1951.

Once the approximately 70mm of rainfall from the most recent storm are included, the figure for March and April is likely to break the 400mm mark. That would mean about four times more rain had fallen in those two months than the 150-year average of 104.3mm.

National Institute of Water and Atmospheric Research climate scientist Gregor Macara said the Christchurch rainfall was "remarkable".


"It is already three times higher than the average with more rainfall to come," he said.

"The rain has tended to come in quite large events rather than being spread across the two months. That is probably why it has caused such widespread flooding. The ground is already saturated so it is just inundated when there is more heavy rainfall."

MetService meteorologist Daniel Corbett said Christchurch had been hit by two tropical cyclones and a "stubborn" weather system in March and April.

There was a "stubborn low" over the east coast of the South Island in early March, and Cyclone Lusi in the middle of March and Cyclone Ita in mid-April brought "heavy and intense rain", he said.

"It is because we have had a couple of tropical systems, that are much more loaded with moisture, and a couple of slow-moving weather systems."

The rain gauge in the Botanic Gardens recorded 197.1mm of rainfall for March, compared to a 150-year average of 51.3mm, and 127.6mm for the first 18 days of April, compared to a 150-year average of 53.9mm for the whole month of April.

The Press