March 2007

• Rainfall: Extremely wet in Northland at the end of the month, with devastating floods; below normal in the east
• Soil moisture: Severe deficits in eastern regions from Gisborne to Marlborough, as well as Central Otago
• Temperature: Above average in most regions, especially Canterbury and Otago
• Sunshine: Above average in the east

Historical daily rainfall records were swept aside in eastern parts of Northland as exceptionally high rainfall rates produced widespread flooding and extensive infrastructure damage. There were a number of other climate extremes with electrical storms and hail, high winds, and a tornado. The Northland event stands in marked contrast to the rest of the month: March was a summer-like month, with a mix of anticyclones and winds from the northerly sector producing warmth and plentiful sunshine, and mainly dry conditions in the east.

Rainfall ranging from 250 to over 400 mm occurred in eastern Northland over the 28–29^th March. This was due to a stationary high pressure centre east of New Zealand preventing the progress of a band of heavy rain in a trough projecting humid northeasterlies across eastern Northland. This produced the most disastrous floods in the Northland region for many decades in the Far North and Whangarei districts, especially in the Bay of Islands area. Some buildings were washed away and homes flooded and many motorists were stranded on flooded roads. Initial estimates put the cost of damage from the floods up to $80 million. Of this, about $20 million is for damage to roads, clearing slips, and fixing bridges. The other $60 million includes damage to property and infrastructure, including stormwater and sewerage systems. Stock and losses of agricultural production have also occurred in low-lying areas.

The Northland floods marred what was a remarkably warm, dry, and sunny month overall. The national average temperature was 16.6 °C (0.9°C above normal), with temperatures at least 1°C above average in Auckland, Wellington, and parts of the east of both islands. In many regions, daytime maximum temperatures were noticeably above normal (more than 2.5°C above normal in parts of Wairarapa, Marlborough, and Canterbury). The month’s rainfall was 200 to 300 percent (twice to three times) of normal in Northland (due to the end of month floods), and also above normal in parts of Auckland, Thames-Coromandel, the central North Island plateau, parts of Buller and North Westland, and Southland. However, rainfall was low, being 25 percent (a quarter) or less of normal in parts of Gisborne, Hawke’s Bay, and Marlborough, and below normal rainfall in other eastern regions. The relatively dry weather meant that severe soil moisture deficits (of at least 130 mm) occurred in many eastern regions from Gisborne to Marlborough, as well as Central Otago, while significant soil moisture deficits (at least 110 mm) affected other eastern regions, as well as parts of the Kapiti Coast and Wellington. Temperatures were above average throughout much of New Zealand, especially in the east, being least 1.5 °C above average in parts of Canterbury and Otago. March was also a sunny month, especially in the east, with Gisborne and Blenheim both recording one of their sunniest March’s on record. Anticyclones (‘highs’) were more frequent than normal east of the North Island, resulting in more frequent northwesterlies than usual over much of the country.

Other Highlights

• Extremely high rainfall totalling over 400 mm occurred in eastern parts of Northland resulting in severe flooding on the 28–29^th. These amounts fell in eastern Northland in the area from Kaeo, to the Bay of Islands and just south of Whangarei. The two-day rainfall totals were amongst the highest on record for the area.
• There were also several other high rainfall events, between the 6^th and 17^th on the West Coast of the South Island. Flooding occurred in Westport on the 17^th, along with slips and road closures.
• The highest temperature during March 2007 was 32 °C recorded at Darfield on the 5^th, and Culverden on the 24^th. The lowest air temperature during the month was –1.0 °C recorded at Mount Cook Village on the 15^th.
• Unseasonable snowfall occurred at Lake Rotoiti on the 14^th.
• Damaging winds, with gusts, exceeding 130 km/h, were measured in Auckland during westerly gales between the 13^th and 15^th of March. Winds blew over grape vines in part of Marlborough on the 14^th.
• Damaging winds attributed to a tornado occurred in Stratford on the 21^st.
• Lightning strikes resulted in power outages to many homes in the Wellington region over the night of 13/14 March. A thunderstorm, with heavy rainfall, hail, and high winds affected the Christchurch district on the 18^th.
• Auckland was the warmest, Dunedin the driest, and Wellington the sunniest, of the five main centres. Rainfall was above normal in Auckland and Hamilton, and below normal in the other main centres. Temperatures were above normal in all five main centres. Sunshine hours were near normal in Auckland and Hamilton, and above normal in Wellington, Christchurch, and Dunedin.

Rainfall

Rainfall was 200 to 300 percent (twice to three times) of normal in Northland (due to the end of month floods), and also above normal in Auckland, Thames-Coromandel, the central North Island plateau, parts of Buller and North Westland, and Southland. In contrast rainfall was 25 percent (a quarter) or less of normal in parts of Gisborne, Hawke’s Bay, and Marlborough, and 50 percent (half) or less of normal in parts of Wellington, and Central Otago. Rainfall was also below normal in Wairarapa, Nelson, and North Canterbury.

Temperature

Mean temperatures were above average throughout much of New Zealand. However, they were at least 1.0 °C above average in Auckland, Wanganui, Manawatu, and many eastern regions, and at least 1.5 °C above average in parts of inland Canterbury and Otago. Temperatures were near average in the Far North and on the West Coast.

Sunshine

March sunshine hours and/or solar radiation were more than 110 percent of normal in the east from Gisborne to Otago, and near or above normal in most other parts of New Zealand.

Full report

• Full details of the  March 2007 Climate Summary

For further information, please contact:

Dr Jim Salinger – Principal Scientist, Climate NIWA National Climate Centre – Auckland Phone +64 9 375 2053 [email protected]

Stuart Burgess – Climatologist NIWA National Climate Centre – Wellington Phone +64 4 386 0569 [email protected]

Geoff Baird – Communications Manager Phone +64 4 386 0543 [email protected]

Acknowledgement of NIWA as the source is required.