Climate Update 52 - October 2003

October

Climate

River flows

Soil moisture

Three-month outlook

Checkpoint

Backgrounder

Backgrounder

A drought index based on river flows
Roddy Henderson, NIWA
Catchment Proccesses and Water Resources

Figure 1: River flows for the Selwyn River in Canterbury, representative of the South Island east coast. The RDI reached a peak of almost 6 at the start of 1999, highlighting the major drought of 1998–99 and its relative severity.
Click to enlarge

Figure 2: Flows from Lake Wanaka between 1970 and 2002, representative of flows through the major South Island hydro-electric stations.

Checkpoint

Outlook and outcome – July 2003 to September 2003
From July to September, temperatures were near or below average in most regions, which was lower than expected. The expected cold snaps, snow, and inland frosts eventuated with a very frosty July.
Rainfall was as expected in most areas, but it was wetter in the eastern North Island and drier in the northern South Island and Waikato.
River flows were lower than expected in the west of the North Island and the north of the South Island, and higher than expected in the east of the North Island.

Climate

New Zealand Climate
A stormy start to spring
September was a month of extremes with stormy and unsettled conditions throughout the country. There were frequent days of westerly gales with a top wind gust of 176 km/h on 18 September at South West Cape, Stewart Island.
Very wet, especially in central and eastern districts
It was much wetter than normal, especially from Gisborne to north Otago in the east, and in Taranaki, King Country, and Wanganui in the west. Wanganui recorded its highest September rainfall since records began in 1890.

October

Climate Update is a summary each month of New Zealand's climate, including soil moisture and river flows.
October 2003 – Number 52
September’s climate: September was wild and wet, warm in the north and cool in the south.

River flows

New Zealand river flows
Flows were above normal for all North Island rivers, apart from some streams in Northland, Coromandel, and Bay of Plenty. South Island streamflows were above normal in Nelson, Buller, north and mid Canterbury, and western Southland. They were below normal in eastern Southland and south and Central Otago, and normal elsewhere.

Soil moisture

Soil moisture
Soil moisture levels at field capacity in most places
Soils were generally at field capacity, and in some eastern areas, there were water surpluses. Soil moisture deficits remained in South Canterbury and North and Central Otago, but conditions improved in coastal Marlborough.

Soil moisture deficit in the pasture root zone at the end of September (right) compared with the deficit at the same time last year (centre) and the long-term end of September average (left). The analysis is done for an average soil type where the available water capacity is taken to be 150 mm.