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Severe Drought Finally Breaks

Current status in early July 2003

The severe drought that struck much of New Zealand during the summer and autumn of early 2003 has broken. River flows, lake levels, and groundwater levels were at record or near-record lows over much of the country in March and April, except for northern regions of the North Island and some Canterbury foothills rivers. With a return to more normal rainfalls in many places in May and June, many rivers have begun to recover, but groundwater aquifers still need more rain. At the beginning of July, the national hydroelectric storage levels were slightly above the average for this time of year.

River flows were very low through to the end of April in the central and lower North Island, and in most of the South Island. Restrictions on taking water from rivers were in place for more than 60 rivers nationwide. Many rivers and lakes recovered well in May and June, especially in the central North Island and the west of the South Island, in response to higher rainfall. Rivers in coastal Otago and central Southland remain unusually low for this time of year. At the opposite end of the spectrum, there was serious flooding in Northland, Coromandel, Golden Bay and Nelson.

Groundwater levels were very low in Hawke’s Bay, Manawatu, Wairarapa, Wellington, Nelson, Marlborough, and Canterbury, and in some places they are still at historic low levels.

Algal blooms were a plague in some rivers and shallow lakes in many parts of the country during late summer and early autumn, as a result of the low flows and warm water temperatures. However, as temperatures have dropped, these problems have largely improved. Noxious weed growths continue in many areas such as Lake Wanaka, and new incidents of infestations have occurred in the Ahuriri arm of Lake Benmore. This has caused concern for Regional Councils and groups such as Fish and Game, NZ.

Outlook for July-September 2003

NIWA’s National Climate Centre predicted earlier this month that river flows for July-September would be normal, except in the east of New Zealand, where normal or below normal flows are expected, and in the west and south of the South Island where normal or above normal flows are expected.

However, even with normal rainfall in July-September, there would not be enough water in some key groundwater storages. Aquifer levels on the east coasts of the North Island and South Island are likely to be average or below average at the beginning of next spring, and some regions may face pressures on their resources over summer.

No major water quality problems are expected for lakes and rivers during July-September, except for the possibility of unseasonal, green algal blooms in rivers with extended periods of low flows.

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