Dry Waingawa River in summer. PHOTO/FILE

Grace Prior
grace.prior@age.co.nz

Wairarapa still has the driest soil in the North Island and is the closest to falling into hotspot status.

National Institute for Water and Atmospheric Research [Niwa] said the moderate to heavy rain generally affected western areas of the North Island during the past week, while much less rain was observed along the east coast.

It said rainfall amounts were low in the eastern North Island, where Gisborne, Hawke’s Bay, and Wairarapa generally received less than 5mm.

“Amounts of 25mm to 50mm were common from Northland south to the Kapiti Coast, with some areas seeing more than 50mm. In addition, parts of southern Waikato, Taranaki, and the Kapiti Coast received 100mm or more during the past week.”

Niwa said this had resulted in moderate soil moisture increases across the upper and western North Island.

“Meanwhile, eastern areas saw soil moisture decreases, particularly in Wairarapa.”

“Currently, no official hotspots are located in the North Island, although coastal Wairarapa is nearing hotspot status.”

Niwa said a hotspot would be declared if soils became “severely drier than normal”, which occurs when soil moisture deficit was less than -110mm, and the soil moisture anomaly was less than -20mm.

It said a soil moisture deficit was the amount of water needed to bring the soil moisture content back to “field capacity”, which is the maximum amount of water the soil can hold.

“Soil moisture anomaly is the difference between the historical normal soil moisture deficit [or surplus] for a given time of year and actual soil moisture deficits.”

Niwa said its New Zealand Drought Index [NZDI] map showed that no dry conditions were seen in the North Island yet, as of November 15. The map also showed that no dry conditions were seen in the South Island either.

“In the South Island, hotspots have been put in place in coastal Hurunui, Selwyn, and Ashburton districts, while a previous hotspot in Waimate District dissipated in the past week.”

It said the driest soils in the South Island, when compared with normal for this time of the year, were found in parts of central Canterbury and coastal Southland, while the wettest soils for this time of the year were located along the West Coast and in parts of interior Otago.

Niwa said an area of high pressure will be in control through to at least Sunday morning for the North Island, leading to dry weather for most locations over the next few days.

“From late Sunday into Monday, a weak passing low may bring rain to the lower half of the North Island, with showers possible farther north.”

It said mostly dry weather would return beginning Tuesday with a few more showers for the lower North Island today and tomorrow.

Niwa said weekly rainfall totals could reach 15mm to 30mm across much of the southern half of the North Island, although confidence levels were a bit lower than usual due to the uncertainty of the rainfall.

“In the upper North Island, rainfall totals are likely to be lower, in the 5mm to 15mm range.”

It said that because of the expected rainfall this week, soil moisture levels were likely to remain generally constant or decrease slightly across the southern half of the North Island.

“Farther north, at least small soil moisture decreases are more likely.”

Niwa said there would continue to be a small chance that a hotspot may form in Wairarapa during this week, with no hotspots expected elsewhere.



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