Hotspot Watch
A weekly update describing soil moisture across the country to help assess whether severely to extremely dry conditions
are occurring or imminent. Regions experiencing these soil moisture deficits are deemed “hotspots”. Persistent hotspot
regions have the potential to develop into drought.
Facts: Soil Moisture
Across the North Island, soil moisture levels have decreased almost everywhere during the past two weeks. The most
substantial decreases were observed in Northland, Auckland, northern Waikato, and the Coromandel Peninsula. Smaller
decreases also occurred in the Wellington region, southern Manawatu-Wanganui, and much of Taranaki. Meanwhile, small
increases in soil moisture levels were observed in western Bay of Plenty and the East Cape.
The driest soils across the North Island compared to normal for this time of the year are found in the Far North, while
the wettest soils for this time of the year are found in small areas of western and central Bay of Plenty. Hotspots are
now in place across nearly the entire eastern coast of the North Island, the Coromandel Peninsula, far northern Waikato,
Auckland, and all of Northland. In fact, soils in the Coromandel Peninsula, Auckland, and Northland are extremely drier
than normal.
Across the South Island, soil moisture levels have generally decreased in eastern areas while generally increasing in
western areas during the past two weeks. The most substantial decreases were observed in eastern and central Southland,
much of Otago, and southern Canterbury. Meanwhile, substantial increases were observed in western Southland. Smaller
increases occurred in Tasman as well as the Buller, Hurunui, and Kaikoura districts. The driest soils in the South
Island compared to normal for this time of the year are found from coastal Clutha district to interior Southland, while
the wettest soils for this time of year are found in far western Southland, western Tasman, and the far northern West
Coast. Small hotspots are in place from coastal to interior Otago as well as on Banks Peninsula.
Outlook and Soil Moisture
For much of the North Island, little rainfall is expected during the next week. Isolated showers may move through
western and southern areas over the upcoming weekend, but amounts will only be a couple millimetres. The same areas may
see additional light showers early next week (9th-10th January), but rain amounts will be no more than about 5 mm.
Regions such as Northland, Bay of Plenty, Gisborne, and Hawke’s Bay may see little if any rainfall during the next week.
With minimal rainfall expected across the North Island, soil moisture levels are expected to decrease nearly everywhere
in the next week. The large hotspots along the eastern coast and in the northern North Island will continue to
strengthen, and new hotspot areas will likely develop across central and southern Waikato and Manawatu-Wanganui.
For the South Island, a few showers will move across most locations on Friday (6th January), with generally 10-15 mm
along the West Coast and up to 5 mm elsewhere. Additional showers could produce up to 10 mm in Otago and southern
Canterbury on Saturday. Isolated showers will produce minimal rainfall early next week, with another storm possibly
bringing up to 25 mm to the West Coast on Wednesday (11th January).
Generally low rainfall in the eastern and northern parts of the South Island during the next week will likely lead to
further decreases in soil moisture levels, while increases will be possible along much of the West Coast. The current
hotspots on Banks Peninsula and in Otago may strengthen and expand during the next week, especially across southern
Canterbury and interior Otago. A new hotspot may also form in northern Marlborough.
Background:
Hotspot Watch a weekly advisory service for New Zealand media. It provides soil moisture and precipitation measurements around the
country to help assess whether extremely dry conditions are imminent.
Soil moisture deficit: 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: the difference between the historical normal soil moisture deficit (or surplus) for a given time of year and actual
soil moisture deficits.
Definitions: “Extremely” and “severely” dry soils are based on a combination of the current soil moisture status and the difference
from normal soil moisture (see soil moisture maps at https://www.niwa.co.nz/climate/nz-drought-monitor/droughtindicatormaps)