NIWA's Hotspot Watch

NIWA's Hotspot Watch

Friday, 25 September 2015

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

Drought conditions were experienced last summer and autumn for many areas of the eastern South Island, while severely to extremely drier than normal soil conditions were observed for much of the North Island for much of last summer through to early autumn of this calendar year.

For the North Island, as we exit the traditionally higher rainfall months of winter, soil moisture levels are near to above normal for this time of year for much of the island. The exception, where drier than normal soils exist for this time of year, is eastern parts of the Bay of Plenty. Widespread and heavy rainfall over the past several days has brought wetter than normal soil moisture levels for this time of year for much of the Hawke’s Bay.

South Island soil moisture levels are much drier to severely drier than normal for this time of year for northeast Otago as well as for northern and southern sections of eastern Canterbury. For the rest of the island, near normal soil moisture levels are present, with a pocket of wetter than normal soils for this time of year in central eastern Canterbury, from Christchurch southwest to just north of Timaru.

Outlook

For the North Island, no significant change in soil moisture is anticipated over the next several days. It’s likely that rainfall amounts for the next week will be near or below normal for most of the island with near or above normal rainfall likely for eastern areas of the North Island from Wairarapa through to Gisborne.

For the South Island, no significant change in soil moisture is likely for areas along and west of the Divide as weekly rainfall will most probably be near normal or above normal. East of the Divide, soil moisture levels are likely to remain near current levels or decrease, as weekly rainfall is expected to be near normal or below normal. However, there are some indications that pockets of above normal rainfall may occur over the Otago region as well as for far northern areas of eastern Canterbury.

Consequently, a hotspot exists in far northern Otago through to southern sections of east Canterbury with another hotspot in north-central parts of east Canterbury, roughly north of Christchurch and south of Kaikoura.

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)

ENDS

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