Saturday, March 9, 2024

South Island Soil Moisture patterns & New Zealand Drought Index (NZDI)

Soil moisture anomaly (mm) at 9am on 07/03/2024 [NIWA]



Hotspot Watch 8 March 2024



A weekly update describing soil moisture patterns across the country to show where dry to extremely dry conditions are occurring or imminent. Regions experiencing significant soil moisture deficits are deemed “hotspots”. Persistent hotspot regions have the potential to develop into drought.

Recent rainfall and current soil moisture conditions:


South Island:

  • Rainfall amounts of 40-100 mm affected the West Coast and Tasman in the past week, with a few areas receiving more than 100 mm.
  • Although Southland received 25-40 mm, the upper and eastern South Island saw generally meagre rainfall amounts of 5-15 mm.  
  • This resulted in moderate soil moisture increases along the West Coast, but the east coast generally saw small additional decreases.   
  • The driest soils across the South Island, when compared to normal for this time of the year, are found across parts of Canterbury, while the wettest soils for this time of the year are found in western Southland.  
  • Hotspots are currently located across much of the upper and eastern South Island, including eastern Tasman, Nelson, parts of Marlborough, a majority of Canterbury, and eastern Otago.
  • As of 6 March, the New Zealand Drought Index (NZDI) map below shows that abnormally dry conditions are currently found in eastern Tasman, Nelson, Marlborough, northern and far southern Canterbury, and eastern Otago. Very dry to extremely dry conditions are located in Nelson, Marlborough, northern and far southern Canterbury, and northern Otago.  

Soil moisture anomaly (mm) at 9am on 29/02/2024 [NIWA]



Soil moisture anomaly (mm) at 9am on 07/03/2024 [NIWA]


Pictured above: Soil Moisture Anomaly Maps, relative to this time of year. The maps show soil moisture anomalies over the past two weeks.


New Zealand Drought Index (NZDI) 

As of 6 March, the New Zealand Drought Index (NZDI) map below shows that abnormally dry conditions are currently found in Northland, Auckland, part of the Coromandel Peninsula, eastern Bay of Plenty, much of the lower North Island, eastern Tasman, Nelson, Marlborough, northern and far southern Canterbury, and eastern Otago. 

Very dry to extremely dry conditions are located in eastern Northland, far southern Manawatū-Whanganui, Wellington, Nelson, Marlborough, northern and far southern Canterbury, and northern Otago. 

Please note: some hotspots in the text above may not correspond with the NZDI map. This difference exists because the NZDI uses additional dryness indices, including one which integrates the rainfall deficit over the past 60 days. Changes are therefore slower to appear in the NZDI compared to soil moisture anomaly maps that are instantaneously updated.




New Zealand Drought Index (NZDI) - 6 March 2024 [NIWA]


The week ahead:


South Island:

  • Other than a few showers in Southland on Friday night, high pressure will bring dry weather to the South Island through Sunday (10 March).  
  • A front will bring moderate to heavy rain to the lower West Coast on Monday, followed by a stronger front from late Tuesday to Wednesday (12-13 March) that will bring at least some rain to a majority of the South Island, including heavy rain for parts of the West Coast.
  • Scattered showers may return by next Friday (15 March).  
  • Weekly rainfall totals of 75-125 mm are possible in the lower West Coast, with 40-75 mm in the upper West Coast.
  • While Southland may again see moderate weekly totals of 25-40 mm, rainfall amounts of 10-25 mm are likely across much of the upper and eastern South Island.   
  • Due to the expected rainfall in the next week, additional soil moisture decreases are possible in the upper and eastern South Island, but the lower West Coast and Southland may 
  • The current hotspots in the upper and eastern South Island could strengthen and expand at least slightly in the next week, but the changes may not be substantial.

NIWA.

Pigeon Post News, Richmond.

  • NIWA Communications.

Pigeon Post News, Richmond.

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