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Four Consecutive Months of Below Rainfall

Posted By Jo Pentreath | April 15, 2021

Dr Kathleen Kozyniak
Pri
ncipal Scientist Air
Hawke’s Bay Regional Council

March rainfall clocked up a concerning statistic.  The Heretaunga Plains, Ruataniwha Plains, the region’s south coast and both the Kaweka Range and Ruahine Range have recorded four consecutive months of below normal rainfall.  We normally start worrying at three.  The March totals didn’t even reach 50% of the month’s average and rainfall accumulations at some sites, for the hydrological year to date (July to June), are behind where they were this time last year – our most recent drought period.

March river flows were lower than average and we’re still very much in the mode of monitoring low flows when we expect to be winding down by now.  Soil moisture was below median levels for March and in some places, like Bridge Pa and Crownthorpe, the levels fell into or came close to hitting the lowest 10th percentile of readings. The majority of measured wells had groundwater levels that were in the below normal or lowest ever category.  Soil temperatures on both the Heretaunga and Ruataniwha Plains ended the month near average on 19°C.

We’re transitioning from a La Niña event to neutral conditions, though our pattern of weather will be slow to change according to the forecasts for April to June.  Seasonal models still persist with higher pressures to the south and east of New Zealand and lower to the northwest.  Easterlies therefore continue to feature highly so a bout of westerlies during mid-April may be more of an aberration than the norm.  On the whole it doesn’t bode well for rainfall because that same pattern hasn’t delivered a lot since November.  There is a vague chance pressures might be lower over the country in May which provides a glimmer of hope that we may get near normal rainfall over the three month period.  Temperatures are expected to be near or above average.

 

Percentage of Normal Rainfall

         

 

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