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River Flows and Groundwater Levels Near Normal 

Posted By Jo Pentreath | December 15, 2020

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

The deluge in Napier and other parts of the region on the 9th November was enough to cast shade on the month’s average rainfall totals but that was then followed by frequent rain over the rest of the month.  The final November tallies across the region were well above normal.  The Heretaunga Plains and the region’s south coast received three times their average November rainfall, while most other areas were close to double their average. The Ruahine Range was one pocket where the comparison was modest, at 127%.

We’ve struggled with below average river flows for a number of months but finally we’ve turned a corner it seems.  In November they were near normal around northern Hawke’s Bay and rachet up as you head south. In the Ngaruroro River we saw double the long term mean and, would you believe, a mighty 700% of the long term mean at a Wallingford site in the south.

Another worry has been groundwater levels that have persisted through the year at low levels.  The latest measurements we have – and these were taken just prior to the 9th of November – show the majority of sites at near normal levels for the time of year on the Heretaunga and Ruataniwha Plains.  That can only get better after November’s rain.  Prolific rain has meant that soil moisture levels have spent much of the month around field capacity and a little dry spell wouldn’t actually hurt!  Temperatures followed suit and were also above average – daily minimums by more than 1°C.

As the La Niña event continues and sea temperatures remain warmer than usual around the country, the seasonal forecast models are unanimous in depicting near or above normal rainfall for us during summer, plus warmer than usual temperatures.   The wind flow is expected to be predominantly north-easterly due to higher than normal sea level pressures over southern New Zealand and to the east of our region and lower than normal to the northwest.  Metservice predict below normal rainfall for December, based on a bout of westerlies to start the month and anticyclones to follow, but the overall picture for summer otherwise appears promising for rain.

 

 

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