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River Flows Getting Low

Posted By Jo Pentreath | February 14, 2021

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

The past two months haven’t quite gone to the La Niña plan.  January rainfall was below normal, roughly 57% of the long-term average. It follows a dry December for all except northern Hawke’s Bay.   Two months of below normal rainfall has cut river flows off at the knees and low flows are proliferating.  We’re steadily eroding the buffer that November gave us.

Groundwater levels ended December measuring mostly near or above normal – a terrific result that seemed a long time coming.  Come the end of January and the below normal portion put up more of a fight.  Soil moisture levels sat above or on median levels for January on the Heretaunga and Ruataniwha Plains but dipped below median levels at Crownthorpe and other parts of the region.

The top January temperature surpassed 35°C and overall the daytime temperatures were a good 1°C above average – great for those in holiday mode. Soil temperatures on the Plains spent the month in the mid to low twenties.

The La Niña continues, though a transition to neutral conditions is expected through autumn.  It’s fair to scoff at previous promises of La Niña rain based on the results of the past two months.  The forecast models aren’t so unanimous in that promise this time around.  While they stick with the general pattern of weather they’ve depicted in the past few months, they aren’t necessarily equating it with high rainfall.  Higher than normal sea level pressures to the south of the country, lower than normal to the northwest and associated easterlies remains in their forecasts.  But it’s reasonable to expect an unchanged weather pattern to give an unchanged result, i.e. not as much rain as we’d like.

Potential still lies in a tropical cyclone outlook that suggests we could see an ex-tropical cyclone come our way by the end of April. Plus cyclone activity lingers about the Pacific Islands during the first half of February, the remnants of which we hope come our way.

 Percentage of Normal Rainfall

 

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