Hawke’s Bay Regional Council’s monthly public climate briefing today noted the drier than expected summer we've just experienced, with an outlook for normal rainfall during autumn.
"The significant rainfall events in December, January and February kept groundwater levels up, partly because less water was used for irrigation. Despite this, recent dry weather in the Heretaunga area has led to a decline in river levels," said Dr Stephen Swabey, HBRC Science Manager.
HBRC air quality scientist Dr Kathleen Kozyniak added, “Although much of the region saw near normal rainfall totals for February, the headwaters of our larger rivers weren’t as lucky. Rain tended to bypass the main ranges. The sea surface around New Zealand stayed warmer than usual through February so temperatures were balmy, and that should continue. An El Niño focussed in the central Pacific might actually be upon us after wavering for some time and NIWA advises normal to below normal rainfall totals for autumn.”
Soil moisture levels around the region were well above normal for most of summer, thanks to the season’s wet start, but are now close to expected levels for the time of year.
Groundwater levels in Hawke’s Bay typically reach their annual lowest points in late summer or early autumn.
In previous years we have seen a trend to lower summer levels over time. However this year groundwater levels have remained relatively elevated due to rainfall over November, December and January which has reduced the pumping demand from the aquifer system.
“In February, groundwater levels continued their normal seasonal decline, but in most wells levels have stayed normal to above normal. Our telemetered wells indicate the greatest rate of decline was in February in the Ruataniwha Plains. We can expect groundwater levels in both the Heretaunga and Ruataniwha Plains to begin rising in the next couple of months,” says Simon Harper, senior groundwater scientist.
“River flows across the region have been mostly below or close to normal during February. The rivers respond more quickly to dry or wet periods than groundwater,” says Rob Waldron, Hydrologist. The NIWA climate outlook forecasts river flows to be low or near normal through to April.
The Regional Council’s website now shows river and groundwater levels, with a map showing whether rivers are rising or falling, and more detailed data on a weekly, monthly or annual basis.
The Regional Council science team also reports on water use in the region, based on the high level of water metering and reporting through consents monitoring. This reporting includes water use by industry, irrigation, and domestic supply.
Across Hawke’s Bay, December’s overall water use was the lowest since 2012. October’s water use was the highest since 2012. Overall water used was less than the last 6 years. The TANK area (Tutaekuri, Ahuriri, Ngaruroro and Karamu catchments) used less than the minimum in February. The Tukituki area was in the average water use range.
11 March 2019
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