Significantly hot Waikato weather prompts check on low water flow restrictions

Low water levels in the Waikato River during a previous period of summer heat. Photo / Alice Rose Tiffany

Some Waikato region waterways are already experiencing lower flows than normal for this time of year due to significantly high temperatures and a lack of rain.

That's prompted Waikato Regional Council to call on water take consent holders to carefully check they are complying with low flow restrictions.

The council has also heard from some bore owners who are struggling to access water for stock due to falling groundwater levels.

Council water allocation team leader Donna Jones urged farmers to contact the council to discuss the options if the reduced availability of water for stock supply is becoming an urgent issue.

"A resource consent is required before any new bore is drilled or existing bore deepened," Ms Jones said. "But farmers should call us on 0800 800 401 in the first instance if urgent consent to drill is required."

The regional council says some bore owners are struggling to access water for stock. Photo / NZME

She said separate resource consent may also be required to take water depending on the proposed take location and volume required.

For waterways in parts of the region already starting to experience low flow conditions, Ms Jones reminded surface water take consent holders they had a responsibility to ensure compliance with their consent conditions.

"As the weather heats up and stream flows drop, there may be a requirement for consent holders to reduce or cease their take. The specific action required will depend on the low flow restriction conditions in the consent."

Ms Jones said low flow conditions of a consent will refer to an appropriate river flow monitoring station and low flow value. Current river levels should be checked against the consent. Regular water use records are also required, she said.

Farmers wanting to receive automated Hydrotel text alerts for Waikato Regional Council flow sites should email their mobile number and consent number to consent_data@waikatoregion.govt.nz.

Senior water scientist Bevan Jenkins said soil moisture levels are drier than the same date last year and much drier than the historical average.

"There are signs of climate change related water stress in a number of areas and this is being expressed as reduced water availability, which is placing increasing pressure on water users," Mr Jenkins said.

"There has been a year-on-year increase in groundwater bore drilling permits since 2016/17 and preliminary analysis shows increased total volumes of surface and groundwater take applications since 2008."

Mr Jenkins said streams in the South Waikato that are strongly groundwater fed are close to or are at record low flows for this time of year. This is due to the lower rate of precipitation recharging groundwater over recent years.

Groundwater resources in the Coromandel Peninsula are generally localised systems which experience different conditions and pressures. At the end of 2021, groundwater level measurements indicated a range of conditions – bores with close to record high levels, record low levels and average condition had all been recorded.

"Of course, the timing and intensity of rainfall events and antecedent soil moisture conditions will all play a role in how much precipitation recharges aquifers," Mr Jenkins said.

Regional resilience team leader Rick Liefting said there is no significant rain forecast over at least the next week. Tropical Cyclone Cody is heading down early next week, but there is still significant uncertainty on what if any rain might fall. Any significant rain from the weather system is likely to be short-lived and run off quickly with limited infiltration.

"Niwa's seasonal climate outlook predicts normal to below normal rainfall out to March, so any significant rain will likely be in the form of an intense weather system, rather than sustained periods of rain," he said.

Niwa's outlook summary says marine heatwave (MHW) conditions intensified in New Zealand's coastal waters during December. NZ's coastal sea surface temperatures ranged from 1.6C to 2.5C above average.

This is expected to continue to have a strong upward influence on air temperatures and humidity. For the northern North Island, the magnitude of the MHW surpassed the previous record-breaking event of summer 2017-18.

For the next three months as a whole, temperatures are very likely to be above average across the country. Warm nights and periods of high humidity will continue to be a factor.

Sub-tropical northeasterly winds and a lack of southerly fronts may mean that cooler than average temperatures occur quite infrequently. However, eastern areas of both islands may experience a reduction in hot days due to more frequent onshore winds.