Potential drought on horizon as El Niño brews
Growers in Tasman’s Waimea Plains, which holds some of the most fertile productive land in the South Island, are being warned to prepare for a potential drought as the forecast El Niño weather phenomenon approaches.
According to research carried out by Tasman District Council’s environmental data team, the 75-year rainfall record from Nelson Airport suggested that a very strong El Niño, which has been predicted, would increase the risk of a drier-than-normal year in the Waimea plains.
In the seven previous very strong El Niño years, annual rainfall was below the long-term average every time, with a typical year receiving about three-quarters of normal rainfall.
Monthly data show the same pattern – many months during very strong El Niño years were below normal, although wet months could still occur.
The timeline also shows that most past very strong El Niño events coincided with moderate, severe or extreme drought conditions.
Stephen D’Andrea, an environmental data scientist at the council, said this did not mean drought was guaranteed, but it did support early preparedness messaging around reduced rainfall, soil moisture stress and water-demand pressures for the region’s growers.
Horticultural consultant Greg Dryden, of Fruition Horticulture, said a drought would threaten shallow-rooted vegetable crops. Market gardens in the area – often described as the market garden of the South Island – were highly vulnerable.
“Something with a shallow root system has got much less resilience than something with a deeper root system,” he said.
Dryden said the looming dry spell underscored the critical role of the newly constructed Waimea Dam, which was catalysed by the region’s devastating 2000-2001 drought.
The dam served as a strategic buffer by supporting the Wairoa and Waimea rivers to recharge the underground aquifers that supplied local growers.
However, access to this water security depended on ownership. Commercial growers who bought shares in the dam were allocated water based on their soil and crop type.
“The risk is obviously very high for those that don’t have Waimea Dam shares, but fairly low for those that do have dam shares,” he said, noting that smaller growers who did not invest face the risk of “cease takes” or reduced allocations as the council enforced its restriction stages.
Tasman District Council’s communications and change manager Chris Choat said the council was already preparing for the dry conditions through its Dry Weather Task Force, an annual partnership with regional water management committees.
Choat said the Waimea Plains were a vital national asset.
“It’s a huge strategic area for produce,” he said. “It’s a very productive area – it’s one of the strategic horticultural areas in the country.”
While previous droughts, such as a severe dry spell in 2018, heavily impacted both agricultural and urban supplies, Choat emphasised that the current outlook remained a forecast.
“It’s a forecast full of confidence, but it is still a forecast,” he said, adding that the length of the dry period could not yet be determined.
Dryden said that a dry season could actually benefit permanent crops like grapes and apples by improving fruit flavours and avoiding harvest-period rain. He advised growers to watch techniques used by Australian farmers to cope with extreme dry spells.
“Growers are pretty resilient, pretty adaptable, but you can’t deny that there’s some risk associated with a very dry year, and people need to be prepared,” he said.
By Andy Brew, Nelson Mail
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