Dry days ahead spell double trouble

DRY: Freshly shorn sheep congregate in a holding area at a farm on Te Parae Rd, Masterton.PHOTO/ANDREW BONALLACK

BLAME the southern annular mode, or SAM to technical types. The big dry which has holidaymakers rejoicing and farmers on edge has links to a variable climate pattern which extends from the South Pole and whose oscillations affect our weather.

In its positive phase, the SAM is associated with settled weather and relatively light winds over New Zealand - as we've been experiencing since Christmas, says Professor James Renwick of Victoria University's school of geography, environment and earth sciences.

Its negative phase brings strong westerlies and unsettled weather to our latitude, says Renwick, a climate specialist formerly with Niwa. That's what we endured throughout spring, when temperatures were cooler than normal and many areas experienced higher than normal rainfall.

But the prevailing westerlies late last year meant low rainfall in eastern areas subject to a rain shadow effect - east of the Main Divide in the South Island and regions such as central Hawke's Bay and parts of Wairarapa.

In these districts, including Canterbury, Otago and Marlborough, it's been mainly dry since August and the high pressures which have brought warm, sunny days since Christmas have only worsened moisture levels in already parched soils. Renwick says the big anti-cyclones associated with SAM's positive phase tend to "park" themselves to the east of the country, diverting fronts and low pressure areas to the north and south of the country or causing them to dissolve.

Northerners wondering why a few weeks of sunshine can prompt rural angst need only recall the 2007/08 drought which covered much of the country and cost the economy $2.8 billion.

Renwick says the climate pattern is similar to 2007/08 and to the even-more-severe 2013 drought which browned-off the North Island and South Island West Coast.

He says drought is something we will need to get used to with climate change and there are implications for agricultural land use.

"There is likely to be a doubling of the frequency of droughts over several decades in the regions that are currently very dry." Climate change modelling shows a trend to drier conditions in eastern and northern regions over time, particularly during spring, he says. "We expect years that are quite dry will happen more frequently. One in 20-year events would become one in 10."

For a nation increasingly dependent on water-thirsty dairy farming, the adjustment may trickle down to all of us.

For now, council-imposed and voluntary water restrictions are affecting farmers dependent on irrigation in many areas, particularly dairy farmers already dealing with lower milk payouts who have dried off herds early, while the lack of grass has beef and sheep farmers feeding supplements or sending stock to meat works early. The tinder-dry conditions have stretched firefighters in Canterbury, Marlborough and Hawke's Bay and prompted fire bans. Garden hose restrictions are in place in the Waikato and Thames-Coromandel.

Though the Government says it's too soon to declare a drought - unlocking financial assistance for farmers - in the worst affected areas, Niwa's long-term climate outlook is for the dry conditions to continue at least until late-February. A front may bring rain to some areas around the middle of next week but may not offer more than a couple of days' respite.

"Potentially, if there is no significant rainfall for the next month or so, we could be heading into the one of the worst nationwide droughts we've seen for some time," Niwa principal climate scientist Dr Andrew Tait told NZME this week.

Niwa forecaster Chris Brandolino says northern areas may get some relief next week but "the eastern sides of both islands need easterlies to get any significant rainfall". Brandolino says several days of decent rain are needed to restore soil moisture levels and the best bet is a tropical low or cyclone from the north. There's a "slightly elevated" chance of an ex-tropical system swinging by in the cyclone season, with the highest risk between February and April.

But the farmers' plight is not yet nationwide, with areas that experienced high rainfall during spring having good silage stocks and soil moisture levels only now hitting critical.

Lincoln University this week warned Canterbury could be in for a repeat of the "hard" droughts last seen in the 1990s, before irrigation schemes which have ushered in land use conversion to dairy farming in much of the region.

But Opuha Dam, completed north-east of Fairlie in 1998, is running out of water and Federated Farmers has revived calls for the Government to pipe water from Lake Tekapo under Burke's Pass to support Mackenzie Country farmers, where swathes of tussock have been converted to pasture. A study last year ruled out the scheme as too expensive and environmental critics would welcome the removal of irrigation gantries.

Other irrigation schemes diverting water from Canterbury's braided rivers are equally environmentally contentious while, in central Hawkes Bay, a proposal to dam a tributary of the Tukituki River to extend irrigation has polarised the community over costs and ecological impacts.

But the Government continues to push irrigation to support dairy farming and water storage to combat climate change, earmarking $280 million to kickstart schemes. Primary Industries Minister Nathan Guy is fond of noting that only around 2 per cent of annual rainfall is captured in dams.

"We don't have a shortage of rain, it just falls at the wrong time and in the wrong place." Guy countered environmental critics this week, claiming the Canterbury irrigation schemes would ease pressure on groundwater and help to revive Lake Ellesmere-Te Waihora.

Renwick says water storage makes sense but notes that high costs and environmental consequences mean irrigation will not work everywhere and land use may need to change.

"I grew up in Canterbury and if someone had told me there would be a lot of dairy farms in 30 years' time I would have laughed at them. It's only because of irrigation that that's happened and I doubt it's sustainable in the long term.

"The agriculture sector may have to think about land use changes in future. Australians have a lot of experience cattle farming in what looks like a desert."

Some beef and sheep farmers tout the benefits of converting from pasture to legumes such as lucerne, which tolerate less surface water and can boost productivity. Marlborough farmer Doug Avery this week told National Radio of his success converting to lucerne on his arid farm near Lake Grassmere but conceded it was not a universal remedy. From first-hand experience, Avery is concerned at the emotional toll that drought can take on indebted farmers and will spread his message nationwide next month as part of the Resilient Farmer roadshow.