Frosts are directly a risk of the lessee but if the vineyard was poorly sited and protected then it could affect the lessee’s ability to pay their rent and the ultimate value of the vineyard.
As part of due diligence, frost protection was considered in detail. The following is a formal report from Stu Powell of Climate Consulting and some informal comments from Brian Woods of Sacred Hill Marlborough.
From Climate Consulting
The following brief overview summarises data from 3 Climate Towers at a property on North bank Road encompassing Bartletts Creek:
Initial data suggests frost will pose a risk to the proposed vineyard development. Coolest temperatures were found at the tower located furthest up the valley and temperatures appeared to warm toward North bank Road. A detailed frost profile has yet to be completed, but data suggests minimum temperatures are higher than those recorded at Climate Consulting’s reference Wairau Valley AWS located at Wairau Valley Township by 1.0 – 1.5°C.
Inversion strengths are strongest furthest up the valley (>2°) and weaken toward North Bank Road. This reflects increased air movement draining the Wairau Valley, as opposed to quite different drainage winds from the Bartletts Creek tributary. Wind machines could be expected to provide an effective means of frost protection from the majority of frost events, however, wind machine spacing should be tightened to no greater than 5ha / machine over northern-most (assuming) cooler areas of the property.
Wind drift speeds were light – moderate, although marked changes in drift direction were observed reflecting cool air drainage from a number of smaller contributing gullies and valleys. Wind direction frequency analysis performed as part of the full frost report will ultimately dictate numbers and positions of wind machines.
From Brian Woods of Sacred Hill
“It was a reasonable frost here this morning (9th of September) so I took the chance to take some temperatures at Bartlett’s. This morning the Wairau drift had stalled due to the strong southerly, this generally causes a harder frost in areas normally frost free such as Rarangi and Rapaura. The Southern Valleys were cold with – 2dg at Hells Gate and Singing Bridge for 6 hours (these are two other Sacred Hill vineyards in Marlborough). Hammond Est in Renwick was also -1.9dg for 2 hours.
The top terrace at Bartletts was positive 0.9dg dipping to 0.3dg with a drift down the valley of approximately 5 kph. The side gullies were 1.3dg, which is warmer than I expected.”
During development planning, the fan placement plan provided by NZ Frost Fans shows 3 fans covering the cooler part of the block at present. Adjustments can be made regarding placements once tree removal has been factored into the plan.