Tasman Crop Met Report

Met Report

Table 1: Blenheim Weather Data – August 2011

August August 2011 August Period August 2011 compared LTA of LTA 2010 to LTA

GDD’s for month -Max/Min¹ 18.1 109% 16.6 (1996-2010) 25.0

GDD’s for month – Mean² 38.9 114% 16.6 (1996-2010) 37.5

Growing Degree Days Total

Jul – Aug 11 – Max/Min 23.2 87% 26.6 (1996-2010) 26.8

Jul - Aug 11 – Mean 57.0 101% 56.7 (1996-2010) 52.7

Mean Maximum (°C) 14.6 +1.1°C 13.5 (1932-1980) 14.6

Mean Minimum (°C) 2.2 -0.8°C 3.0 (1932-1980) 5.5

Mean Temp (°C) 8.4 equal 8.4³ (1932-200) 10.1

Mean Temp (°C) 8.4 -0.5°C 8.9³ (1986-2009) 10.1

Grass Frosts (<= -1.0°C) 17 1.6 more 15.4 (1932-1980) 5 6.2 more 10.8 (1986-2009)

Air Frosts (0.0°C) 8 0.4 more 7.6 (1932-1980) 1 4.0 more 4.0 (1986-2009)

Sunshine hours Sunshine hours – lowest

235.0 133% 177 (1935-2000) 155.8 129.2 1941 Sunshine hours – highest 2011 Sunshine hours total – 2011 1536.8 99% 1545.0 (1930-2000) 1471.4 Rainfall (mm) 52.6 82% 64 (1930-2000) 83.2 Rainfall (mm) – lowest 4.6 1969 Rainfall (mm) – highest 172.1 1990 Rainfall total (mm) -2011 425.0 95% 446.0 (1930-2000) 549.8 Evapotranspiration – mm 68.6 144% 47.6 (1996-2010) 47.3 Windrun (km) 218.1 89% 245.7 (1996-2010) 207.1 Mean soil temp – 10cm 5.2 -1.2°C 6.4 (1986-2010) 9.0 Mean soil temp – 30cm 7.2 -1.2°C 8.4 (1986-2010) 9.8 ¹GDD’s Max/Min are calculated from absolute daily maximum and minimum temperatures ²GDD’s Mean are calculated from average hourly temperatures ³Mean temperature for two long-term average periods provided as a contrast

Sunshine Hours

August 2011 has entered the record books as the sunniest August on record for Blenheim for the 82 years 1930-2011. August recorded 235 hours sunshine, beating the previous highest total of 225.8 hours recorded in 1972. The only down-side re the sunshine was that Nelson managed to record 12 hours more than Blenheim for August. Nelson is now 44 hours ahead of Blenheim so far in 2011. However, with the high August total, Blenheim has leapfrogged ahead of Whakatane, into second place behind Nelson.

Possible Sunshine

Most readers will probably be unaware of how the sunshine that Blenheim receives actually relates to the possible sunshine. “Possible sunshine” is the number of hours during the day when sunshine could be recorded, i.e. assuming no clouds in the sky to block the sun. The actual number of hours of sunshine received can be expressed as a percentage of the possible hours. The long-term annual average sunshine for Blenheim (1930-2010), is 2457 hours. The possible sunshine hours are 4256, i.e. on an annual basis Blenheim receives only 58 percent of possible sunshine hours. However, 235 hours sunshine for August 2011 was 75% of possible. Given that Blenheim is one of the sunniest locations in New Zealand, the figure of only 58 percent of possible sunshine received, indicates how New Zealand is aptly named the ‘Land of the long white cloud’. Being long narrow islands surrounded by ocean, New Zealand experiences a lot of cloud-cover. Other NZ locations and percentage of possible sunshine received are as follows: Auckland 50%, Palmerston North 42%, Wellington 48%, Nelson 57%, Christchurch 47%, Gore 39%, Greymouth 40%. Someone needs to remind Nelson that they are not supposed to receive as much sunshine as Blenheim. In contrast, the sunniest city in the world is Yuma, Arizona, USA, which receives approximately 4100 hours sunshine per annum, or 90% of 4555 possible hours.

Temperature

The Met Report one year ago detailed that 2010 recorded the fourth warmest (10.1°C) and 2009 the warmest (10.9°C) August on record for Blenheim, for the 79 years 1932-2010. Three of the warmest August mean temperatures on record for Blenheim occurred in the six years between 2005 and 2010. The mean temperature for August 2011 of 8.4°C is in complete contrast to those in 2009 and 2010. Table 2 indicates the markedly differing weekly temperatures during August 2011 and how they compare with August 2010. The second week of the month was 2°C below the long-term August average of 8.4°C, whereas the fourth week of the month was 3.8°C above the long-term average. In fact the average temperature of 12.2°C in the final week of August was also well above the September average (10.6°C), and not too far below the October average (12.7°C).

Table 2: August 2011 and 2010 weekly mean temperatures

Week 2011 2010 1-8 8.0 10.7 9-16 6.4 9.7 17-24 7.5 9.7 25-31 12.2 10.2

Mean 8.4 10.1

L.T.A 8.4 It is interesting to note that the average daily maximums for August 2011 and 2010 were both 14.6°C. However, the average daily minimum was 2.2°C in 2011 and 5.5°C in 2010. The average daily range in temperature of 12.4°C in August 2011, is the highest on record for the 26 year period 1986-2011.

Chill Hours

In all the Met Report articles that I have written I don’t think that I have ever summarised chill hours. This is mainly because grapes do not require a large amount of winter chilling and chill hours are not normally reported for viticulture. Some New Zealand horticultural magazines report winter chilling, especially with reference to the production of stone fruit, such as

apricots. Without enough winter chilling stone fruit do not flower and set fruit properly. There are a number of ways that winter chilling is recorded. The simplest is to sum the total hours below a threshold temperature. 7°C is often used as the base temperature below which chill hours are summed. The following text was accessed on 30 August 2011 from: cemadera.ucdavis. edu/newsletterfiles/Vine_Lines15654.pdf and it was written by UC Davis Viticulture Farm Advisor - Stephen J. Vasquez.

“As grape canes mature, their buds enter a type of dormancy in which their growth is suppressed despite otherwise favorable conditions.

Repeated exposure to cold temperatures dissipates this form of dormancy and once the chilling hour requirement is satisfied, it is only low temperatures which prevent bud burst. The number of chilling hours required by grapes varies among the different varieties, but most grapes only need about 150 chilling hours.

This is much less than that required by other temperate fruits such as cherries or peaches which may need up to 800 hours of chilling”. I had been told by a colleague Damian Martin that he had observed grapes in Northland a number of years ago that appeared to be suffering from a lack of winter chilling. They were exhibiting poor and irregular budburst and spindly growth. I had a look at the winter chilling from some of the Northland weather stations on the © HortPlus NZ Ltd web site. It appears that in some years they do not accumulate 150 chilling hours. Northland would appear to be the only region in New Zealand that sometimes does not accumulate enough winter chilling for grapes.

Table 3: Total winter chill hours below 7°C recorded in Blenheim, 2005-2011

June July August Total 2011 202 318 355 875

2010 219 346 149 714

2009 396 358 152 906

2008 270 307 257 834

2007 339 261 265 865

2006 397 234 266 897

2005 285 176 228 689

August 2011 accumulated significantly higher chilling hours than in recent years. However, the three month winter chilling total for 2011 is similar to a number of the previous years.

Frosts

Seventeen ground frosts for August 2011 was the highest August total since 1985, which recorded 19. Eight air frosts is the highest number since 2004, which recorded 10. This was quite a contrast with August 2010, when only five ground frosts and one air frost were recorded.

Soil Temperatures

When meteorological records were recorded manually, prior to the automation of weather stations, the thermometers and other instruments were read at 9am. Hence the reason that most automated weather stations still produce a 9am daily summary. The 9am soil temperatures are point in time readings at 9am, not an average over the previous 24 hours. Given that August 2011 recorded a higher than average number of ground frosts it is not surprising that the 10 and 30cm soil temperatures were both 1.2°C below average.

Growing degree days

The comparison between growing degree-days recorded in August 2010 and 2011 is rather interesting given that the mean temperatures were 10.1°C and 8.4°C respectively. You would naturally assume that the growing degree-days would be higher in 2010, with a higher mean temperature. This was not the case, with 2011 recording slightly higher degree-days. The very warm last week of August 2011, with an average temperature of 12.2°C, contributed nearly all the growing degree-days for the month. You need to remember that growing degree-days are only recorded above a base temperature of 10°C. In the latewinter-spring when the mean monthly temperature is often around 10°C, the growing-degree day totals, calculated on a monthly, daily or hourly basis can differ quite a lot, e.g. for August 2011 calculating the GDD’s from the mean monthly temperature of 8.4°C, the total is zero calculating the GDD’s on a daily basis from the daily max and min, the total is 18.1 calculating the GDD’s on an hourly basis from the hourly mean, the total is 38.9 As I have explained in a previous Met Report, when you are comparing growing degree-days you need to be aware of the method of calculation, especially when you are looking at data when the temperatures are around 10°C.

Rainfall

Rain was recorded on each of the six days from 11 to 16 August. However, these were the only days during August that recorded any rain. Blenheim’s rainfall total for the eight months January to August 2011 was 425 mm, or 95% of the long-term average of 446 mm.

Wind

Average daily wind-run for August 2011 was 218.1 km, only 89% of the long-term average. So far in 2011, only July has recorded higher than average wind-run.

Evapotranspiration

I mentioned in last month’s Met report that I would not normally comment on potential evapotranspiration (PET) in the winter as it is not particularly relevant in relation to plant water use. However, for the second month in a row PET has been a lot higher than normal. PET for August 2011 of 68.6 mm was 144% of average, or 21 mm above average. The last week of August with high temperatures was when the high PET was recorded. This PET is more applicable to the pastoral industry in August/September when dryland farms rely on a good flush of late winter / early spring pasture growth. Soil moisture in the top 35 cm at the Grovetown Park weather station fell by four percent in the last 10 days of August. An indicator of how rapidly soil moisture can fall once the temperatures start to warm up.

Rob Agnew Plant & Food Research

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