History of microclimate studies in New Zealand & Australia
Topoclimate Farm Planning is the only known programme identifying and mapping microclimates at a farm scale anywhere in the world.
Some preliminary microclimate studies were carried out at a farm scale in the Cromwell Gorge and Waitaki River valleys of Central Otago as part of studies into alternative areas for farming after hydro-electric dam construction.
The first regional microclimate study at a farm scale in the world was the Topoclimate South project. This study involved 4500 farmers and the survey of 820,000 hectares of land. The Project found a wide range of microclimates and encouraged the region to develop a whole range of new crops and pastures based on the information.
Why measure temperature?
Temperature is a primary value that needs to be determined when you are gathering climate data. Of all the measurable climate parameters, farmers should consider temperature second only to precipitation in terms of information value.
Changes to the way we Collect Temperature Data
Air Temperature used to have to be collected manually at a set time each day, usually 9am, and data collection by the manual reading of a temperature thermometer which was very labour intensive. The result was that no-one bothered to gather temperature data at the farm scale unless they had a very specific use for the information. What people tended to do was to rely on temperature data from long-term weather stations for their use. The trouble with this was that unless the Long Term Weather Station is located in exactly the same microclimate as your site there can be big distortions that can be generated by the data.
Let me illustrate this with a real case study. An agronomist in Southland, New Zealand was growing an experimental line of corn (Zea mays) in a trial plot on the Waimea Plains, 20 km east of Lumsden where there was a long-term weather Station (LTWS) with a good temperature record. On inspecting the crop in early February, he noted that the corn leaves had died and browned off prematurely before the corn cobs had developed. He suspected that there had been an out-of-season frost that had burnt off the leaves but needed to prove this to convince the seed manufacturers that this variety was not hardy enough to be grown in Southland. He checked the temperature record at the Lumsden LTWS and found that there wasn’t any record of a frost at that site on the suspected day in question, 22nd January 1999. So he began to doubt whether the browning off was caused by a rogue frost.
However, because there was a Topoclimate South temperature Datalogger adjacent to the site, he decided to check the data there as well. What he found was that the air temperature had in fact dropped below zero to -0.2 degrees C for a period of 35 minutes between 6.45 and 7.30pm that evening and this had been enough to cause the premature leaf death and browning off. This temperature was recorded at 1.2 metres above ground level, so at ground level it is predicted that the temperature would have been -2.2 degrees C. The trial site was clearly in a different cooler microclimate than the Lumsden LTWS and this clearly had implications for the varieties of crops that could be grown on that site.
How it has become feasible to measure microclimates.
It has only become feasible to measure microclimates on a larger scale since the invention of temperature dataloggers using microchips for temperature data storage in the mid 1990′s. Temperature dataloggers were originally invented to provide a timerelated record of temperature changes in cool storage containers for insurance purposes but some lateral thinking has seen them adapted for microclimate measurement in many rural environments in farming, forestry, horticulture and aquaculture. Automation of the temperature-gathering process has meant that it has become cost effective and efficient to collect intense temperature records from a site.An Air temperature record can be used for a whole raft of derived uses including;
Air Temperature is now seen as an excellent and simple primary factor to measure as it is a good surrogate for all sorts of other climate measurements. A temperature reading is the nett result of the cumulative effects of not only air temperature but also vegetation cover, aspect, slope, altitude, wind velocity and direction, level of solar radiation and level of cloud cover. The Air temperature is strongly influenced by all of these other parameters.
- Air temperature patterns including maximum, minimum and means for each dataset.
- Identification of temperature extremes, both hot and cold.
- Calculation of Accumulated heat for a site .
- Estimates of the frequency, maximum severity and duration of frosts.
- Calculation of Chilling Hours and chilling hour patterns for an area.
What has heat got to do with weather?
The amount of energy absorbed by the Earth from the Sun, and the amount of energy radiated into space by the Earth is, on average, perfectly balanced on an annual or yearly basis. However, because of their position on the Earth, some locations are warmer or cooler than others. This is the principal cause of weather.
As the gases in the Earth’s atmosphere heat up they begin to expand or spread out. As this happens, air begins to rush outward towards places where there is less pressure, towards those places where the air is cooler. This wind affects storminess, precipitation, and many other aspects of the Earth’s weather. Thus the unequal heating of the surface of the Earth is the principal cause of weather. There are a number of factors that cause this unequal heating of the Earth’s atmosphere.
Measurement of Accumulated Heat
All plants need heat to live, grow and set fruit and seed. Different plants have adapted to different levels of accumulated heat requirements from the mosses and lichens in Antarctica to the desert Mulga to the lush tropical rainforests. Each plant has a range of accumulated heat patterns that suits it best and usually dies if placed in a microclimate outside its required parameters.
Most plants have a trigger mechanism - a minimum amount of heat received on the leaf surfaces - before growth begins. The trigger mechanisms are different for different plants. Most Clovers, for instance, do not start to actively grow until air temperatures reach 10 degrees C for at least an hour. Consequently on cold days and in cold years there is very little clover growth in pastures in colder parts of Southland in New Zealand, in the very cool temperate climate of that region. Most temperate grasses on the other hand start to grow when the air temperature exceeds 4 degrees C.
Heat Measurement Units
Accumulated Heat is measured in units called Growing Degree Days, GDDs.
GDD = Average temperature for the day - Plant trigger point
To calculate the accumulated amount of heat on a sunny day, you use the trigger point for specific plants, usually 4 degrees C for temperate plants and 10 degrees C for warm temperate to tropical plants, and subtract that number from the average temperature for the day.
So if today’s temperature averaged 16ºC and you were calculating accumulated heat as units GDD10, you would have accumulated 6 degrees of heat for the day. Add these figures up for a growing season or year and you have a seasonal or annual GDD10 for your site.
It seems a crude and simplistic way of measuring heat but is surprisingly robust as a Heat measure. From an agricultural point of view, it has proved to be a very useful way of measuring and separating out microclimates of different parts of a farm. If a negative value is produced by the GDD calculation then this data is discarded because there is no net heat benefit from that recorded temperature. Negatives values are not recorded because the plant shuts down rather than losing heat.
If your weather station has only maximum and minimum daily temperatures, then you can still calculate GDD by using the following formula:
Annual GDD’s can be calculated by adding together the daily figures for all 365 days, 366 in a leap year. Computers have simplified these calculations enormously but if you have a software programme with a built-in GDD calculator, it would pay to read the instructions to check on which formula has been used and which base temperature.
The accumulated daily heat (GDD4) is shown graphically as being that area of the graph between the Green average daily temperature and the Green straight 4 degree C base temperature line also shown on the graph.
When you look at a map of New Zealand, it’s a long, thin country stretching from the subtropical north (Kaitaia 1452 GDD10) to the chilly cool temperate Invercargill in Southland with only 470 accumulated Growing Degree Day (GDD)s of Heat above 10ºC on average for a whole year (or less than 25% of Kataia’s accumulated heat). The whole of the South Island struggles to get over 1000 GDD10 whereas most North Island places exceed this figure. Judging by this table, you shouldn’t be able to grow grapes at Queenstown but you could (and they do!) at Christchurch, Blenheim or Nelson.
Chard Farm Winery was established on the north facing slopes of Kawarau Gorge in Central Otago after the site was identified using Topoclimate mapping of microclimates. Just down the road from Queenstown where it is too cold to grow grapes, in the Kawarau Gorge, farmers have discovered unique microclimates on the lower sloping fans and terraces above the engorged river, and grow world-beating Pinot Noir Wines in this area.
These developments show the importance of identifying microclimates. This data contained in the New Zealand map shown above is useful at a regional or country-wide scale, but is quite misleading if you try and extrapolate it to a farm scale. You actually need to take measurements of microclimates on your own farm and not rely on regional maps.
Another example is that of maize. Traditionally, Southland dairy farmers thought that they were too far south to grow a successful maize crop for winter feed for their dairy cows. After the Topoclimate microclimate survey was completed it was discovered that there were plenty of warmer, north facing, sheltered spots on many of their farms, where this crop received more than the minimum amount of accumulated heat and was very successful.
These examples show how identification of microclimates can add value to the farming systems in an area.
WHO CAN MEASURE MICROCLIMATES?
