Meteorologists are warning of a significant El Niño event developing in the coming spring and summer, which could bring the most severe drought conditions in years. Philip Lee of CompleteLee Nuts Consulting explains what macadamia growers can do now to prepare.
By Philip Lee, CompleteLee Nuts Consulting
From all reports recently meteorologists are warning of the most significant El Nino event developing in the coming Spring and Summer 2026, likely to continue through 2027 and 2028.
El Nino is a natural climatic pattern featuring warmer than average temperatures in the central and eastern equatorial Pacific. It disrupts global weather and rainfall, triggers droughts in regions like Southern Africa and elevates global temperatures. This short article highlights the impact of previous “dry cycles” on macadamia production in South Africa, illustrating the correlation between annual rainfall and macadamia yields, emphasizing the negative effect of moisture stress on nut yields at selected important stages of the seasonal phenological cycle and provides some suggestions on what growers can do to mitigate the negative impacts.
High temperatures aggravate the impact of lower rainfall.
During previous dry cycles precipitated by El Nino events, it was common to experience extremely high temperatures in the Spring and early summer months August through to November, coinciding with flowering, fruit set and immature nut drop. In the absence of any meaningful rain over this period, temperatures more than 33°C can be recorded on 10 to 15 days in each month during dry cycles. The macadamia flower is the most delicate organ in the tree and therefore the most sensitive to heat stress, becoming desiccated in the hot, dry air, resulting in very poor nut set. No amount of irrigation can prevent this negative impact on nut set, as the macadamia tree shuts down the water flow by closing stomata in such hot and dry conditions.
Rainfall and nut yield
Some data from a farm in the Kiepersol area show the relationship between rainfall and yield, despite the fact that all the trees were fully irrigated over the period under study.
Illustrated in Figures 1 and 2, the exceptionally high rainfall on this farm is overlayed with total nut production and nut yields per hectare from 2009 to 2020. There are very few macadamia farms in Southern Africa that can boast long term average rainfall of 1 352mm per annum, certainly an important key to the high productivity of this enterprise. The very strong correlation between annual rainfall and nut production is clear to see. In the wet cycle from 2009 to 2014, with average rainfall at 1 519 mm, average yield of 4,5 tons DIS/ha was achieved (average total production 196 tons DIS), while in the “dry cycle” from 2015 to 2020 with average rainfall only 1 143 mm, average yield was still an impressive 3 tons DIS/ha (average total production 131 tons DIS), but still 33% lower than average yield during the preceding wet cycle.
It is notable to point out the lag in production behind the rainfall data. So, the high rainfall in 2014 translated into the highest crop in 2015, while the lowest rainfall in the 12 years in 2015 translated into the lowest yield in 2016.
Referring to the trail blazing work of Stephenson et al. (2003), Figure 3 illustrates the yield depression resulting from mild stress applied at various times of the season. As Dr. Stephenson said at the first International Macadamia Symposium in Nelspruit in 1999, “The first priority for irrigation should be to avoid stress from early nut growth through to maturity, particularly the oil accumulation stage when both yield and kernel quality are most sensitive.” As Figure 3 shows, stress at the time of premature nut drop in November has the greatest impact on yield, with accumulated yield from age 8 to 12 of trees stressed at this stage being roughly half of the yield from unstressed trees.
There is also a significant depression in yield from trees stressed during flower development in July/August, as well as trees stressed at the start of nut maturation in December. In most seasons during this study it was also observed that stress imposed at nut maturation had the largest negative impact on kernel recovery percentage, reducing TKR to 21.5% from trees stressed at nut maturation compared to the 32% TKR of the unstressed treatments in the worst case which occurred at tree age 9.
The least amount of yield was lost when trees were stressed at flower initiation. The clear message from this work is that macadamia trees need to be well watered from the emergence of flower buds in July/August through until the end of March, to avoid any stress at the critical times in order to derive the full benefit of irrigation. So if water is in short supply, then the months in which it is not critical to irrigate are the cooler months of April to July. Whatever water has been accumulated in storage dams during the rainy season to the end of March, can then be saved by not irrigating, or using water as sparingly as possible from April to July so that it can be used thereafter, especially in the most critical months of September to November.
Preserving soil moisture
The use of mulch to preserve soil moisture cannot be over stressed. Figure 4 clearly shows the impact of ground cover on soil temperature, 43,8°C in bare soil, 24,5°C under cut grass and 19,5°C under growing vegetation. Bare earth in the line of macadamia trees should be avoided at all costs, especially in drought conditions and especially in young orchards age 0 to about 7, before canopy growth provides shading over tree drip area. Macadamia tree feeder roots just under the soil surface will be burnt to death at 43,8°C if the bare earth surrounding the tree is not covered by an appropriate mulch of cut dried thatching grass or cane tops or a living mulch like Arachis pintoi (wild peanut), as illustrated in Figures 5 and 6.
