8 minute read
Can climate info help with risk management?
Grain farming is risky business. Growers invest in crops that may be lost to drought, frost, heat, disease or untimely rain at harvest. Not only is production risky, but growers face price risk, cost risk, finance risk, especially with higher interest rates, and risks to their own safety and the safety of staff.
In recent consultations that GRDC held with grain growers and advisers, the increased riskiness of grain farming is one of the issues that has been raised. In response, the GRDC developed the National Risk Management Initiative which is now called RiskWi$e. This project is led by CSIRO(Rick Llewellyn based in Adelaide and Lindsay Bell based in Toowoomba).
The definition for risk used in RiskWi$e is “uncertainty of outcomes that matter”; a definition that applies to the rainfall and frostiness of the coming season. Any reliable information that reduces this uncertainty is potentially of value to grain growers.
This article addresses how climate drivers such as El Nino and La Nina and the Indian Ocean Dipole influence rainfall, heat and frost over the growing season. A close to perfect forecast that reduced the uncertainty would make decisions easy and substantially reduce the risk Seasonal forecasts are far from perfect, and we will always have a shift in probabilities.
It is frustrating when the outlook is close to 50% chance wetter than average and 50% chance of being drier. What this means is that we need to use the long-term records for planning and assume that each decile is equally likely.
Where to find information on climate drivers
Most grain growers and advisers are aware of climate drivers such as El Nino, La Nina and the Indian Ocean Dipole. For a refresher, it is worth visiting the excellent material from the Bureau of Meteorology and the award winning videos on the climate dogs developed by Agriculture Victoria and a general description of climate and weather forecasting.
The ABC has an explainer about what’s been driving Australia’s climate recently . The Bureau of Meteorology encourages users to use forecasts from their climate model rather than paying too much attention to climate drivers.
This is a reasonable request as the climate model takes into account a vast amount of information from the oceans and atmosphere when generating the forecast. However, many grain growers and advisers find it helpful to follow the climate drivers for interest but also understanding and confidence in the forecast.
What is the influence of climate drivers on growing season rainfall in the southern grains industry?
The Local Climate Tool was designed to examine the impact of ENSO and IOD on southern Australian rainfall Local Climate Tool (forecasts4profit.com.au) . The screen grabs (Figure 1) show the change in odds for growing season rainfall at Mildura. With no forecast and just randomly sampling the historical record, there is a 33% chance of drier than 136mm (red slice), a 33% chance of wetter than 207mm (blue slice) and 33% chance of the rainfall being between 136 and 207mm. In the 28 El Nino years since 1900 the chance of being in the driest third increases to over 50% and the chance and in a La Nina the chance of being in the wettest third increases to 48%. In Mildura, like much of the southern grains region, the swing in the odds of growing season rainfall are even greater for the two phases of the Indian Ocean Dipole
These pie charts show that there is a swing in probabilities, but even the strongest swing of a negative IOD only shifts the chance of less than 136mm from 33% (1 in 3) to about 20% (1 in 5). This shows that it would be a mistake to assume that a negative IOD eliminates the chance of a dry season.
The Local Climate Tool can be used for a range of locations as shown in the maps in Figure 2. The important message from Figure 2 is that the swings in probabilities across the region are broadly the same. When we developed this tool as a part of a consortium of SARDI Climate Applications, Federation University and Agriculture Victoria in an earlier GRDC project, we were quite surprised at how consistent the swing in probabilities was across the region.
What is the influence on temperature compared to rainfall?
Table 1 shows the difference in April to October rainfall, minimum and maximum temperature and frost sum and heat sum for a range of towns in the SA and Victorian Mallee. El Nino and positive IOD are drier, with colder minimum temperature and warmer maximum temperature and a higher accumulated frost sum and heat sum. The most likely reason is that El Nino and positive IOD years have less cloud cover hence colder nights and warmer days.
The shifts in rainfall are greater than the shifts in temperature. A grain grower is not so much concerned with the number of cold nights, but the chance of the late frosts. Figure 3 that shows the date of the last night in each year since 1957 that the temperature was equal to or below zero degrees Celsius. Although the latest year (2002) was an El Nino year, of the other six years in the 10% latest cold night, two were El Nino, one La Nina and three neutral years
Screen grabs from Local Climate Tool (forecasts4profit.com.au)
Table 1 Above; Climate indices averaged over all years (1957-2023), along with the difference from the average during years with specific climate drivers of El Nino (EN), La Nina (LN), Indian Ocean Dipole positive (IOD +) and negative (IOD -). Climate indices include Apr-Oct Minimum Temperature, Maximum Temperature and Rainfall, plus Cold Sum and Heat Sum accumulated between 1-Aug and 31-Oct. Values less than the average are shaded.
The date of chance of a late cold night that might lead to frost damage will only ever be predicted by short term weather forecasts. The Frost Potential maps show forecast low temperature thresholds for various locations across Australian weather station locations. While climate drivers provide a shift in the odds for rainfall cold nights, they are less reliable for cold nights. Furthermore a grain grower is likely to require a major shift in the probabilities to change frost related decisions
An uncertain outlook for 2024
Updates on climate drivers are available from the BoM (updated twice a month) Climate Driver Update (bom.gov.au) and for Victoria by Dale Grey with The Break. The BoM have a YouTube channel and the May Grains Climate Outlook - SA, VIC & Tas can be accessed here.
As a summary, the El Nino that developed late in 2023 has dissipated with interesting possible developments in both the Indian and Pacific Ocean In the Pacific Ocean, some international models are predicting the development of a La Nina later this year. Although this has received press coverage, it is still early to make the prediction.
It is important to note that other international models are favouring neutral conditions but none are pointing to El Nino. Recent values of the Indian Ocean Dipole (IOD) are above the positive IOD threshold (+0.40 °C). If a positive IOD develops, it would be earlier in the calendar year than is typical historically.
The early development of a positive IOD is not the only surprise, it is unusual (but not unprecedented) for there to be a positive IOD (associated with dryer springs in Australia and a La Nina (associated with wetter springs). It is more common for a positive IOD to be associated with El Nino and a negative IOD to be associated with La Nina.
Graeme Anderson (Vic DPI) has the useful football analogy for climate drivers. Early in the season there is a lot of talk about how different teams will go but by July and August we have a lot more information.
Climate scientists urge caution about over interpreting talks of climate drivers this early in the season, so it is more a case of what to look out for. The current forecast from the Bureau of Meteorology is increased chance of dry for the month of May but returning to a neutral to wetter odds later in the season.
Join our Better Frost Decisions Facebook Group!
A public group providing frost updates and frost response information, including;
Support to identify frost damage
Info to assess your options for frosted crops
Planning for next season
An opportunity to reflect and review on frost events and your response.
Join Here: https://www.facebook.com/groups/ 1120487535225571
