Climate indicators and how to use them
Author: Rebecca Barr | Date: 27 Jun 2015
The BoM's manager of Climate Prediction services Dr Andrew Watkins, says our weather is affected by a number of different climate drivers, of which the El Niño Southern Oscillation (ENSO) is one of the most influential.
“ENSO is the response of the climate to movements of warm water in the Pacific Ocean. El Nino is when the warm waters move towards the eastern Pacific, the clouds move east, taking rains towards the Americas and away from Australia. The opposite, when the warm water comes west and brings clouds and rain this way, is La Niña,” he said.
El Niño events usually last for one season, developing in autumn and winter and starting to dissipate by summer, though have been known to last between six months and two years. El Niño occurs every three to five years on average.
“In a ten-year period, we would expect to see about two El Niño years, two La Niña years, and six neutral. While La Niña can often follow two years in a row, it’s uncommon for El Niño to do so; it’s usually a one-year situation, affecting winter and spring rainfall and temperature,” he said.
The Indian Ocean Dipole (IOD) is a similar phenomenon to ENSO, only in the Indian Ocean. It is currently neutral, but about half the models surveyed by the BoM suggest it could move into a positive mode in spring. A positive IOD is generally associated with lower rainfall in south-east Australia.
Since 1958 there have been 11 years where the IOD is positive, with the average rainfall in these years in the South Australian wheat belt at decile 3. While the relationship between ENSO and IOD is complex, about half of all IOD events occur in El Niño years, such as this year.
“The effect of a positive IOD is similar to El Niño, though it is shorter lived as it usually starts in winter and collapses in late spring-early summer, when the monsoon season starts. The combination of El Niño and a positive IOD are likely to result in particularly dry conditions for early spring,” Dr Watkins said.
The easiest way for a grower to keep ‘on-top’ of these climate influences is by following the Bureau's ENSO Wrap Up, released every second Tuesday, and by keeping an eye on outlooks from POAMA, the Bureau of Meteorology's climate outlook model.
“Unlike older statistical forecasts, POAMA uses mathematical equations representing the laws of physics to model the ocean and the atmosphere. It can effectively take into account the complex relationships between each of these indicators to provide the more probabilistic outcomes,” Dr Watkins said.
Once a grower has the best available climate information, decisions can then be considered to make the most of the forecast conditions.
It is essential to always keep in mind that weather forecasts can only ever be probabilities; there will always be a level of risk involved with making agricultural decisions based on climate outlooks.
Diversifying a cropping program with a range of crops, varieties and sowing dates, is a solid strategy for minimising risk exposure.
At this stage in the season, the key decision growers need to make is to choose whether to apply or hold off on nitrogen applications. The GRDC-funded app ‘CliMate’ can help make this decision by analysing seasonal and agricultural factors.
Dr Andrew Watkins, 03 9669 4360, firstname.lastname@example.org
- Know your environment to get the most out of N
- Read more about POAMA
- Climate Kelpie
- BOM ENSO Wrap-Up
- CliMate: http://www.australianclimate.net.au/
- DEPI Climate Risk, The Break and Climate Dogs
- Bureau of Meteorology Climate Outlooks
- Very Fast Break YouTube Channel
GRDC Project Code CMA00003