Australian weather patterns are directly affected by a series of weather systems, often known as ‘climate drivers’. Weather systems shift atmospheric wind patterns and ocean temperatures, influencing both rainfall and temperature variability across the country.
The weather systems affecting Australia include:
• El Niño Southern Oscillation (ENSO)
• Sub-Tropical Ridge (STR)
• Madden-Julian Oscillation (MJO)
• Indian Ocean Dipole (IOD)
• Southern Annual Mode (SAM)
𝗪𝗵𝗮𝘁 𝘀𝘆𝘀𝘁𝗲𝗺𝘀 𝗮𝗳𝗳𝗲𝗰𝘁 𝘁𝗵𝗲 𝗥𝗶𝘃𝗲𝗿𝗶𝗻𝗮?
The SAM and STR weather systems affect the Riverina for a short period of time, not necessarily impacting drought conditions as compared to ENSO or IOD.
ENSO and IOD are generally attributed to long droughts or wetter years, affecting the Riverina for longer periods of time, from a few months to a few years.
𝗕𝗲𝘀𝘁 𝗼𝗳 𝗯𝗼𝘁𝗵 𝘄𝗼𝗿𝗹𝗱𝘀.
Australians praying for rainfall can monitor the IOD and ENSO weather systems. Bureau of Meteorology (BOM) reported the wettest year on record in 1974, when a negative IOD phase coincided with the La Niña phase of ENSO.
𝗪𝗵𝗮𝘁 𝗶𝘀 𝗜𝗢𝗗?
Indian Ocean Dipole (IOD), in simple terms, is a weather system affecting temperatures on the east and west Indian Ocean. Shifting temperatures directly affect evaporation rates, increasing or decreasing moisture in the atmosphere.
𝗛𝗼𝘄 𝗱𝗼𝗲𝘀 𝗶𝘁 𝗮𝗳𝗳𝗲𝗰𝘁 𝗿𝗮𝗶𝗻𝗳𝗮𝗹𝗹?
Moisture can be shifted toward or away from Australia on the positive or negative phase of the IOD, typically affecting winter and spring rainfall. When IOD enters a negative phase, east Indian Ocean temperatures increase. Coinciding strong winds (moving anti-clockwise) push moisture toward Australia providing significant rainfall to our region.
𝗪𝗵𝗮𝘁 𝗶𝘀 𝗘𝗡𝗦𝗢?
El Niño Southern Oscillation (ENSO) weather system affects temperatures on the central and eastern Pacific Ocean. ENSO also affects trade winds between the Americas and Asia. Australian droughts and wet seasons are directly influenced by ENSO entering the positive or negative phase. BOM and other weather forecast networks affectionately name the phases El Niño and La Niña.
El Niño is the positive phase of ENSO and can substantially reduce rainfall in Australia, being a key contributor to drought. When Pacific trade winds move anti-clockwise or weaken considerably, they push moisture toward the Americas. Consequently, Asian countries and Australia receive significantly reduced rainfall in the winter and spring months under a standard El Niño.
La Niña is the negative phase of ENSO and significantly increases rainfall in Australia; a saving grace for Australian farmers. Pacific trade winds move clockwise and become stronger, pushing moisture toward Asia. Under typical La Niña conditions, Australia and the Asian continent receive a higher amount of rainfall during winter and spring.
𝗪𝗵𝗮𝘁 𝗱𝗼 𝘄𝗲 𝗲𝘅𝗽𝗲𝗰𝘁 𝗳𝗼𝗿 𝘁𝗵𝗲 𝟮𝟬𝟮𝟬/𝟮𝟭 𝘀𝗲𝗮𝘀𝗼𝗻?
The Bureau of Meteorology constantly monitors both the IOD and ENSO weather systems using sea temperature, cloudiness, and trade wind strength as units of measure. As of June 9, 2020 IOD and ENSO weather systems remain neutral. However, both indicate a possible shift to negative phases before the end of 2020. The ENSO system is expected to reach the La Niña phase by early-to-mid spring (BOM, 2020).
𝗪𝗵𝗮𝘁 𝗱𝗼𝗲𝘀 𝘁𝗵𝗶𝘀 𝗺𝗲𝗮𝗻 𝗳𝗼𝗿 𝗳𝗮𝗿𝗺𝗲𝗿𝘀?
The La Niña weather system will increase the amount of rainfall received across Australia, hopefully marking the end of the current drought. It is still recommended that farmers continue conservative water use. The next La Niña phase might not be typical, but conditions indicate that broadacre farmers should remain positive and grape growers wary. The possibility of IOD entering a negative phase whilst lower typically affects Australia between May and December (BOM, 2020). Drought relief stemming from IOD will be short lived.
Drier conditions across the Riverina for the previous few seasons have encouraged growers to be more relaxed with their spraying program, creating higher disease risk. What can a relaxed program mean? Rainfall events occurring in early February during the 2019/20 season caused bunch rot infections across vineyards in the MIA. Growers not using a consistent spray program were caught off guard, and some suffered significant losses. Growers are advised to consider a thorough spray program for the 2020/21 season and budget for contingency sprays should disease occur.
𝗜𝗺𝗽𝗿𝗼𝘃𝗶𝗻𝗴 𝘄𝗮𝘁𝗲𝗿 𝘂𝘀𝗲.
Rain brought by La Niña, or the IOD weather system, can offer a short relief to drought but growers should consider beginning conservative water practices,
and improve soil water holding capacity.
Growers not maintaining a regular water schedule and/or monitoring farm soil moisture risk profit losses. Over-watering increases expenditure for no significant yield increase, and under-watering decreases expenditure but significantly decreases crop yield. Researching crop factors, soil type, and evaporation rates will assist growers to estimate crop water use and create a water schedule. However, using an accurate gauge to monitor soil moisture provides current data for growers to only water when and where necessary. Soil moisture gauges are not overly expensive, considering the benefit to farm profits. Growers should research the option best suited to the crop and soil types present on-farm.
𝗥𝗲𝗴𝘂𝗹𝗮𝘁𝗲𝗱 𝗱𝗲𝗳𝗶𝗰𝗶𝘁 𝗶𝗿𝗿𝗶𝗴𝗮𝘁𝗶𝗼𝗻.
Regulated deficit irrigation (RDI) can be practiced but requires the grower to accurately identify the crops physiological stage. Practicing RDI at falsely identified physiological stages can affect crop development and significantly reduce crop yield.
𝗦𝗼𝗶𝗹 𝘄𝗮𝘁𝗲𝗿 𝗵𝗼𝗹𝗱𝗶𝗻𝗴 𝗰𝗮𝗽𝗮𝗰𝗶𝘁𝘆.
Increasing the soil structure and organic matter (OM) are central to improving the water holding capacity of the soil. Soils containing higher OM hold water for longer. Organic matter also prevents water losses in sandy soil types and improves the soil structure to prevent waterlogging in clay soil types. Broadacre farmers are best to use minimum tillage systems and incorporate crop stubble to increase OM. Horticultural crops can use compost manures or grape marc. Unstable soil structures can collapse, decreasing both soil pore size, and pore distribution. No pores translate to no drainage and limited water runoff, which can result in waterlogged crops. Growers are encouraged to consult their local agronomist on how to improve poor soil structure.
𝗗𝗲𝗰𝗿𝗲𝗮𝘀𝗶𝗻𝗴 𝗲𝘃𝗮𝗽𝗼𝗿𝗮𝘁𝗶𝗼𝗻 𝗿𝗮𝘁𝗲𝘀.
Higher temperatures increase evaporation on-farm, increasing water use. Growers should consider sowing a cover crop or spreading mulch to decrease orchard/vineyard temperatures.
Most of the information used in this factsheet has been sourced from the Bureau of Meteorology (BOM). For more information and for monitoring the IOD and ENSO weather systems, visit the Bureau of Meteorology’s website at www.bom.gov.au