An extended monsoon in India seen curtailing rains in Australia
18 October 2019
An extended south-western monsoon in India is causing a delay in the Australian monsoon season, according to the Australian Bureau of Meteorology – a phenomena brought about by the ongoing climate change.
The fundamental driver of all monsoon systems is the solar heating of the land during the Spring season (February-March in India) which helps establish a land-sea temperature difference.
According to a three-month forecast of the Australian weather bureau, the latest value of the Indian Ocean Dipole (IOD) (+2.15 °C) was the strongest weekly value since at least 2001, and possibly since 1997. The IOD is forecast to remain strongly positive until at least the end of spring.
This means below average rainfall for much of central and southern Australia during spring, and warmer than average temperatures for the southern two thirds of Australia. This is consistent with the current outlook.
IOD events typically have little influence on Australian climate from December to April, meaning its contribution to the drier outlook should start to reduce in early summer. This too is consistent with the outlooks beginning from December, which have fewer regions with drier conditions.
A weak negative phase of the Southern Annular Mode (SAM) is expected in the later part of October and into early November. A negative SAM in spring tends to bring drier conditions to parts of eastern Australia. It also increases the chance of spring heat waves occurring across southern and eastern Australia.
The bureau forecasts warmer than average sea surface temperatures off the northern parts of Western Australian coast are likely to contribute towards increased chances of above average rainfall for northern WA.
The El Niño–Southern Oscillation (ENSO) is expected to remain neutral until at least early 2020.
In addition to the natural drivers such as ENSO and the IOD, Australian climate patterns are being influenced by the long-term increasing trend in global air and ocean temperatures, it said.
Rainfall is likely to be below average across most of the country, excluding northern WA, for the remainder of October and November. The dry outlook for southern and northeastern Australia continues into December, according to the bureau.
Daytime temperatures are likely to be above average across Australia for the remainder of 2019 and into early 2020.
Nights are likely to be warmer than average for November in WA, the western NT, southern and western Queensland and eastern NSW. For December to February, nights are likely to be warmer than average nation-wide, it said.
The strong positive Indian Ocean Dipole (IOD) is likely to remain the dominant climate driver for Australia until early summer.
The impact of a delayed monsoon may have implications for Australian summer crops, with the planted area expected to fall 28 per cent in 2019–20 to around 758,000 hectares.
Summer crop production is forecast to fall by 20 per cent to 2.1 million tonnes, the Australian Agriculture Department said.