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Indian Ocean Dipole leaves legacy of locusts in eastern Africa

Ben Domensino, Wednesday February 19, 2020 - 13:59 AEDT


The strong positive Indian Ocean Dipole that drove parts of Australia deeper into drought towards the end of 2019 has caused a different problem in eastern Africa: locusts.


The Indian Ocean Dipole (IOD) is an index that measures the difference in sea surface temperatures on the eastern and western sides of the tropical Indian Ocean.


When the IOD is in a positive phase, more atmospheric moisture travels across the Indian Ocean towards Africa and drier air usually affects Australia.





Image: Mechanics and effects of a positive Indian Ocean Dipole.


In 2019, we saw one of the strongest positive IOD events on record. This resulted in a prolonged period of well below average rain over large areas of Australia, underpinning the nation's driest calendar year on record and exacerbating a multi-year drought.


On the other side of the Indian Ocean, eastern Africa experienced one of its wettest October-to-December periods (known as the 'short rains') in recent decades during 2019. Some places doubled their average falls for the season.


The rainfall anomalies caused by last year's positive IOD produced above-average vegetation growth in eastern Africa and below-average growth in parts of Australia. This contrast can be seen clearly in satellite images.





Image: Total vegetation cover anomaly in January 2020. Source: CSIRO


While many Australian farmers entered 2020 amid a crippling drought, some farmers in eastern Africa were hoping for one of their best cropping seasons in years. Unfortunately, these crops are being threatened by locusts.


The recent and continuing run of wet and relatively warm weather in eastern Africa has been a double-edged sword for African farmers, concurrently providing the ideal conditions for crops and locusts to flourish.


According to the United Nations Food and Agriculture Organisation (FAO), eastern Africa is now facing its worst outbreak of desert locusts in 25 years and the situation is expected to get worse in the coming months.




????Desert Locust update:

Press Release: Upcoming cropping season at risk across East Africa

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Eggs laid along migratory path expected to hatch in the coming weeks, giving ground to second round of invasion pic.twitter.com/4W5j8y4Hsz

— ICPAC (@icpac_igad) February 18, 2020



Africa's IGAD Climate Prediction and Application Centre (ICPAC) says that swarms of locusts have spread through eight countries in eastern Africa and have laid eggs along their migratory pathways. These eggs are expected to hatch between March and April, which is during the region's cropping season.


To make matters worse, the latest climate outlook for eastern Africa suggests that above average temperature and rainfall could continue over the next several months. According to ICPAC, this should provide ideal conditions for desert locusts to continue breeding and spreading during the coming months.


There are fears that the locust population could become several hundred times larger than it currently is over the next six months if effective control measures aren't adopted.


The unfolding desert locust invasion is likely to exacerbate food insecurity in an area that is already under pressure after years of unfavourable climatic conditions, conflict and poor macroeconomic conditions, according to ICPAC.


In Australia, a return of rain to parts of the nation's eastern states in the last two months has allowed some farming areas to produce their first crop in years. It's also caused some water storages to rebound after three years of gradual decline.


Unfortunately, the recent rain hasn't been heavy or widespread enough to break the drought and some areas have missed out.


While Australia isn't facing a horde of locusts in the coming months, the impacts of last year's positive IOD are still being felt in the landscape.


- Weatherzone

© Weatherzone 2020

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