Johannesburg - Heavy rain leads to growth of vegetation in arid areas, providing locusts with the conditions needed to develop and reproduce, according to the World Meteorological Organisation (WMO).
This comes after the locust outbreak in East Africa that has an ‘unprecedented threat’ to food security and livelihoods, in a region that is already vulnerable to the impacts of climate change.
The widespread rains came in a year of extremes in East Africa - 2019 started with a drought, putting more than 45 million people at risk from food insecurity, and ended with abnormally wet conditions.
Climate scientists have warned that such conditions risk becoming increasingly common if emissions continue to rise.
The WMO said an unusual cyclone season in East Africa in 2019 is linked to an ocean circulation pattern known as the Indian Ocean Dipole (IOD), which measures the difference in water temperature between opposite sides of the Indian Ocean.
The IOD is a primary driver of climate conditions stretching from Africa to Australia.
The positive phase of the IOD in 2019 was the strongest for six decades. These conditions led to severe rainfall and flooding in East Africa, as well as contributing to the unusually dry conditions in Australia that drove the current bushfires.
WMO said that the positive phases of the IOD were becoming more common, and scientists believe climate change was responsible. Academic studies have found that strongly positive phases of the IOD have happened more often in recent decades, and that climate change is behind the increase.
As greenhouse gases continue to heat the ocean and the atmosphere, extreme events caused by the IOD are predicted to become increasingly common. Unusually positive IOD events could happen nearly three times more often this century if emissions continue to rise, according to a 2014 study.
A separate study also found they would be twice as likely to happen even with only 1.5°C of warming - little more than has already been seen.
According to Food Agriculture Organization (FAO). Increased extremely positive IOD years would likely bring flooding and cyclones like those seen in 2019 to already vulnerable and food insecure regions. Wet conditions could also lead to worse locust outbreaks - in a worst-case scenario they could damage the livelihoods of one tenth of the world's population.
"The West Indian Ocean, including the Arabian Sea, was warmer than usual during the last two seasons. This is largely due to a phenomenon called Indian Ocean Dipole (IOD), and also due to the rising ocean temperatures associated with global warming," Senior Scientist, Indian Institute of Tropical Meteorology Dr Roxy Mathew Koll said.
Koll said that heavy, prolonged rains over the west coast of India (including Rajasthan) during the latter half of the monsoon— and unusually strong cyclones during the post-monsoon season— may have links with these warm ocean temperatures in the west Indian Ocean region.
“Cyclones draw their energy from the ocean and hence such an environment is quite favorable for an increased number of cyclones. Another weather phenomenon called the Madden Julian Oscillation (MJO)— a band of eastward moving convective clouds— was also quite active in the Indian Ocean when the IOD was at its peak," said Koll.
He said MJO provides conducive atmospheric conditions for cyclogenesis, while the IOD provides favorable oceanic conditions—hence the recipe has been right for a stormy west Indian Ocean.
"Besides, our recent research shows that the rapid warming in the Arabian Sea has resulted in a threefold rise in widespread extreme rains, leading to largescale floods, along the west coast and parts of central India.”
Senior Locust Forecasting officer, Food and Agriculture Organisation (FAO) Keith Cressman said as Desert Locust were fully integrated with nature, weather and environmental conditions have dramatic impacts on locust numbers and migration.
"Historically, heavy rains associated with cyclones that form in the Indian Ocean and make landfall in the Arabian Peninsula and the Horn of Africa have led to Desert Locust plagues."
“In the past few years, there has been a significant increase in the frequency of such cyclones at the beginning and end of the summer period. For example, there were 8 cyclones in 2019 when in most years there are only one or two."
Cressman said that three cyclones in 2018 and two in 2019 have contributed to the current Desert Locust upsurge in the Horn of Africa where large and numerous swarms are present in Ethiopia, Somalia and Kenya.
"If this trend continues, whether it is specifically attributed to climate change or not, is likely to lead to more Desert Locust outbreaks and upsurges in the Horn of Africa," Cressman said.
Professor Axel Hochkrich, Trier University added that climate change may well play a role here, mainly because, according to forecasts by international climate researchers, precipitation will increase in the southern Arabian Peninsula and northern East Africa.
"This means that there will be more frequent very humid phases, such as we have had since 2018, and it is therefore possible that such swarms will simply occur more frequently.”