Perfect recipe for an invasion of locusts

In August 2019, the East African Crop Surveillance Network expressed concern over the increasing risk of locust invasions in Sudan and Ethiopia. Already in December, the first alerts of massive proliferation of the insect were disseminated. This type of locust feeds on all the vegetation it finds without having a preference for one crop or another. For this region of the world, already battered by successive famines, this is very bad news.

Weather factors have all joined forces

The growth, development, proliferation and survival of this type of locust depends on very precise weather conditions. Since it is difficult to bring all these conditions together at the same place, the invasion of the Horn of Africa is unprecedented. This region of the world, however, is no stranger to destructive invasions of insects or diseases. By the early 1990s, 50% of robusta coffee trees had been decimated by the disease. In early 2000, 60% of bananas were eradicated by a bacterium and since the mid-2000s, cassava and corn crops have suffered the same fate.

Each stage of the life of a desert locust is governed by weather conditions. The laying of eggs, their hatching, the development of the insect, the hardening of their wings, the stage of maturity and the speed of movement of adults need precise weather conditions. Its evolution is influenced by the amount of rain, the humidity contained in the soil, the temperature of the soil and the air as well as by the surface winds. All play a role in the spread and intensity of the invasion.

The Indian Ocean dipole

Between June and December 2019, the Indian Ocean saw its surface waters off the coast of Africa warm. This mechanism is called the Indian Ocean dipole. When surface waters warm up on the eastern portion of the Indian Ocean, the dipole is said to be in the negative phase. If the water heats up near the coast of Africa, then it is in a positive phase. A dipole in the positive phase of the Indian Ocean promotes the formation of clouds over the eastern portion of Africa. It is during this period that the rains will be more abundant over this region of the globe.

Normally between October and December, the Horn of Africa experiences its shortest rainy season. Except that in 2019, the northwest Indian Ocean experienced its highest number of tropical cyclones for this time of year. The combined effects of the rainy season, intensified by the Indian Ocean dipole, and tropical activity, resulted in above normal amounts of rain over East Africa and the Middle East. This abundance of rain encouraged the exponential growth of plants, and since this type of locust feeds on all plant species, its pantry was full. This prolonged period of rain, where the climate is normally semi-arid, allowed the locusts to increase their reproductive cycle. Furthermore,

The invasion affects many populations

The first hordes migrated from Yemen and Djibouti and then invaded several other countries. Today, they are found in Ethiopia, Eritrea, Sudan and South Sudan, Kenya, Tanzania and Uganda. Severely affected by drought and famine for decades, crops in this region are now threatened by the Desert Locust. The food security of these populations is highly at risk.

In the context of climate change, the melting of the Arctic is affecting the intensity of the trade winds in the tropics. Stronger trade winds could mean a more frequent recurrence of the Indian Ocean dipole. This would again provide more favorable conditions for locust invasions in a region of the world that is in dire need of respite.

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