What are they?

Scientific name: Schistocerca gregaria

Desert locusts are known to be solitary, however, they swarm when there are heavy rains in an arid region. This is because they have access to food as well as conditions that favour their breeding and maturation. A swarm can be made up of billions of locusts and can be as large as cities. For example, in Kenya, a swarm was estimated to be 60km long and 40km wide, which made it roughly four times the size of Nairobi.

In this swarm phase, they are known to eat their own body weight (two grams) in food each day. This makes them highly destructive to crops as they consume their leaves during their migration from one place to another.

What brought on this outbreak?

In May 2018, a powerful cyclone, known as, Mekunu, hit the Arabian Peninsula causing heavy rainfall that created desert lakes in Saudi Arabia. This created an ideal environment of warm, sandy and wet soil, for desert locust eggs to hatch, develop and breed. A period of dry conditions would normally result in the death of these locusts, however, another tropical cyclone, Luban, hit the area in October 2018. This provided a lifeline for the continuation of the first outbreak and enabled the successful breeding of three desert locust generations.

It is this outbreak that spread to Yemen, where due to political instability and an incoherent government response, the outbreak continued uncontrolled. In 2019, winds from another tropical cyclone, Pawan, facilitated the migration of these desert locusts to East Africa. Political instability and limited capacity contributed to the lack of response and made this outbreak, not only the worst in 25 years for Ethiopia and Somalia, but also the worst in 70 years for Kenya.

What is their relationship with climate change?

This outbreak was brought on by the increase in tropical cyclones reaching landfalls all linked to the Indian Ocean Dipole (IOD). The IOD is a climate system that affects the weather in East Africa & the Arab Peninsula, and Indonesia, New Guinea & Australia. The IOD has three phases – positive, negative and neutral. It is the positive phase that is linked to the desert locust outbreak.

In the positive phase, the winds blow east and the waters around East Africa & the Arab Peninsula warm up resulting in cyclones and heavy rainfall in the region. The frequency of cyclones increases during the positive phase due to an increase in warmth and moisture which acts as fuel to these storms.

The IOD was in positive phase in 2018 and 2019 from June to December. However, in 2019, the IOD was at an extreme positive level. This led to not only an increase in rains in East Africa, but also an increase in bushfires in Australia. This is because as it rains in East Africa, Australia develops drought-like conditions.

Research has shown that there has been an increase in positive phases in the IOD over the years. This is linked to human-induced warming of the western Indian Ocean (Africa) in comparison to the eastern Indian Ocean (Australia). This results in heavy rainfall, cyclones and bushfires.

A study conducted in 2009, found that there has been an increase in the frequency of positive IOD phases since the 20^th century. According to the study, at the beginning of the 20^th century, a positive IOD phase was estimated to occur around 4 times in a 30-year period. However, between 1989-2009 (30-year period), 10 positive IOD phases occurred.

It is estimated that further climate change would only increase the frequency of positive IOD phases by a factor of three by 2099. This will increase the number of locust outbreaks in the Horn of Africa as more cyclones occur feeding into the lifeline of the desert locusts.

CHRIS HANI