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Mainstream, VOL LVIII No 26, New Delhi, June 13, 2020

Locusts: The piranhas of the skies | Amit Schandillia

Saturday 13 June 2020


by Amit Schandillia

How the wildfires in Australia, the floods in Oman and the locusts in Vidarbha are linked

If the coronavirus pandemic was not crippling enough, India is now reeling with the worst locust plague in decades. The crop-damaging migratory pests have swarmed Rajasthan, Gujarat, Punjab and Madhya Pradesh, and breached the eastern part of Maharashtra, the Vidarbha region, which is also at the heart of rural distress in the state. But to understand where these parasitical tropical grasshoppers have flown in from, in such large numbers, it’s important to take a deep dive into the role the Indian Ocean plays.

Almost every weather and ecological event across South Asia and Australia is directly or indirectly impacted by the Indian Ocean, which is the warmest of all five oceans as it is landlocked on three sides, insulating it from the icy Arctic waters. It’s only a narrow corridor between the Indonesian archipelago and Australia to its east, which connects it with a slightly cooler Pacific.

All weather experiences witnessed in the region, from Africa to India to Australia, boil down to one piece of thermodynamics: The Indian Ocean Dipole. As the name suggests, this dipole is the temperature difference between the two sides of the Indian Ocean — the east that meets Africa and the west that meets Australia. If it’s warmer near Africa, it’s a positive dipole; if it’s warmer near Australia, it’s a negative dipole. Warmer waters, we must note, trigger low pressure, resulting in rains in the area; cooler waters lead to the opposite effect.

Each year, with the onset of summer, some Arctic ice melts and runs into the Pacific and, aided by the South Easterlies, pushes the cooler Pacific water through the narrow corridor into the Indian Ocean. This, in turn, pushes the warm Indian Ocean water further westward as cooler water accumulates in the east. Since warm water leads to rains, this results in thunderstorms and rain conditions around Africa and the Middle East, while Australia faces drought-like conditions.

Remember the devastating bushfires that killed more than 400 Australians and countless animals last year? Yes, it had something to do with this phenomenon. The stronger the positive dipole value, the drier the air above areas like Australia. Dry air and heat conditions lead to such catastrophic fires.

Now, typically, the temperature difference is within a degree. But two years ago, it shot past two degrees. In meteorological terms, that’s massive. The dipole was so strong that parts of the Middle East and coastal Africa experienced unprecedented rains and flooding. One such flood led to the formation of ephemeral lakes in the middle of the desert in Oman.

Something happened in those lakes.

Millions of locust eggs, which were lying dormant for close to 20 years, awaiting favourable weather conditions, began to hatch. This went undetected simply because, er, who ventures that deep into the desert?

Now desert locusts are no ordinary crop-ravaging pests. These piranhas of the sky can chow down their own body weight in food in a day. That’s about two grams. It might not sound much, until you realise there are possibly as many of them in a single swarm as there are people in Bangladesh. They can also fly up to 150 km a day, riding the wind.

A mother locust lays 50-100 eggs in a single drop. That happens once every three months. So, even by the most conservative estimate, we’re looking at a swarm inflation of 20 to 40 times every quarter. Once hatched, they hop out in the direction of sprouting grass. Eventually, they grow wings and take flight. From this point on, it’s a feeding frenzy until death. Such is their appetite that locusts end up devouring each other when they run out of vegetation.

Exhaustion is fatal for it because any locust stopping to rest is quickly consumed by its friends. So why not fly solo to be safer? Well, you never know when you might need to eat your mates.

A single swarm can easily devour up to 200 tons of food in a single day. You can kill a few, but how do you control a number like this? The hoppers that hatched in Oman, in 2018, rode the Westerlies, unleashing their fury on vast tracts of Africa, to reach India this year, through Iran and Pakistan. This superswarm is the biggest we’ve seen in 27 years, and approximately the size of five Mumbais in terms of population density. For reference, one such swarm in 1875 in the US was the equivalent of the populations of Maharashtra and Kerala put together. What makes this locust attack even worse is that it comes in the midst of the global lockdown to curb the spread of coronavirus, which has stalled all efforts to control the infestation through pesticides and other measures.

If all this sounds apocalyptic, recall what helped them hatch in the first place. Torrential rain, where it shouldn’t have occurred. What triggered that? The abnormally high dipole. And why was that? The ice caps melting. This most certainly was an aberration. But should the trend of global warming continue, it may not be so uncommon anymore.

Amit Schandillia is a freelance writer and history enthusiast

(Courtesy: Mumbai Mirror, May 31, 2020 )

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