The Link Between Australia’s Wildfires and Kenya’s Floods, Locust Invasion
Many parts of Kenya experienced torrential rainfall for the last couple of months resulting in floods, landslides and loads of dry memes, ironically. Currently, the country is experiencing chilly temperatures, an unusual occurrence this time of the year. And now the deluge has led to locust plagues of biblical proportions, make it the worst locust swarm in decades, as the insects are able to consume enough food for millions of people in a single day.
This uncommon weather can be attributed to the Indian Ocean Dipole. This is the difference in sea surface temperatures between the eastern and western tropical Indian Ocean.
Here in Kenya, when warmer sea surface temperatures are experienced, heavy rainfall occurs, while hot dry conditions (conducive for wildfires) are experienced in Australia. When warmer sea surface temperatures are experienced off the West Coast of Australia, Australia is likely to experience heavy rainfall, while Kenya experiences drought conditions.
The larger the difference in temperatures between the eastern and western tropical Indian Ocean, the more severe the climatic effects will be.
Sea surface temperatures are measured just off the coasts of Kenya and western Australia. In some years, temperatures will be warmer in the western half of the Indian Ocean and in other years they will be warmer in the eastern half. This dipole cycles between these extremes over three to five-year periods, ordinarily with a 1°C difference in sea surface temperature. Between these extremes, temperatures will be fairly uniform across the tropical Indian Ocean.
The 2019 to 2020 dipole was unusually strong, the strongest in recorded history, with a temperature differential of 2°C. This is more than double the intensity of the average event.
As a result, there were very strong low-pressure systems over parts of the western Indian Ocean, such as Kenya, inducing heavy and prolonged rainfall. This, in turn, favours the rise of desert locusts, which, despite their name, thrive following periods of heavy rainfall that trigger blooms of vegetation across their normally arid habitats in Africa and the Middle East. A prolonged bout of exceptionally wet weather, including several rare cyclones that struck eastern Africa and the Arabian Peninsula over the last 18 months, is the primary culprit. The recent storminess, as stated, is also related to the Indian Ocean Dipole.
The precise effects of these ramifications were predicted way before the onset of the sea surface temperature gradient, but as the placard adage goes, every disaster movie starts with the government ignoring a scientist.
The worst of the locusts’ outbreak may be yet to come. The rains tipped the situation into something not only very usual but very dangerous by effectively enabling at least another two generations of locust breeding. By June this year, the desert locusts will have increased their numbers 400-fold compared with today, triggering widespread devastation to crops and pastures in a region that’s already extremely vulnerable to famine. Over 13 million people in Djibouti, Eritrea, Ethiopia, Kenya, and Somalia experience severe acute food insecurity, while another 20 million are on the brink. It’s all about timing. Most crops are planted at the beginning of East Africa’s first rainy season, in March or April. When that rainy season starts and farmers are ready to plant, that will coincide with this new generation of swarms. A confluence of unusual weather and climate conditions have helped stoke the outbreak.
The Indian Ocean Dipole is caused by changes in trade wind strength which can make the ocean cooler.
When trade winds blow, they push the surface water of oceans westwards. This causes upwelling – when deep, cold water rises towards the surface – off the west coasts of all southern hemisphere continents. Essentially, water is pulled away from the coastline, leaving a void which is filled by bottom water which rises to the surface. This upwelled water is not exposed to sunlight until it reaches the surface and is therefore much colder than the surrounding surface water. So, the water is colder along the western coast of Australia.
If the trade winds relax, the strength of upwelling is significantly reduced. This increases the temperature of these western coastal areas, as the cooling effect of the water from lower regions of the water column is reduced, and the Sun has a larger impact in warming the sea surface.
The changes in trade wind strength can, therefore, result in the formation of tropical ocean dipoles.
Affecting the weather
The Indian Ocean Dipole can affect the weather because sea surface temperature in large water bodies affects the temperature and dynamics of the atmosphere above and adjacent to them.
Cold waters cool down the air directly above them, causing the cool, dense air to ‘sink’ downwards and the formation of a high-pressure system. By contrast, warm water heats up the air directly above it. This results in air molecules expanding, becoming less dense, and rising. This uplift brings on a low-pressure system.
These systems then influence the surrounding continental and oceanic regions.
Low-pressure cells—caused when oceans are warmer—are atmospherically unstable, resulting in moist air rising, condensing to form clouds, and precipitating as rainfall. High-pressure cells – caused when oceans are cooler—inhibit rainfall, and result in hot, dry conditions due to the subsidence, when air “sinks” downwards.
The stronger the Indian Ocean Dipole, the stronger these pressure cells.
As of the end of January 2020, the Indian Ocean Dipole index returned to 0. This means that temperatures in the western and eastern tropical Indian Ocean are approximately equal and that the low- and high-pressure systems will lose intensity.
This would signal the end of Indian Ocean Dipole-driven floods here in East Africa and the very hot, dry conditions in Australia, likely for the rest of the season.
However, under climate change, the frequency and intensity of extreme climatic events are increasing. We can, therefore, expect to experience strong 2°C or more Indian Ocean Dipoles more often in the years and decades to come. Basically, climate action needs to be taken yesterday.