In the United States right now, a “bomb cyclone” weather system is dominating the headlines and rightfully so. Blizzard conditions with winds approaching minimum hurricane speeds are affecting parts of the interior U.S. The attention is certainly warranted as “bombogenesis,” a pressure drop of 24 mb in 24 hours, is somewhat rare in the Plains. However, something else caught my attention this week also. The African continent is simultaneously experiencing two extreme weather-climate phenomena: Tropical cyclone Idai on east coast and a Saharan dust event on the west coast.
Tropical cyclone Idai is a potent storm headed directly toward Mozambique. Aon meteorologist Steve Bowen tweeted this week,
Prior to developing into #CycloneIdai, the initial low spawned torrential rain in Malawi & Mozambique. Already responsible for 40+ fatalities & 400+ injuries. A Cat 3 landfall in #Mozambique (surge, wind, inland flood) would create severe challenges for local infrastructure.
After impacting Mozambique and Malawi, the initial disturbance intensified into a major tropical cyclone as it moved over warm waters of the Mozambique channel separating Madagascar from the southeast African coast. Wind shear in the region has also been favorable (low) for intensification. According to meteorologist Chris Dolce at Weather.com, "There have been only three tropical cyclones that have made landfall in Mozambique at that intensity or stronger since the use of satellites began in 1966, according to NOAA."
The population of Mozambique is concentrated at the coasts as is much of its economic activity. Vulnerability to these storms is typically some function of exposure to the event, sensitivity, and adaptive capacity or ability to bounce back (graphic below). Exposure to a potential category 2 or 3 level tropical cyclone making landfall on Thursday creates elevated vulnerability because of increased sensitivity (people and infrastructure) and low adaptive capacity. More than 80 percent of the population of Mozambique lives on less than two dollars per day.
As the eastern coast of Africa faces hazards associated with a tropical cyclone, many West African countries have been dealing with significant dust storms. Professor Greg Jenkins is a professor at Pennsylvania State University and a leading international expert on West Africa climate. Jenkins, director of Penn State's Alliance for Education, Science, Engineering and Development in Africa (AESEDA), posted NASA satellite images of dust over West Africa (top) and aerosol optical depth (bottom) earlier this week. Aerosols are tiny suspended liquid or solid particles in the atmosphere. The amount of aerosols in a column of the atmosphere can significantly affect how the atmosphere reflects, scatters, or absorbs visible and infrared energy. Aerosol optical depth (AOD) is a way to quantify that impact.
Dust events like the current episode in West Africa are common in the spring and summer. According to studies, over 60 percent of Saharan dust is blown southward into West African countries. They can cause acute upper respiratory illness, cardiovascular issues, infectious disease dispersion, or even maternity-reproduction challenges. Saharan dust often travels long distances across the Atlantic Ocean and affects people in the Caribbean Islands, South America, and North America.
Saharan dusts can stifle crop yields through reduced photosynthesis, seedling burial, and plant tissue loss, but the World Meteorological Organization (WMO) also highlights some positive benefits. The WMO website notes that Saharan dust "is thought to fertilize the Amazon rainforest, and dust transports of iron and phosphorus are know to benefit marine biomass production in parts of the oceans suffering from the shortage of such elements." Saharan dust can also impact the development or intensification of hurricanes.
Africa is simultaneously experiencing hydro-climatological extremes on both sides of the spectrum, wet and dry. While fascinating and interesting from a meteorological perspective, both of these events pose a threat to one of the most populous continents on the planet. Some of us are paying attention to them too.
