Trinidad and Tobago’s proximity to the equator results in two distinct climate types, producing opposing wet and dry seasons. Variations in these climatic seasons between the islands are primarily due to differences in land size, topography, elevation, trade wind orientation, and geographical location.
The country’s daily temperature cycle is more pronounced than its seasonal cycle. The long-term mean (1971–2000) annual maximum and minimum temperatures are 31.3°C and 22.7°C, respectively, with a mean daily temperature of 26.5°C. Generally, wet season temperatures are warmer than those in the dry season, with September being the warmest month in the wet season and March the warmest in the dry season.
Annually and seasonally, Trinidad experiences more rainfall than Tobago. However, both islands exhibit a distinct bimodal rainfall pattern, with early (June) and late (November) season maxima. Trinidad’s primary rainfall peak occurs in June, while Tobago’s occurs in November.
The Role of the Saharan Dust Layer
The nation’s rainfall pattern, coupled with Saharan dust, presents both challenges and benefits. The Saharan Air Layer, commonly known as Saharan dust, consists of sand, dirt, and other particles lifted into the atmosphere from the vast North African desert. This dust is transported westward across the Atlantic Ocean via African Waves.
The Saharan Air Layer is a well-mixed, dry pocket of air residing between 5,000 and 15,000 feet above sea level. Since tropical cyclones require a deep feed of moisture for development, Saharan dust often inhibits storm formation. Once a dust pocket moves westward over the Atlantic, it becomes trackable via infrared satellite imaging. Forecast models combine predicted dust movement with precipitation rates and pressure contours to depict the Saharan Air Layer’s trajectory.
00Z Thursday, January 2nd, 2025, NASA GEOS-5 Dust Extinction Monitoring Tropical Atlantic Dust Aerosol Optical Depth showing Saharan Dust. (Weathermodels.com)
The impact of Saharan Dust on health and the environment
Saharan dust haze significantly affects air quality in Trinidad and Tobago, leading to increased pollution levels. Health impacts include respiratory and cardiovascular issues, as well as eye infections. Environmental effects include the absorption of both longwave and shortwave radiation, contributing to localised heating by warming the dust-laden atmosphere.
DUST INDEX FORECAST Legend and Meta Data (metproducts.gov.tt)
Saharan Dust over time
Research published in Science Advances reconstructs the African dust plume over the past 23,000 years. Findings indicate a dramatic reduction in dust levels around 11,000 years ago. Scientists suggest this weakened plume allowed more sunlight to reach the ocean, raising temperatures by 0.15°C—a small but significant increase that likely contributed to intensified monsoons over North Africa.
“In the tropical ocean, fractions of a degree can cause significant changes in precipitation patterns and winds,” says co-author David McGee, Assistant Professor at MIT’s Department of Earth, Atmospheric and Planetary Sciences.
“It seems dust variations may have large enough effects that understanding their impact on past and future climates is crucial.”
The journey of Saharan Dust
The most significant pulses of Saharan dust occur between February and October. The north-easterly Harmattan winds lift approximately 182 million tonnes of dust annually, carrying it beyond the Sahara’s western edge. This is equivalent to 689,290 dump trucks filled with dust. As it travels 2,500 km across the Atlantic, some dust falls to the surface or is washed from the sky by rain. Near the eastern coast of South America, 132 million tonnes remain airborne, while 27.7 million tonnes—enough to fill 104,908 dump trucks—settle over the Amazon Basin.
The Amazon’s dependence on Saharan Dust
Despite its negative perception, Saharan dust plays a crucial role in fertilising the Amazon rainforest. It is rich in phosphorus, an essential nutrient for plant growth. Amazonian soils lose up to 90% of their phosphorus through rainfall, which washes the nutrient out to sea. While decomposing plant matter helps recycle some phosphorus, Saharan dust provides a vital external source. Without this continuous input, the biodiversity of the Amazon would be adversely affected.
Additionally, around 43 million tonnes of dust settle over the Caribbean Sea, directly impacting regional air quality. The iron-rich red hue of Saharan dust feeds phytoplankton along the Caribbean and southeastern US coasts. Phytoplankton photosynthesis is responsible for producing half of the world’s oxygen and absorbing half of the planet’s carbon dioxide.
Saharan Dust and hurricane suppression
Saharan dust plays a key role in suppressing hurricane formation in the Atlantic Ocean. During summer, dust storms depart the African coast every three to five days, forming a layer of hot, dry air known as the Saharan Air Layer. This layer influences rainfall as far as California.
Dust storms suppress hurricanes in three key ways:
- Dry air – The middle layers of the atmosphere become too dry for storms to develop.
- Vertical wind shear – The strong winds embedded within dust storms disrupt the formation of storms.
- Dust particles – Scientists believe dust inhibits cloud formation, preventing tropical waves from intensifying.
Additionally, the dust acts as a shield, blocking sunlight from reaching the ocean surface. In some cases, this cooling effect reduces sea temperatures by as much as 1°C.
Saharan Dust and coral reef decline
While Saharan dust benefits the ocean, research from NASA suggests it may contribute to coral reef declines in the Caribbean. Coral reef deterioration is often attributed to pollution, sedimentation, and rising water temperatures linked to the North Atlantic and El Niño-Southern Oscillation events. A 1999 Science article by Harvell et al. reported a global increase in coral bleaching severity during the 1997–98 El Niño period.
Some scientists argue that coral reef disease persists even in isolated, unpopulated areas. Geologist Gene Shinn suggests that, while elevated sea temperatures from El Niño caused widespread coral bleaching, other environmental factors, such as Saharan dust, may also play a role.
00Z Saturday, August 3rd, 2024, NASA GEOS-5 Dust Extinction Monitoring Tropical Atlantic Dust Aerosol Optical Depth showing Saharan Dust.
Saharan dust is far more than just a seasonal nuisance. With its storm-fighting capabilities, fertilising power, and role in oxygen production, these airborne visitors from the Sahara are integral to the planet’s biodiversity. However, their impact on air quality remains a pressing concern for Caribbean populations. Understanding the dual nature of Saharan dust is crucial for managing both its benefits and its challenges.
This story was published with the support of the Caribbean Climate Justice Journalism Fellowship, a joint venture between Climate Tracker Caribbean and Open Society Foundations.
