Tropical rainfall is shifting northward

This potentially drastic shift could significantly affect regions close to the equator.

Countries situated on both sides of the equator, such as those in Central Africa, northern South America and the Pacific island states, are expected to feel the effects most acutely.

Tropical rainfall shift and atmospheric changes

The northward shift of rainfall was predicted by a research team at UC Riverside led by atmospheric scientist Professor Wei Liu.

The rainfall shift is primarily linked to complex atmospheric changes caused by carbon emissions, which in particular affect the formation of intertropical convergence zones.

The intertropical convergence zones, referred to as atmospheric engines, are responsible for generating approximately one third of global precipitation.

The impact on key tropical crops

Several important tropical crops are cultivated in the regions expected to be most severely affected by the rainfall shift.

Coffee, cocoa, palm oil, bananas, sugarcane, tea, mangoes and pineapples are among the agricultural products that could face production challenges due to unstable rainfall patterns.

However, this northward shift will last only about 20 years. After that, the convergence zones are expected to move back southward and, due to the warming of the southern oceans — another consequence of carbon emissions — remain in that position for nearly a millennium.

Understanding the Intertropical Convergence Zones

Intertropical convergence zones essentially act like a conveyor belt for moisture. In these zones, located along or near the equator, trade winds from the Northern and Southern Hemispheres converge.

The converging air masses rise to cooler altitudes, absorbing large amounts of moisture from the oceans in the process.

As this moist air cools at higher altitudes, thunderclouds form and heavy rainfall occurs. It is not uncommon for tropical rainforests to receive up to 4 metres of rain per year.

Atmospheric Impact of Carbon Emissions

The scientists used advanced computer models to simulate the real-world effects of the continued burning of fossil fuels and other sources of carbon dioxide emissions. Various components of the atmosphere, ocean, sea ice, and land were incorporated into the complex model, with each element interacting with the others.

Professor Liu and his colleagues used these sophisticated computer models to predict the influence of carbon dioxide emissions on the atmosphere.

“The change in precipitation is significant,” said Liu. “This is a region with very heavy rainfall. So a small shift will lead to major changes in the agriculture and economies of societies. Many regions will be affected.

“Essentially, we are trying to simulate the real world. In the model, we can raise our carbon dioxide emissions from pre-industrial levels to a much higher level.

The researchers also accounted for how carbon emissions affect the radiative energy at the top of the atmosphere, shifts in sea ice, fluctuations in water vapour, and changes in cloud formation.

The combined effects of all these factors could shift the rain-producing convergence zones northward by an average of up to 0.2 degrees.

The Impacts of Tropical Rainfall Patterns

In summary, while the consequences of climate change are manifold, the potential short-term shift in tropical rainfall patterns could have far-reaching effects on the agriculture and economies of communities near the equator.

This significant change underscores the urgency of effectively combating global carbon emissions.

The study was published in the journal Nature Climate Change .