Tropical Rains To Shift Northward Due to Climate Change, Affecting Agriculture in the Coming Decades

Computer modeling indicates a northward rain shift spurred by carbon emissions that could affect agriculture and economies near the Earth's equator.

Northward Tropical Rain Migration

A team of University of California- Riverside atmospheric scientists is predicting that tropical rains will shift northward because of the formation of the intertropical convergence zones as a result of unchecked carbon emissions.

Led by climate change and sustainability associate professor Wei Liu, the experts ran sophisticated climate model simulations to investigate the atmospheric influence of carbon dioxide emissions through continued burning of fossil fuels. It is this result that their study brings into discussion in the paper titled "Contrasting fast and slow intertropical convergence zone migrations linked to delayed Southern Ocean warming."

The authors have used a very comprehensive model of climate that contains a number of atmospheric, land, ocean, and sea-ice components interacting among themselves so as to show the possible change that can happen within the Earth's atmosphere.

In the simulation, it factored in how carbon emissions would alter the amount of radiant energy at the top of the atmosphere. It further took into account changes in cloud formation, water vapor, and sea ice.

These elements, among other factors, translated to environmental conditions that are likely to force the rain-forming intertropical convergence zones northward by as much as 0.2 degrees on average.

Liu and his colleagues wanted to model real-world conditions. Fortunately, the model allowed them to increase carbon dioxide emissions from pre-industrial levels to much larger values.

Results showed that the regions most affected by this northwards shift would be tropical regions lying on either side of the equator. Such areas include central African nations, northern South America and pacific island states. It would hence affect the major crops being grown in the tropics such as pineapples, mangoes, tea, sugarcane, banana, palm oil, cocoa, and coffee.

This rainfall change, according to Liu, was very vital because the tropics receive heavy rainfall. Even a small shift will lead to big changes in agriculture and the economy of the affected communities. In short, many other regions could also get affected.

The northward migration, however, will only prevail for two decades. This is because stronger forces from the warming southern oceans will drag the convergence zones southward and lock them in place for a millennium.

What Is the Intertropical Convergence Zone?

The intertropical convergence zone refers to the area along or near the equator where trade winds from the northern and southern hemispheres meet. Trade winds are shot upward into the cooler elevations; huge volumes of soaked moisture are sucked up from the oceans.

The ITCZ is viewed as a band of clouds containing showers and occasional thunderstorms that circles the earth near the equator. Although the solid band of clouds may extend for several hundreds of miles, it can be broken into smaller line segments.

As elevation increases, moist air cools resulting in thunderstorms to build up and pounding rainstorms. This can be why tropical rainforests get as much as 79 to 394 inches (200 to 1,000 centimeters) of rain within a year.

The location of the intertropical convergence zones varies throughout the year because, following the Sun, it shifts north in the Northern Hemisphere during summer and south during the winter.

Accordingly, the ITCZ causes wet and dry seasons in the tropics. These zones also turn out like atmospheric engines that, in effect, drive about one-third of the world's precipitation.