Washington: A changing rainfall pattern may deprive a billion people of fresh water in the tropics and subtropics in the coming decades, according to the latest research.
The rain band near the equator that determines the supply of such fresh water has been creeping northwards for more than 300 years.
If the band continues to migrate at just less than a mile a year -- the average for all the years it has been moving north -- then some Pacific islands near the equator, even those that currently enjoy abundant rainfall, may be drier within decades and starved of fresh water.
The prospect of additional warming because of greenhouse gases means that the situation could happen even sooner.
The findings suggest "that increasing greenhouse gases could potentially shift the primary band of precipitation in the tropics with profound implications for the societies and economies that depend on it."
"We're talking about the most prominent rainfall feature on the planet, one that many people depend on as the source of their freshwater because there is no groundwater to speak of where they live," said Julian Sachs, professor of oceanography at the University of Washington (UW) and lead author of the paper.
The band of rainfall happens at what is called the inter-tropical convergence zone. There, just north of the equator, trade winds from the northern and southern hemispheres collide, at the same time heat pours into the atmosphere from the tropical sun.
The new study presents surprising evidence that the inter-tropical convergence zone hugged the equator some three and a half centuries ago during Earth's little ice age, which lasted from 1400 to 1850.
The authors analysed the record of rainfall in lake and lagoon sediments from four Pacific islands at or near the equator.
These findings were published in the July issue of Nature Geoscience.
First Published: Monday, August 10, 2009, 11:22