Does population affect the climate?

COULD it be that Africa (and other parts of the third world) are being literally dried out by populations growing at record rates? Put it another way: Is population growth changing the climate in Africa?

Lester Brown, the scholarly, low-key president of the Washington's Worldwatch Institute and editor of the book ``State of the World 1985,'' thinks this may well be so.

He cites agricultural, meteorological, and hydrological evidence, although he is careful to add the caveat that the data are ``rather persuasive,'' not conclusive.

Disagreeing with that theory are other experts such as Jon Tinker, editor of Earthscan, the publication arm of the International Institute for Environment and Development.

``Lester Brown states the theory expertly,'' Mr. Tinker says, ``but it's just that -- a theory. We just don't know for sure.''

Recent reports in Science magazine in the United States also suggest that previous droughts lasting 15 to 20 years were not man-made, and that rain eventually returned.

Mr. Brown himself agrees that meteorologists tend to dismiss his views on the ground that ``forces driving global atmospheric circulation would override any local, human-induced alterations.''

He cites the following, however:

In Manaus, in the Brazilian rain forest, deforestation dramatically changes what happens to rainwater.

Normally, 25 percent of rain evaporates and almost 50 percent reenters the atmosphere via transpiration from vegetation. The rest is runoff.

When land at Manaus was deforested, three-quarters of the rainwater ran off, and only one-quarter was evaporated or transpired.

Less moisture in the atmosphere means less rain.

Brown says that a United States National Academy of Sciences study estimates that in the Sahel -- the eight-nation region in north central Africa, running from Chad to the western edge of the continent and including the Cape Verde Islands -- one-third to two-thirds of all rainfall comes from moisture evaporated from the land.

As land is turned from forest into cropland and desert, it reflects more sunlight back into space.

Some scientists believe this causes large masses of drier air to lie closer to the ground.

In the Sahel, with its growing populations and reduced numbers of nomadic tribes, desert is expanding fast.

The water levels in the Senegal, Niger, and Chari Rivers in the Sahel have dropped sharply in recent years, along with that of Lake Chad.

Canadian meteorologist F. Kenneth Hare, analyzing desertification in Africa in May 1984, concluded: ``For the first time we may be on the threshold of man-induced climatic change.''

Brown believes that ``the time may have come'' for political leaders and aid agencies to consider the possibility seriously.