CLIMATE OF SOUTH AMERICA.—For various reasons the climate of South America differs greatly from that of North America. Both continents taper to the south, with the result that of the latter only a small part lies within the tropics, while of the former less than one-fifth falls beyond them. North America, moreover, extends well within the Arctic Circle; while the extreme point of South America is distant by almost eight hundred miles from the Antarctic Circle. The result is that, whereas in the northern continent only a small area has a mean temperature above 60° F. during the coldest months of the year, the mean temperature of more than two-thirds of the southern continent does not fall below that point during the corresponding season. The range of temperature is, therefore, much less in South America than in North America, and the typical continental climate is developed to a much less extent.
During the southern summer the region of highest temperature lies in the north-eastern part of the continent, south of the equator, and the isotherms over a greater part of north-eastern South America are therefore convex to the south. Over the remainder of the continent, they run from north-west to south-east as the result of the cold current along the Pacific coast, winds from which tend to lower the temperature of the adjacent lands. During the northern summer, when the region of greatest heat lies north of the equator and east of the Andes, the isotherms run from north-west to south-east in that part of the continent, but south of the equator they run from east to west, except on the Pacific coast, where for the same reasons as before they turn towards the north. Over the greater part of South America the heaviest rainfall takes place during the wannest months of the year. An area of low pressure is de veloped to the south of the equator during the southern summer ; the trade winds of the northern hemisphere are sucked into the basin of the Amazon, and these winds, blowing from the north-east, north, and further south from the north-west, bring much rain to the lowland regions over which they blow. At the same time, the south-east trade winds are drawn into the Paraguay-Parana basin, so that the whole of the lowland area from the mouth of the Amazon to that of La Plata, and westward towards the Andes, has a heavy precipitation. Along the north-east of the Brazilian
highland the rainfall is less, as the south-east trade winds are blowing parallel to the coast ; while along the south-east coast of the upland the rainfall is heavier, but does not extend far inland. The west coast of the continent is without rainfall from the equator as far south as Valdivia, beyond which point much moisture is brought to the coast by the westerly winds. That part of South America which lies north of the equator receives its heaviest rainfall during the northern summer, the winter precipitation of that region being reduced by the fact that the trade winds from the North Atlantic are pulled onwards to the area of low pressure south of the equator. There is also, during this season, a monsoonal rainfall on the west coast of the northern part of the continent. South of the equator, where winter conditions prevail, the amount of moisture deposited is generally much less than during the summer months. The south eastern trade winds are pulled northwards, and, except along the coast, more especially between Rio de Janeiro and Buenos Aires, the rainfall is low. On the west coast, the strip which now receives rain extends almost as far north as La Serena.
To sum up, the greater part of the Amazon lowlands has a mean annual rainfall of over 80 inches, and this amount is also received along part of the north-east coast north of the mouth of the Amazon. The remainder of the region which, roughly speaking, lies east of a line drawn from Quito to Buenos Aires, has between 40 and 80 inches, with the exception of the central part of that district which is east of the longitude of Para, where it is much less. To the south-west of the line already indicated, precipitation rapidly decreases and a dry belt stretches across the continent from Peru to south-east Patagonia. South of Concepcion the rainfall along the west is heavy, rising in places to over 80 inches.