South America - Climate. Rivers.

Map   Questions.

Climate. The greater part of South America on both sides ot the Equator lies in the tor­rid zone. The Equator crosses South America in the north and not, as it does Africa, in the centre. A large part of the continent in the south extends beyond the Tropic of Capri­corn and lies in the tem­perate zone. Therefore South America, on the whole, is not so hot a continent as Africa.
If you examine the climate map, you will see that the January temperature almost everywhere in South America is over 20°C above zero. Only in the far south and in the mountains does it drop to 10C.

In July, when it is winter in the Southern Hemisphere, the isotherms bend to the north. The isotherm of 20° C crosses the continent north of the Tropic of Capricorn. In the south the average July temperature varies from 0° to 10° C above zero. Frosts occur in the mountains. Tropical South America on both sides of the Equator is influenced by the trade winds blowing from the Atlantic.
These winds bring heavy rain to both the north-eastern and south-eastern coastal regions and to the Amazon Lowlands. In the equatorial belt the heated currents of air rise, and upon being cooled, cause heavy rains in this region. Rain is heaviest (over 2,000 mm a year) in the western part of the Amazon Lowlands where the moist air is held back by the Andes. The Pacific coast south of the Equator, on the other hand, receives almost no rain, as the trade winds blow from land to sea. There is, besides, a cold current flowing close to the shore that cools the lower layers of the atmosphere and prevents them from rising and causing rain. As the air moves from the cold sea to the land, it is heated and rain does not occur.
In the southern part of South America lying in the temperate zone westerly winds blow from the Pacific. For this reason the west coast receives much rain. The east coast, on the other hand, is shel­tered from the moist westerly winds by the Andes and is, therefore, dry.

Several contrasting climatic regions may be distinguished in South America (Fig. 164).
In the torrid zone lie the Amazon Lowlands. This is a wet equa­torial region. On either side, north and south, lie regions where win­ters are dry and where rain falls mostly in summer. Westwards, along the Pacific coast, lies a dry desert region, extending from lati­tude 5° to 30° S. Further south lie two subtropical regions, with wet summers on the east coast and the La Plata Lowlands and dry summers on the west coast. The southernmost part of the continent lies in the temperate zone. Here the region lying to the east has a desert climate, the one to the west on the Pacific coast, a wet maritime climate. The Andes have an Alpine climate which changes with the altitude and is, therefore, very varied.
Rivers. Most of the large rivers of South America flow into the Atlantic. Owing to the wet climate South American rivers contain very muchwater. As they flow down the ledges of the Brazilian High­lands, many of them form great waterfalls and rapids that hinder navigation. The enormous supplies of water-power are almost unused. South America's greatest river is the Amazon. It ranks third in the world in length (6,480 kilometres together with its tributary, the Ukayali). In size of basin (over 7,000,000 square kilometres) and volume it ranks first. The Amazon rises in the Andes near the Pacific. After cutting through deep gorges it flows across the wet Amazon Lowlands. Here it is joined by its chief tributaries, some coming from the north, others from the south. In its middle course its width is 5 kilometres and its depth 70 metres. In its lower course it reaches a width of over 20 kilometres and a depth of 100 metres.

Fig  165. The Iguassu Falls. One of the world's largest waterfalls in the southern part of the Brazilian Highlands (on the Iguassu, a tributary of
the Parana).

It divides into several channels in places. Its northern and southern tributaries flood at different periods, depending on the rain. The Amazon, therefore, is high-watered throughout the year, though its level is higher after the floods of the larger southern tributaries. In such cases it overflows its banks and floods enormous areas. Upon falling into the Atlantic it forms a great bay with numerous shoals and islands. The tidal waters penetrate far upstream. They cause high waves that tear along with a great noise, flooding the banks of the river. The Amazon is navigable its entire length, from the Atlantic to the Andes.
The second largest and deepest river is the Parana. It rises in the Brazilian Highlands, from where it flows across the La Plata Lowlands into the Atlantic. Its wide estuary is called the Riode
la   Plata. Across the north of the continent flows the Orinoco, forming a large delta at its estuary.
There are many Alpine lakes in the Andes.
Questions and Assignments.
1.                Study the climate map and explain why the western shores of South America at latitude 20"S receive little rain and the eastern "much, while at latitude 45°S, on the contrary, the western shores receive much rain, the eastern little.
2.  Compare the Amazon and Nile as to geographical position, length, size of basin, volume, etc. Account for the great volume of the Amazon.
3.  Mark the names of the South American rivers on the outline map.