Climate and weather

Mountains.

North of the Central Lowland, extending for almost 994 miles, are the five Great Lakes⁴ which the United States shares with Canada. The majestic Rocky Mountains stretch all the way from Mexico to the Arctic. They are high, sharp and rugged.⁹ In the days when gold was king and thousands of men lived in the mining camps in the wilderness, agriculture began in the Rockies. In this land of little water, farming was very difficult — and would have been impossible without a series of irrigation canals that bring water from the high mountain streams to the dry valleys below.

Not counting patches of cultivated soil, there are still about 130,000 square miles of desert between Salt Lake City, Utah, and Reno, Nevada. Here, there is nothing but dead lakes, dry rivers, snakes and small animal life, enormous mineral wealth, and the beauty of the desert. In the vast triangle of land between the Sierra Nevadas to the west and the Rockies to the east, the climate is so dry and hot that even fairly large rivers from the mountains evaporate so rapidly that they die before reaching the end of the desert.But even in the vast, silent desert there are rich oases — prosperous towns which were built where men found sufficient water.

On arriving in America Europeans had to learn to cope with the variety of unfamiliar climates and vegetation. European climatic experience was not a very useful guide for survival in America. That was especially true in the subtropical South and the arid West¹, regions that provided unexpected opportunities but also posed obstacles for which there were no obvious analogies in the Old World.

Europeans expected America to be much the same, as America faced the Atlantic, just like Europe. The truth was quite different. America's western air comes not from the ocean, as in Europe, but from the continental interior which is extremely cold in the winter and ovenlike in the summer.

The northernmost zone, adjacent to the Canadian border, is a region of northern forest that stretches from Maine across northern New England and the upper Great Lakes. Here the growing season is very short, and the winters are long and fiercely cold. For farmers it has always been miserable country.

Southward the temperature moderates. The growing season is longer, winters are milder, and summers are hot. Settlers discovered that they could grow most of the crops they had known in the Old World and a variety of New World crops as well. Because American summers were considerably hotter and longer than in Europe, Amer­ican crops often yielded a larger harvest. It was here that America first developed its reputation abroad as a land of plenty.

Still farther southward one crosses an invisible but crucial line called the Mason-Dixon Line. The central features of Southern climate are hot humid summers and a long growing season. The climate is i good for a variety of valuable subtropical crops, such as indigo, rice, and cotton. The cotton monopoly of the American South came to an end in the early twentieth century as a result of competition from Indian and Egyptian cotton.

The climate of the Central Basin is rather moderate. Moist and dry years alternate. At the time of the native prairie, before the settlers came, the soil had been protected by a dense layer of turf. Intensive plowing exposed the cultivated soil to the wind and to the storms, and the harvest in dry years gets completely ruined.

Further west, in the semi-arid region of short grass where farms and cattle ranches begin, the situation is even more precarious. In years when rain is plentiful, the prairie grasses grow well and the herds of cattle grow fat. But during frequent droughts large herds of cattle suffer and may even die. Blazing summer heat dries up what little moisture is available, and in winter arctic temperatures and howling blizzards make life hard. The first farmers and ranchers had to learn climatic laws the hard way.

The only substantial humid region in the western United States is wedged into a narrow strip between the Pacific coast and the Sierra-Cascade ridge line.² Unlike the East, with its continental extremes of summer and winter temperature, West Coast temperatures are moderated all year long by westerly winds from the ocean so that the entire coast from Canada to Mexico enjoys cool summers and mild winters.

West Coast rainfall patterns also differ from those in the East, and those differences impart a special personality to the Pacific Coast

climate. In the humid East rainfall is taken for granted since most places get plenty of rain year round. This is not true in the West, however, where rainfall differs significantly from place to place and from season to season.

To begin with, rainfall diminishes gradually from north to south. Thus western Washington and Oregon receive enough rain to support forests of tall, straight, fast-growing, evergreens. By contrast, central California is noticeably drier, with low trees and open grasslands that are well adapted to drought. In southern California, the climate is technically defined as semi-arid and true desert lies not far beyond the city limits of Los Angeles and San Diego.

On the West Coast, winter is the rainiest time everywhere, and summers almost everywhere are very dry. Under natural conditions brushfires are part of the natural ecological cycle, and periodic burning keep brush down and grasslands open. But when fires get started in California cities — and it is impossible to prevent them all — they can be devastating.

Despite drought and fire, Americans have found California's Mediterranean climatic zone a particularly alluring place. Near the coast summers are cool and pleasant, and even the mild rainy winter is often not very rainy, except in the far north. The combination has attracted both tourists and permanent residents from harsher climates in the North and East.

The unusual combination of wet winters and dry summers, moreover, makes it possible to grow crops that will not mature anywhere else in the country, with the result that California has the most lucrative agricultural industry in America.

Perhaps the most common feature of America's western climates, however, is the enormous variation to be found within very small areas. Much of the mountainous West contains such enormous variety within such small distances that it is broken into a mosaic of microclimatic regions. So the large variety of geographic and climatic environments in America guaranteed that people in America would find both oppor­tunities and challenges that would be denied to people in less favored parts of the earth. The country's riches rewarded luck and hard work, and its geographic and climatic variety rewarded those who were capable of adapting to new circumstances.

Дата добавления: 2015-04-24