Climate

The USA is a land of physical contrasts, including the weather. The southern parts of Florida, Texas, California, and the entire state of Hawaii, have warm temperatures year round; most of the United States is in the temperate zone with four distinct seasons and varying numbers of hot and cold days each season, while the northern tier of states and Alaska have extremely cold winters. The United States has many kinds of climates. The weather ranges from the warm, wet conditions of the Appalachian Highland to the desert conditions of some of the western states. It varies from almost winterless climates in southern Arizona and southern Florida to long, very cold winters in the Dakotas and Montana.

The climate along the northern part of the Atlantic coast is similar to that of England. But in the north central part of the country, summer and winter are worlds apart. There the average difference between July and January is 36 degrees centigrade and more violent extremes are common. The coldest days of a typical January may be 40 degrees centigrade, and the hottest July day may be 45 degrees. This is the sort of climate that is also found in central Asia, far from the moderating influence of the oceans. In the eastern part of the United States, the difference between summer and winter is also very distinct, but not nearly so extreme.

The variations in temperature within the United States have had a marked effect on the country's economy and living standards. There is a long crop-growing season along the south - but in the north it last as long as three months.

West of the Rocky Mountains, running all the way from the Canadian border to Mexico, there are vast areas where almost no trees grow. In this section of the country are the deserts which receive as little as 12.7 centimeters of rainfall a year. Yet, west of the Sierra Nevada Mountains, there are places in which 250 centimeters of rain falls annually.

Although the state of Hawaii is located in the tropical zone, its climate is comfortable because of the ocean currents that pass its shores and the winds that blow across the land from the northeast. The temperature usually remains close to the annual average of 24 degrees centigrade.

Vegetation and animal life

The vegetation of the United States is marked by great diversity.

At the time European settlement began, about one-half of the United States was covered by forests. Today, because of extensive human modification, about 30 percent of the country’s land area is forested Grasslands and other natural vegetative cover decreased as the continent was settled.

Northern Alaska, located in the northernmost part of the United States, is characterized by a windswept tundra., a region of lichens, mosses, hardy low shrubs, and flowering plants. Inland and to the south, the growing season lengthens and certain trees can survive. A few species of needle-leaf trees, notably spruces and firs, dominate a vast but slow-growing evergreen forest, known as the taiga. South of the taiga the growing season is still longer and more tree species can survive. Here is found a mixed forest containing both needle-leaf and broadleaf trees, and including pines, maples, elms, birches, and oaks, as well as hickory, beech, and sycamore.

Still farther south, in western Oregon and Washington, a true rain forest appears as the dry periods shrink to less than a few weeks in midsummer. This luxuriant forest consists primarily of a great variety of needle-leaf trees: Douglas firs, true firs, hemlocks, cedars, spruces, and pines, each occupying its own preferred elevation zone here, and together constituting the second richest forest resource for the nation. The coastal forests of Alaska have fewer species than the rich rain forest to the south but a faster growth than the taiga to the north.

The Gulf of Mexico coast is even warmer and favors the fast-growing pines that now represent the major forest resource of the nation. Other species found here include southern magnolia, pecan, red gum, and black gum (tupelo). A number of subtropical and tropical trees flourish in southern Florida.

Death Valley, which lies below sea level, is but one of the many nearly barren lowlands.