THE EFFECT OF RELIEF (1) How Relief Influences Temperature.—The effect of relief upon the four climatic elements is more easily seen than is the effect of land and sea. Everyone knows that the temperature changes from the base of a mountain to its top. At the base the air may be so warm that the lower slopes are shrouded in tree ferns, graceful palms, twining creepers, and other tropical growths. Higher up the vege tation consists of the broad-leaved trees of the temperate zone. At the top the air is so cold that wastes of naked rock lie close to perpetual snow like that which shrouds the Andes even at the equator.
In tropical lands the temperature becomes more and more favor able to human activity up to a height of about 5000 or even 10,000 feet. Only at such altitudes does the air gain something of the stimu lating quality which is so beneficial to health and energy in tem Aerate lands. This is shown in the location of the capitals of the South American republics. Most of them are at altitudes of five to ten thousand feet, that of Mexico City, for example, being over 7000. Even Brazil has decided at some time to remove the capital from beautiful Rio de Janeiro to the interior on the Brazilian plateau. imilarly the summer resorts, recreation centers, and sanatoriums "for white people in India are "hill stations" at high altitudes. Simla, among the Himalayas, 7500 feet above the sea, is becoming more and more fully the summer capital of the country. In the Philip pines the hill station of Baguio is gradually assuming a similar im portance. Without it many American officials and their families would have to leave the islands in order to recover their health. In high latitudes, on the contrary, the highlands are usually too cold to support many people. In Norway, for example, the central highland is inhabited only by a few Laps. I.'" (2) Relief and Atmospheric Pressure.—The effect of relief upon atmospheric pressure is important chiefly in relation to rainfall. As winds blow up a slope the air expands because of a decrease of pres sure. Thus it grows cool and gives up rain.? (3) How Relief Changes the Course of the Winds.—One of the most important ways in which relief influences climate is through move ments of the air. This is because highlands and mountains often change the direction of currents of air, and prevent certain winds from blowing in protected placKs. For instance, the maritime Alps and the northern Apennines shield the Riviera from the cold north winds. Hence this region on the Mediterranean coast north of the Gulf of Genoa rarely experiences frost even in January, while at Portland, Maine, in the same latitude, the ground is sometimes cov ered with snow for fivesolid months. The Swiss and Italian Alps
in similar fashion protect the Italian Lake region. Lemons and olives grow there in the latitude of Diffalo or even St. Paul and Minneapolis. The mild winters and beautiful scenery of both the vRiviera and the Lake region attract pleasure seekers and invalids from all over Europe. The presence of a great number r;if people with plenty of money and nothing to do has caused Monte Carlo, in the little principality of Monaco, to become the most famous gam bling resort in the world. All these results are due largely to the fact that the Alps by'shutting off the winds from the north, prevent cold waves like those which in our own country sweep across the plains and sometimes kill the orange trees even as far south as Floy,ida.
The Himalayas in the same way cause northern India to be warmer than the parts of China in the same latitude. For instance, Delhi, the capital of India on the Jumna, lies in about the same latitude as Hankow, the commercial center of China on the Yangtse, but its January temperature averages 58° while that of Hankow is 39°.
How Relief Permits Orange Growing in Northern California.— The effect of relief upon movements of the air and thus upon temper ature can be seen not only in great contrasts like that between India and China, but in small contrasts between places only a few miles apart. For instance, in California at the western base of the Sierra Nevadas in a latitude as far north as Philadelphia, there are many small valleys where oranges ripK, although in other valleys close at hand they will not ripen at all. In fact the oranges ripen earlier in some of these northern valleys than in the region around Los Angeles, 400 miles jarther south. here are several reasons for this, but all are connected with the relief. (1) The valleys are so located that they face the southwest and thus receive abundant warm sunshine. (2) They are protected from cold winter winds from the interior by the high Sierras immediately to the east. (3) When air grows cool at night it contracts and therefore becomes comparatively heavy. Hence in these valleys instead of remaining and becoming so cool that frost occurs, the air drains away because of the relief. Its place is taken by air which is warmed by descending from above. Where the slopes are favorable there may be no frost, although ice forms not far away in the hollows where the cold air comes to rest. Wherever there is danger of frost wise farmers take advantage of air drainage if their farms are on slopes. They plant their peach and apple orchards, for example, on the warmest slopes where late spring frosts will not nip the blossoms.