The Book

Climate, Flora, and Fauna

CLIMATE

The classical system of climatic classification divided the earth into latitudinal zones based on the important parallels and on the length of the day, thereby creating tropical, subtropical, temperate, subarctic, and arctic zones. The Tropics range from the equator (0) to the tropic of Cancer in the northern hemisphere and to the tropic of Capricorn in the southern hemisphere, which are, respectively, at 2327' north latitude and 2327' south latitude from the terrestrial equator. These latitudes correspond to the northernmost and southernmost declinations of the sun's ecliptic to the celestial equator.

Myanmar, with a southernmost latitude of approximately 945' north and a northernmost latitude of roughly 2820' north, would therefore fall into both the tropical and subtropical zones of the northern hemisphere. Given that the tropic of Cancer, the northern border of the Tropics, traverses the country some one hundred miles north of Mandalay, the land north of the tropic of Cancer-almost half the total land mass of Burma-would be considered subtropical, if we follow the old classification of climatic zones.

Again according to the old classifications, climates within any particular zone should be somewhat uniform. But this is not at all the case as far as the tropical zone of Burma is concerned. As noted in the previous chapter, there are wet zones in the south and a dry, almost arid zone to the north, between Pyay, Mandalay, and Bagan. And how do we explain the fact that the wet, fertile delta area around Yangon is at the same latitude as the arid, desolate southern part of the Sahara Desert when both areas are part of the Tropics in the northern hemisphere?

Modern classifications of climate zones take into account several variables, such as temperature, precipitation, humidity, altitude, and soil formation, among others. These zones have usually been established on the basis of the response to climate or weather by some climate-dependent phenomena. Natural vegetation is such a phenomenon that very much depends on climate. It is like an instrument for measuring climate. The most prevalent classification used for climatic groupings today takes account of vegetation-for example, rainforest, savanna, taiga, tundra, and desert. The type of vegetation is determined by several factors, such as temperature, humidity, precipitation, soil condition, and altitude, but the first three are the most closely related to the prevailing winds in the climatic zone. My Hawaiian friends know such a wind system very well-the Pacific trade winds, which are part of the global air circulation system.

Myanmar, however, lies outside the trade wind area and, together with India and Indochina, is dominated by a different wind system, called "monsoon." It is often assumed that monsoon is synonymous with rain, or rainy season, but it is instead a wind system. The monsoon wind blows from colder to warmer regions and therefore reverses its direction seasonally. In the case of Burma, the monsoon blows from sea to land from May through October and from land to the sea from November through April. What is called the summer monsoon has a southwesterly direction and, as water vapor condenses in the rising air, it brings plentiful rain; however, the intensity and duration vary from year to year. What we call the winter monsoon, by contrast, has a prevailing northeasterly direction and brings very little rain. While the temperate regions of the world experience four distinct seasons, Burma is different in that it has just three seasons, during which temperature and vegetation change considerably less than in the temperate regions. A rainy season that lasts from May through October is followed by a cool and dry season from November through February, then the months of March and April are hot and dry.

Wind systems also influence ocean surface circulation, and in the monsoon zone surface circulation reverses every half year and features two opposing gyres. As far as tides are concerned, southern Burma, on the Andaman Sea, has daily, not twice daily, tides. For Myeik (formerly Mergui) and Yangon, high tide reaches about seventeen feet (five meters), which is considerable but not as dramatic as some ports on the Atlantic coast of Canada where high tide reaches an impressive sixty feet (nineteen meters).

Myanmar receives most of its annual rainfall during the rainy season when the southwest monsoon, coming from the Bay of Bengal and the Andaman Sea, first hits the coastal areas, that is, the delta area around Yangon, the northwest Rakhine State (close to Bangladesh), and the Tanintharyi coastal strip along the southern border with Thailand. The last two areas have high mountain ranges behind them and as a consequence receive some of the heaviest rainfall in the world. Sittwe (formerly Akyab), the capital of Rakhine State, receives some 208 inches (5,200 millimeters) of rain annually, over 90 percent of which falls during the rainy season (May through October). People living outside the Tropics commonly believe that rainy season brings rain continuously, for days and weeks, but this is usually not the case. Monsoon rains fall mainly in the late afternoon and in the evening, when it seems that the heavens' floodgates have opened for an hour or so. Although the monsoon rains are indispensable for agriculture, it is during this season that heavy flooding and disastrous destruction can occur in various parts of the country.

The amount of annual rainfall varies sharply in the various parts of the country, attributable in large part to topography. While Sittwe receives the most rain, at over 200 inches, other areas still receive appreciable amounts of annual rainfall, such as Mawlamyine (formerly Moulmein) in the south-about 175 inches (4,400 millimeters); the delta area and Yangon-100 inches (2,500 millimeters); the Shan Plateau-60 inches (1,500 millimeters); and the dry area around Bagan-less than 36 inches (900 millimeters).

Temperatures also vary considerably in the different parts of Burma and can reach a staggering high of 116 F (45 C) in the dry central area during the hot season. In colonial times, the hot season was the time when the colonial officials, traders, and miners took their families to the cooler places in the Shan hills, to Pyin Oo Lwin (formerly Maymyo), and to Kalaw. On the Shan Plateau itself, temperatures can drop to near freezing at night. In Yangon, the average monthly temperature in January is around 76 F (25 C), whereas Bhamo, in Kachin State, will register only 60 F (16 C). My last destination on the second trip to Burma was Myitkyina, in the Kachin Hills, where the warm jacket I had bought in Yangon was most useful in the cool evenings.


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