Page 318 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

282 part II The Water, Weather, and Climate Systems
Climates greatly influence ecosystems, the natural, self-regulating communities formed by plants and ani- mals in their nonliving environment. On land, the basic climatic regions determine to a large extent the location of the world’s major ecosystems. These broad regions, with their associated soil, plant, and animal communi- ties, are called biomes; examples include forest, grassland, savanna, tundra, and desert. Discussions of the major ter- restrial biomes that fully integrate these global climate patterns appear in Part IV of this text (see Table 20.1). In this chapter, we mention the ecosystems and biomes associated with each climate type.
tropical Climates (tropical latitudes)
Tropical climates are the most extensive, occupying about 36% of Earth’s surface, including both ocean and land areas. The tropical climates straddle the equator from about 20° N to 20°S, roughly between the Tropics of Cancer and Capricorn— thus the name. Tropical climates stretch northward to the
tip of Florida and to south-central Mexico, central India,
and Southeast Asia and southward to northern Australia, Madagascar, central Africa, and southern Brazil. These climates truly are winterless. Important causal elements include:
• Consistent daylength and insolation, which produce consis- tently warm temperatures;
• effects of the intertropical convergence zone (ITCZ), which brings rains as it shifts seasonally with the high Sun;
• Warm ocean temperatures and unstable maritime air masses.
tropical rain Forest Climates
Tropical rain forest climates are constantly moist and warm. Convectional thunderstorms, triggered by local heating and trade-wind convergence, peak each day from midafternoon to late evening inland and earlier in the day where marine influence is strong along coastlines. Precipi- tation follows the migrating ITCZ (review Chapter 6), which shifts northward and southward with the Sun throughout the year but influences tropical rain forest regions all year long. Not surprisingly, water surpluses in these regions are enormous—the world’s greatest streamflow volumes occur in the Amazon and Congo River basins.
High rainfall sustains lush evergreen broadleaf tree growth, producing Earth’s equatorial and tropical rain for- ests. The leaf canopy is so dense that little light diffuses to the forest floor, leaving the ground surface dim and sparse in plant cover. Dense surface vegetation occurs along riverbanks, where light is abundant. (We examine wide- spread deforestation of Earth’s rain forest in Chapter 20.)
Uaupés, Brazil, is characteristic of tropical rain forest. On the climograph in Figure 10.3, you can see that the month of lowest precipitation receives nearly 15 cm and the annual temperature range is barely 2 C°. In all such climates, the diurnal (day-to-night) temperature range exceeds the annual average minimum–maximum (coolest to warmest) range: Day–night differences can range more than 11 C°, more than five times the annual monthly average range.
CRITICalthinking 10.1 Finding your Climate
Using Figure 10.2, locate your campus and your birth- place, and determine the associated climate type for each. Use the Internet to find temperature and precipi- tation data for those places. (Climatological records for Canadian stations can be found at climate.weather .gc.ca/climate_normals/). Next, refer to appendix B to de- termine the climate types for these places in the köppen classification system. Briefly show how you worked through the köppen climate criteria to establish the cli- mate classification for your locations. •
Yangon, Myanmar
Uaupés, Brazil
Tropical rain forest Tropical monsoon
Arusha, Tanzania
Tropical savanna
Tropical climates have three distinct regimes: tropical rain forest (ITCZ present all year), tropical monsoon (ITCZ present 6 to 12 months annu- ally), and tropical savanna (ITCZ present less than 6 months).
The only interruption in the distribution of tropical rain forest climates across the equatorial region is in the highlands of the South American Andes and in East Africa (see Figure 10.2). There, higher elevations produce lower temperatures; Mount Kilimanjaro is less than 4° south of the equator, but at 5895 m, it has permanent glacial ice on its summit (although this ice has now nearly disappeared due to increasing air temperatures; see Figure HD 17c). Such mountainous sites fall within the highland climate category. A unique tropical summer-dry pattern falls with the rain shadow of the mountains on Kauai as pictured in Figure 10.25, page 305 at the end of this chapter.
tropical monsoon Climates
Tropical monsoon climates feature a dry season that lasts 1 or more months. Rainfall brought by the ITCZ falls in these areas from 6 to 12 months of the year. (Remember, the ITCZ affects the tropical rain forest climate region throughout the year.) The dry season occurs when the ITCZ has moved away so that the convergence effects are not present. Yan- gon, Myanmar (formerly Rangoon, Burma), is an example of this climate type (Figure 10.4). Mountains prevent cold air masses from central Asia from moving over Yangon, re- sulting in its high average annual temperatures.
About 480 km north in another coastal city, Sittwe (Akyab), Myanmar, on the Bay of Bengal, annual precipi- tation rises to 515 cm, considerably higher than Yangon’s