SE A ST 1 - (Week 1) A Physical Environment

SE A ST 1 - (Week 1) A Physical Environment - ments in...

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Unformatted text preview: ments in Southeast Asia, ranging from the volcanic peaks of Indonesia and mangrove shorelines ofViet— nam to the virgin forests of the highlands of Burma. This natural diversity has had an enormous impact on the rela- tionship between society and nature in the region. The in- tent of this overview is to provide a broad outline of the physical environment of the region and to demonstrate why it is of crucial importance to an understanding of con- temporary patterns of diversity and development. Knowl- edge about the physical environment is essential to a better understanding of both patterns and processes of social, po- litical, economic, and environmental change in Southeast Asia. The first half of this chapter will provide an overview of the region’s physical geography and its natural resources, and the second half will utilize this information to inform discussions regarding present-day environmental issues in the region.A true understanding of current environmental change is possible only with knowledge of the human so- cieties and physical environment in which they exist.The re— lationship between society and the environment is key. There is a remarkable diversity of physical environ- LANDFORMS The region is conventionally divided into two major zones: peninsular and insular, or island, Southeast Asia. Peninsular Southeast Asia consiSts of the mainland coun- tries of Burma, Cambodia, Laos, Thailand, and Vietnam, and insular Southeast Asia is comprised of Brunei, In- donesia, Malaysian Borneo (Sarawak and Sabah), the Philippines, and Singapore. Although peninsular Malaysia is physically part of the mainland, it is usually considered part of the insular region because culturally and histori- cally it is more closely related to this area.The total land area of peninsular and insular Southeast Asia is approx- imately equal; however, they represent very different ge~ ological histories. Peninsular Southeast Asia, the entire island of Bor- neo, and the floor of the intervening South China Sea (the Sunda shelf) are all part of the Eurasian tectonic plate. The Philippine and Indonesian archipelagoes, on the other hand, are on the margin where the northeast- 6 moving Australian plate and the west—moving Philippine and Pacific plates are colliding with the Eurasian plate. Because the Philippine, Pacific, and Australian plates are oceanic plates and therefore heavier than the continental Eurasian plate, they are being forced down into the Earth’s crust. These areas where continental plates are overriding oceanic plates are called subduction zones and are characterized by a series of deep-sea trenches off- shore that coincide approximately with the boundaries of the various plates. In fact, they almost completely en- circle Southeast Asia (Map 2.1). It is in the vicinity of such subduction zones that mountain-building activities including earthquakes and volcanic activity takes place. Indeed, the Indonesian and Philippine archipelagoes have been created as a result of the collision of these tectonic plates and are, respectively, the first- and second-largest archipelagoes in the world in terms of the number of is- lands they contain; Indonesia is made up of about 13,000 islands and the Philippines has more than 7,000 islands. Southeast ASia is one of the most conspicuous areas of seismic (earthquake) activity in the world. In fact, “Be- cause of the high population density, more people are subjected to some degree of earthquake risk in South- east Asia than anywhere else in the world. Over 200 mil- lion people live in an area in which there is at least one great earthquake every decade, a large earthquake every year, and perhaps a thousand small earthquakes, some of which cause damage, every year” (Arnold, 1986, p.15). Indonesia alone claims approximately 22 percent of the world’s active volcanoes. The onshore counterpart to the oceanic trenches is a series of mountain ranges that parallel the subduction zones. As a result of this tectonic activity, the Philippines and Indonesia are home to a large number of dormant and active volcanoes as well as a great deal of earthquake activity. Both nations are part of the “Rim of Fire” that surrounds the Pacific Ocean. TWO of the largest volcanic eruptions in the nineteenth century occurred in Indone- sia,Tambora in 1815 and on tiny Krakatau Island in 1883. Effects are often devastating; in the case of Krakatau the 2,640-ft (800~m) peak of the volcano collapsed to 1,000 ft (300 m) below sea level, leaving only a small portion of The Physical Environment '7 Subduction Zones AUSTRALIAN |_ Selected Active Land Volcanoes Present Areas of Folding and Faulting [Approximate Plate Boundaries} PHILIPPINE PACIFIC PLATE Map 2.1 Structure zones and features. Source: Ulack and Porter; 1989, p. 4. the island standing above sea level. Ash from the erup- tion colored sunsets around the world for two years and gate rise to the “Chelsea sunset” paintings in England. In addition, a tsunami (tidal wave) was generated that killed 36,000 people in nearby Java and Sumatra. The largest volcanic eruption in the twentieth century oc- curred on the island of Luzon in the Philippines at Mt. Pinatubo in 1991. While the explosion of Mt. Pinatubo resulted in fewer than 200 deaths, it displaced well over a 100,000 people and destroyed tens of thousands of hectares of productive agricultural land. Moreover, the la- hars (a rapid flow of water, mud, and volcanic debris) that occur during the rainy season will continue for years to come. At the same time, the long~tern1 effect of volcanic ac- tivity in both Indonesia and the Philippines has general- ly been to produce soils that, by tropical standards, are relatively fertile. This results from the fact that most of the volcanic material in the area is basic rather than acidic in composition. The soils that have evolved from this 8 Chapter 2 nonacidic volcanic material can support sustained levels of agricultural activity. The high population densities on Java are, in part, at least a function of the fertile volcanic soils. However, it is important to remember that, because of its relatively high population density when compared to other seisniically active regions, more people in South- east Asia are at risk from volcanoes and earthquakes than in any other major world region. Because the insular portion of the region is geologi- cally younger, in general, than the peninsular region, the relief of island Southeast Asia tends to be more severe; that is, it is characterized by steeper slopes and higher el- evations. Generally, there are very few large areas of lit- tle or no relief in the entire region.The largest areas of relatively flat land are found in river valleys and the larg- er deltas of the Irrawaddy, Chao Phraya, Mekong, and Red Rivers; the only exceptions to this are the larger in- land basins of Burma, Thailand, and Cambodia. As a topographic map reveals, much of Southeast Asia may be characterized as having mountainous or hilly terrain. The settlement pattern of Southeast Asia has been dominated by densely populated river valleys or deltas separated by hilly, forested areas with very low popula- tion densities. These intervening upland forest areas have acted as barriers between the more heavily populated set- tlement clusters. Over time, successive immigrant groups have settled in the lowland coastal, valley, and delta areas of the region. However, as more recent and more-populous groups have come into the region, they have “pushed” ear- lier, less-sophisticated groups into upland areas, thereby bringing about divisions and conflicts between upland, or “hill,” peoples, and lowland groups. Today, the lowland areas are populated by the dominant ethnic group of each Photo 2.1 A volcanic landscape in west Java. (Leinbach) country including the Burmese in Burma, Thais in Thai- land, Khiners in Cambodia, and Javanese in Java. 0n the other hand, the upland, forested areas are populated by ethnic minority groups, for example, the Shans in Burma, and the Yao and Miao in Thailand.As a result of the very different environments that lowland and upland peoples have inhabited for thousands of years, very different liveli- hood systems have evolved. In general, uplanders have engaged in some form of dry field or shifting cultivation known as swidden, and lowlanders have practiced inten- sive wet rice cultivation, or sawah.'Ihese general patterns continue today and are important for understanding sev- eral critical environmental issues in the region. Most of the coastal plains in Southeast Asia are rela- tively narrow. There are only two significant exceptions to this statement: the deltas of the major rivers, such as the Irrawaddy and the Mekong, and the eastern coast of Sumatra and the southern coast of Borneo. Both of these coastal areas, however, are occupied by swamps and are not suitable for large-scale agriculture and dense settle- ment. In short, due to the narrowness of its coastal plains and its generally hilly to mountainous terrain, Southeast Asia overall has had a relative shortage of cultivable land. For example, land under crops or in pasture comprises only 7 percent of the total land area of Laos, 15 percent in Malaysia, 16 percent in Burma, and 21 percent in Cam- bodia and Vietnam. This is to be contrasted with the Unit— ed States where almost 50 percent of all land is under some form of agriculture. The long-term adaptation to this situation involved the evolution of numerous forms of land—extensive shifting cultivation, and labor-intensive agriculture (particularly irrigated rice but also including backyard gardens and the growing of crops on terraces). The geology of Southeast Asia is remarkably complex and is the result of hundreds of millions of years of rift- ing and subsequent colliding of landmasses This process continues today. In a very general sense, Southeast Asia is composed of three geologic regions, and insular South- east Asia is the result of the collision of the various ocean- ic plates with the Eurasian plate. Peninsular Southeast Asia, on the other hand, is composed of two geologic units: a central core located primarily in Cambodia, east- ern Thailand, and southern Vietnam, and a mountainous region that surrounds this low lying core. This moun- tainous area includes northern Burma and Thailand, Laos, and most of Vietnam and is the result of more-recent uplift. The mountainous and semimountainous terrain and the island nature of many of the countries of the region combine to create One of the distinctive characteristics of the area as a whole—its fragmented nature. This in turn has led to considerable diversity with regard to adap— tation to the natural environment. It has also contributed to great socioeconomic and cultural diversity in the re» gion. Indeed, it is quite appropriate that this fragmented region was labeled by geographers a “shatterbelt” and the “Balkans of the Orient” (Brock, 1944; Fisher, 1962). By way of summary, an appreciation of the geomor— phology of the region is important because it highlights features of the area that are helpful in trying to under- stand past and ongoing events. First, the remarkable phys— ical geographic variability has resulted in an equally remarkable variation in land use and cultural practices. This diversity is one of the distinguishing characteristics of Southeast Asia. Second, the relative lack of flat, easi- ly tilled agricultural land continues to have an effect on the types of agriculture that can be practiced. Lowland agriculture, particularly irrigated rice has, in general, been very labor intensive. Terraced agriculture (primarily for irrigated rice) is also found throughout the region. Clas- sic examples are the rice terraces of northern Luzon, the Philippines, and the island of Bali in Indonesia. It remains to be seen whether or not these adaptations to the natural environment can provide useful examples of sustain- ability for contemporary society. In particular, as popu- lations continue to increase and expand into hilly and mountainous areas, a major question is whether or not more-intensive agricultural systems can be devised to work in upland areas without, at the same time, causing excessive environmental damage. CLIMATE Nearly the entire Southeast Asian region can be said to be part of the humid tropics; that is, the region is warm all year round and receives abundant but temporally and spatially uneven rainfall (Map 2.2). Overall, the annual average temperature is approximately 80°F (27°C), and The Physical Environment 9 seasonal variation in temperature is usually less than the diurnal variation; that is, the difference between daytime and nighttime temperatures is greater than the differ- ence in temperatures between the winter and summer months. In addition to latitudinal position, temperature is also a function of altitude as it decreases with increasing ele- vation. This decrease, referred to as the environmental lapse rate, is equal to about 3°F per 1,000 ft increase in el- evation. The result is that because the region as a whole is so hilly or mountainous, almost all nations in South- east Asia have areas of higher elevations where cooler temperatures prevail. It is at higher elevations that hill stations emerged during the colonial period; today, these hill stati0ns are often referred to as upland resorts. In the Philippines, for example, one of the first things the U.S. personnel did following the defeat of the Filipinos after the Spanish-American War was to develop the city of Baguio in northern Luzon as a retreat to escape the heat and humidity of summertime Manila. The area around Baguio is now a major producer of temperate fruits and vegetables for the Philippine domestic market and is a popular tourist destination. Other examples of such hill stations include Dalat in southern Vietnam, the Cameron Highlands in peninsular Malaysia, and the Karo High- lands of North Sumatra. Some of these hill stations— Bandung on Java is the best example—have become major metropolitan areas (Photo 2.2). Although it is difficult to provide an average rainfall figure because there is so much variation within the re- gion, a figure of 80 in. (200 cm) per year would be con- sidered normal in many areas At the same time, however, a distinction must be made between equatorial and trop- ical, or monsoon, rainfall regimes. Equatorial areas are on or near the equator, from about 10 degrees north to 10 degrees south of the equator. Equatorial regions re- ceive rainfall throughout the year; that is, they do not have a dry period. Singapore is a good example of an area in which rainfall is evenly distributed throughout the year (Figure 2.1). Tr0pical monsoon climate regions generally affect areas more than 10 degrees north and south of the equator, and such areas are characterized as having distinct wet and dry seasons Manila and Rangoon are good examples of weather stations that are charac- terized by monsoon conditions (Figure 2.1). In turn, this seasonal variation in rainfall is largely a function of the monsoons, winds (and their accompanying rains) that al- ternate direction on a regular basis (Map 2.2). The term monsoon is derived from the Arabic word mausin, which refers to the time of the year the wind occurs and which made possible the seasonal trips across the Indian Ocean. These winds are caused by the seasonal migration of high- and low-pressure areas, which, in turn, are caused by the differential heating of land and water, movement of the subtropical jet stream, and other factors. During 10 Chapter 2 Wfii \ TROPICAL MONS N “Y 4-...“ H - U dryr months 1—4 dry months 5-8 dryr months 9-12 dry months h...— January monsoon 4--------.. Julymonsoon Map 2.2 Climate Patterns: Prevailing winds and length of dry season. Source: Mack and Patter; 1989, p. 6. the winter months, the monsoon winds blow from the northeast off the Asian landmass, and during the sum- mer months they originate from the southwest off the In- dian Ocean. Equatorial regions receive both monsoons and, hence, are wet all year; tropical areas, on the other hand, usually receive only one monsoon a year and, hence, have a dry period at some point during the year, sometimes as long as six months. It is important to rec- ognize that although monsoons are the dominant factor in seasonal variations of rainfall, the rainfall pattern in Southeast Asia is the result of a variety of complex and interlinked forces Other factors that are important in- clude cyclonic disturbances, localized land—sea breezes, and the presence of mountains. The western Pacific Ocean is the origin of a severe tropical weather disturbance called a typhoon (called a hurricane in North America and a cyclone in south Asia). These weather systems primarily effect the northern two- thirds of the Philippines but may also reach parts of peninsular Southeast Asia, particularly Vietnam. They are accompanied by high winds and heavy rainfall. In fact, until recently, the world record for precipitation in a 24-hour period was held by the city of Baguio in the Philippines, where in 1911 46 in. (117 cm) of rain fell dur- ing a typhoon, or baguio. On Occasion, tropical thunder- storms can match the intensity of typhoons. In 1991, the Orinoc region of Leyte, the Philippines, was hit with such a storm; it is estimated that almost 16 in. (40 cm) of rain- fall occurred in a 4- to 6-hour period. In the massive flooding that followed, approximately 6,000 people were killed. Tropical rains tend to be more intense than temperate rains; that is, the amount that falls in any given time pe- riod is greater. Because erosion is, to a certain extent, a function of the amount and intensity of rainfall, this nec- essarily means that tropical regions like Southeast Asia are more vulnerable to erosion than temperate regions This is particularly the case in steeply sloped upland areas The problem is compounded if planting results in the removal of much of the original ground cover. In short, the hilly topography and intense rainfall mean that many upland areas in the region are environmentally fragile. This point is of direct relevance to any discussion regarding future uses of the upland areas in Southeast Asia, especially for agriculture. Another important factor that has an effect on rain— fall is the presence of mountains. Air masses are forced to rise over mountain barriers because they cool and their ability to hold moisture declines, resulting in rainfall called The Physical Environment 11 Photo 2.2 Guest house in Fraser’s Hill, Pahang, Malaysia, a hill station. (Leinbach) orographic precipitation. This means that the windward side of a mountain range usually has a significantly greater amount of rainfall than the leeward, or “rain-shadow,” side. The effect of mountain ranges on local precipitation is a function of the length and height of the mountains, the prevailing winds, and the absence or presence of mon- soons. Examples of areas that experience orographic pre- cipitation include almost the entire western coast of Sumatra, the northeast and northwest coasts of Luzon, and coastal Burma. Good examples of the rain-shadow effect include the island of Cebu in the central Philippines and the “dry zone” of central Burma. Both of these areas receive less rainfall because of higher elevations in sur- rounding areas. On a smaller geographic scale, the pres- ence of mountains means that there can be much local variation in rainfall, which may influence the type of agri- culture practiced. The length of the dry period is a crucial factor con- trolling the natural vegetation in an area and the type of agriculture that is possible. If we define a dry month as one that receives less than 4 in. (10 cm), then most of peninsular Southeast Asia has an average dry season of approximately 5 months. Many islands in eastern In- donesia, such as Flores and Timor, also have dry periods of at least 5 months. ...
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