The Physical Environment Topography

The Himalaya and its associated mountain ranges form a physical and cultural divide between South Asia and the lands to the north and east. They rise in a series of roughly parallel ranges northward from the plains of Bangladesh, India, and Nepal, with each range progressively higher. The much lower Sulaiman and Kirthar ranges of western Pakistan, with their many passes, have permitted intercourse with other parts of Asia. Mountains closest to the plains have been heavily denuded of their forest cover, and are subject to intense soil erosion.

South of the world's highest mountain system is the densely populated alluvial plain of Ganga in India and Bangladesh, and the Indus Plain, mostly in Pakistan. Both these plains have extensively developed systems of irrigation. Canal irrigation is particularly well developed in the Indus Plain and the western Ganga Plain. These plains are subject to periodic flooding that is especially heavy and periodically devastating in the eastern part of India and Bangladesh.

The Thar Desert, south of the Indus Plain, is shared by India and Pakistan. Here is a vast arid region hemmed in from the east by the low Aravalli Range. This thinly populated desert region is characterized by shifting sand dunes, large playa lakes, salt pans, and, to the southwest, marshlands.

South of the Ganga Plain is peninsular India. Composed of several plateaus, this region, except for the black soils of the Deccan Plateau and the river deltas, is primarily an area of thin, reddish soils of medium to poor quality. Part of the peninsula that is still forested and of marginal quality for agriculture is home to many tribal people. Skirting the peninsula on the west is the narrow but intensively cultivated and densely populated Malabar coast. On the east the coastal plain is broader. The island nation of Sri Lanka is composed of central highlands surrounded by a coastal plain.

Climate

South Asia is very hot during the summer; the highest temperatures are found in the Thar Desert. Hot desiccating winds in May and June are frequent in the entire Indus—Ganga Plain and cause substantial problems of heat stress (Planalp 1971). Temperatures of over 90°F are commonplace. In the mountainous regions elevation modifies the temperatures. During winter there is a general temperature gradient from north to south. Temperatures are in the 40°F range in the north, reaching well over 75°F in the south.

South Asia is characterized by a high degree of rainfall seasonality, with very uneven geographic distribution, and great variability from year to year. In much of India, Bangladesh, Nepal, Bhutan, and Pakistan, most of the rainfall is received from June through September. Over the southern part of peninsular India, autumn rainfall is significant. On the southeastern coastal area the predominant season of rains is autumn.'Most of peninsular India and the Thar region suffer from high variability of rainfall. In general, the seasonality of rainfall in the predominantly agrarian societies of South Asia has meant that farming is very dependent upon rainfall despite major developments in irrigation during the twentieth century. Variability of rainfall, therefore, means that farming communities may suffer from frequent seasonal food shortages, undernutrition, lowered resistance, and higher morbidity.

Convincing arguments have been made about the relationship of climatic seasonality to seasonal morbidity, especially among the poor. Evidence from diverse regions of the world, including India/and Bangladesh, shows that seasonal fluctuations bear more heavily on the poor than on other social groups (Chambers, Longhurst, and Pacey 1981). High-rainfall regions, especially where humidity is also high (e.g., the Malabar coast, Eastern India, and Bangladesh) are the major endemic areas of infectious diseases such as cholera, typhoid, filariasis, and malaria.

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