Forum Pakistan

This is one of the world's largest alluvial plains, embracing the valleys of the *Indus, the Ganges, and the Brahmaputra. It occupies the northern part of India and the greater part of Pakistan and Bangladesh. In the north-east it is bordered by the *Himalayas, in the north-west by the *Sulaiman Mountains, in the south by the Deccan tableland. It has the shape of an are, convex towards the north. It stretches about 3,000 km. from west to east and 250-300 km. from north to south. It was formed when the deep-pre-Himalayan 'cave-in' was filled up with sedimentary materials, brought down by in-flowing rivers and therefore the soils are predominantly of alluvial origin. The relief of the IndoGangetic Plain is characterised by gentle slopes, disrupted only by crystalline remnants of rocks in the west and the ledges of ancient alluvial terraces, marking the changes in location of the beds of the rivers. The mean slope is 17-20 cm./km. In watershed area , the slope is about 35 cm./km. and in the lowest-lying parts, 10 cm./km.

Climatically, the Indo-Gangetic Plain is divided into two parts. The western or *Indus Valley, primarily in Pakistan, is characterised by a dry tropical climate, the annual precipitation being 100-200 mm. The valleys of the Ganges and the Brahmaputra, in the eastern part, by contrast have a tropical monsoon climate. In both parts the mean air temperature is high. In the larger part of the plain the mean temperature for January is 15-20°C. In the eastern part, there is a summer season of heavy rainfall usually up to 90 per cent of the total annual precipitation. The south-western extremity of the plain is occupied by the *Thar Desert.

All three rivers and their tributaries have great seasonal fluctuations of their discharge. The waters of the rivers are extensively used for irrigation, without which agriculture is practically impossible in the valley of the Indus. The fertile alluvial soils of the IndoGangetic Plain are believed to have been the birthplace of ancient agricultural civilisation. The main crops cultivated in Pakistan are wheat, cotton, rice and millet.