The Sindh plain comprises mainly the province of Sindh and stretches between the Punjab plain and the arabian Sea. River Indus flows here as a single river and the plain comprises a vast fertile tract stretching westward from the narrow strip of flood plain on the right bank of River Indus, and a vast expanse of desert stretching eastward from the left bank. The desert area is dry and desolate like Cholistan in the Punjab plain. But, the plain area right of River Indus is green with a vast stretches of vegetation lined everywhere with avenues of trees. It is the heart of the Indus Valley Civilization dating back to 3rd millennium B.C. Thousands of tourists from all over the world are attracted every year to visit the ruins of Moenjodaro near Larkana. An elaborate canal system taken from Sukkur Barrage at Sukkur, Upper Sindh Barrage north of Sukkur at Guddu, and Lower Sindh Barrage (Ghulam Muhammad Barrage) at Hyderabad, irrigate together in this area over 10,000,0000 acres and account for about 40 per cent of Pakistan's irrigated land. The fertile area yields abundant crops of rice, wheat and cotton and contains the bulk of the population and most of the major commercial and industrial centres of Sindh such as Hyderabad(795,000), Sukkur (193,000), Larkana (123,000), Nawabshah (102,000), Shikarpur (88,000) and Dadu (39,000). However, its southern part is one of the worst areas of Pakistan for waterlogging and salinity. There are many lakes in Sindh,which attract thousands of migratory birds during the winter season from Central Asia. Manchhar lake with its highly pulsating expanse of about 200 sq.miles of area is the largest lake. With its foliage of towering grasses, its meadows of floating lotus, its inhabitants in their floating habitations, the lake presents an attractive look. Further south, stretches the Indus Delta, which is a savage waste. An important feature is the Kinjhar Lake near Thatta, which acts as a great reservoir for feeding canals in the adjacent areas. During winter, it is an ideal spot for fishing and duck shooting. South of the Kinjhar Lake, the surface is broken and littered with abandoned channels of distributaries, sandy beaches, ridges and mangrove swamps, all merging into the dead creeks, grate and salt water of the coast of Rann of Kutch. At the extreme north-western end of the delta stands Karachi, the largest city and the industrial and commercial hub of Pakistan. It is also the port for Pakistan and terminal of Pakistan's railway system and the site of the country's principal international airport. Climate and Seasons As Pakistan is located on a great landmass north of Tropic of Cancer, between latitudes 24 and 37 N, it has a continental type of climate, characterized by extreme variations of temperature. The areas closer to the snow-covered northern mountains are cold. Temperatures on the Balochistan Plateau are comparatively high. Along the coastal strop, the climate is modified by sea breezes. In the rest of the country, temperature rises steeply in the summer and hot winds, called "loo", blow across the plains during the day, dust storms and thunder storms occasionally lower the temperature. The diurnal variation in temperature may be as much as 11 to 17 oC. Winters are cold with minimum temperature of about 4 oC in January. Rainfall Pakistan experiences a general deficiency of rainfall.