According to the census of the year 2000, the total population in Tibet was 2.62 million. With diversity in terms of distribution, most people live in rural areas, and fewer in cities and towns. The population of the Tibetan nationality accounts for over 90% of the population, but that of the Han nationality and other ethnic groups is very small. Affected by nature, geographic conditions and climate, 80% of the population in Tibet is distributed mainly over the valley along the middle reaches of the Brahmaputra River valley and the deep valleys along three rivers ( Lantsang River , Lujang River and Yangtse River ) which are located in the eastern part of Tibet . There are few people in the northern part of the Qinghai-Xizang Plateau because of its harsh climate. The southeastern part of Tibet is covered by primeval forests; there population density is low, transportation is inadequate and other conditions unfavorable.