Tibet is a land of scant rainfall and a short growing season, and the only extensive agricultural region is the Yarlung Zangbo valley, where barley, wheat, potatoes, millet, and turnips are grown. In this valley as well are nearly all the large cities, including Lhasa , Xigazê (Shigatse), and Gyangzê (Gyangtse). Most other areas of Tibet are suited only for grazing; yaks, which can withstand the intense cold, are the principal domestic animals, and there are also large herds of goats and sheep. Much of the population is engaged in a pastoral life, but the advances made by irrigation and the growing of forage crops is decreasing the amount of nomadism, and Chinese attempts to spur economic development have also increased the urban population. In addition to vast salt reserves, Tibet has large deposits of gold, copper, and radioactive ores.