1. In the first step, three large regions are divided to reflect the combined effectof hydrothermal conditions. In the northwest, the water insuficiency hampers thefunction of warmth; in the Tibetan Plateau, the low temperature hinders the fullutility of water; it is only in the monsoon area, where precipitation occurs in thewarm period, does the water-heat combination yield better results. These three regionsare of order 1.