Geological environment and causes for desertification in arid-semiarid regions in China

. In the past 40 years, the desertification rates have reached between 0.81 and 1.64% per year in northern China. Many researchers have focused their studies particularly on climate change and human activities occurring in recent years but have overlooked the possible effect of changing geological environment on a much longer time scale on this deterioration of land. Using the Geologic Information System (GIS) technique, the impact of climate change, eolian deposit, loess formation, and the Quaternary environment in the past 20,000 years on desertification during three periods of dry-cold, warm-humid and dry-cold conditions was investigated. The results indicate that the important factor causing the drought and desertification in the north is the uplifting of the Qinghai-Xizang Plateau in the past 10,000 years. The time scale on which natural factors contribute to desertification is 1,000?10,000 years, whereas that of human influence is only in the magnitude of a decade to about 100 years. There is evidence to indicate that the change in the Quaternary geological environment was the decisive factor for the desertification. The destruction of vegetation and surface soil cover is the direct and immediate cause leading to the present desertification. In the past 50 years, the climate in northern China has been predominantly dry and warm, creating a favorable condition for the desertification process. Therefore, it is an important task for China in the 21st century to protect vegetation and to limit land development so as to stop the desertification process.