Abstract: Based on the data of 112 meteorological stations and 21 aerological stations in Northwest China from 1960 to 2009, the variation of 0 ℃ isotherm height and mean temperature in summer was analyzed. The result indicated that the mean height of 0 ℃ isotherm in summer was 4675.7 m during 1960-2009, with an annual decrease of 5.6 m before 1987 and an annual increase of 2.6 m after 1987. The ground temperature showed a similar annual trend at the 0 ℃ isotherm height, which was converse around the climatic mutation in Northwest China, with a considerable increase rate of 0.53 ℃ per decade after 1987. During 1960-2009, in most parts of Northwest China, the 0 ℃ isotherm height at Beijing Time 8:00 in summer increased significantly, and the height at Beijing Time 20:00 decreased. However, during 1987-2009, the 0 ℃ isotherm height in most parts of Northwest China increased at Beijing Time 8:00 and 20:00. A marked increasing trend of mean temperature in summer was observed in most parts of Northwest China, but the trend was opposite in Urumqi and Qinling-Daba Mountains. For the different climatic zones, the main trend and correlation between 0 ℃ isotherm height and mean temperature in summer varied spatially. The correlation was significant in the Cold Region on the Qinghai-Tibet Plateau, less significant in the Arid Region in Northwest China, and not significant in Monsoon Region in eastern China.

Key words: Northwest China, 0 ℃ isotherm height, mean temperature, climatic change