Abstract: Based on the mean minimum temperature data of seven meteorological stations in 1971-2007 in Tianshui during the half year of winter,which was from November to April of the next year,the abrupt changes of the minimum temperature were analyzed by using Mann-Kendall statistic test.The probability distributions of the minimum temperature series for the colder periods in 1971-1972 and 1995-1996 and warmer periods in 1996-1997 and 2006-2007 were analyzed.The differences of the spatial distribution of the minimum temperature between the two climatic periods were also compared.The results showed the significant increase of the minimum temperature occurred in the middle of 1990's.Its increasing amplitude was larger than that of the mean temperature.The partial cold probability of the minimum temperature apparently reduced,while the partial warm probability of the minimum temperature increased.The minimum temperature in the North of the Wei River and the valley of Wei River significantly increased with exception in the Guan Mountain Areas.

Key words: Half year of winter, Half year of winter, Minimum temperature, Probability distribution, Tianshui