关键词: 极端气温, 榆林地区, 极端气温突变, 周期

Abstract: Using the daily temperature data of weather station of Hengshan, Yulin and Suide from 1954 to 2013, adopting the linear fitting, accumulative anomaly, Morlet complex wavelet analysis, we calculated and analyzed ten kinds of extreme temperature indices released by WMO. Results indicated that the extreme maximum temperature and extreme minimum temperature in Yulin in last 60 years have a escalating trend, but the ice day, frost day, cold night, cold day number decreased, and summer day, hot night, warm night, warm day present steady rising trend. In the past 60 years, the change of extreme temperature in Yulin had obvious change characteristics in phase and the mutation phenomenon. The mutations of the extreme temperature and cold and warm indices mainly occurred in 1990s. The variation of warm indices is the main reason why the temperature of Yulin rose in the last 60 years. The increasing of temperature in spring and winter is the main reason that annual average temperature rose. The 33a cycle is a relatively stable one for the ten kinds of indices in Yulin. Warm extremes and annual temperature range would keep rising while cold extremes would decrease. In the study area, increasing of the extreme high temperature days would have enhance chance of extreme weather such as drought, and will have a pressure on prevention of forest fires. Reducing of extreme low temperature days prone to forest and grassland pests and diseases.

Key words: extreme temperature, Yulin, abrupt change of extreme temperature, period