西北地区近50a气温和降水极端事件的变化特征

采用1960-2009年西北地区124个气象站点的逐日最高气温、最低气温和日降水量资料,对该地区极端气候变化进行了研究探讨,并在此基础上尝试预测了未来该地区极端气候变化的情形。研究表明:近50 a以来,西北地区夏季天数、生物生长季、热夜天数、高温天数分别以2.31、2.98、1.07、0.45 d·(10 a)^-1的速度显著增加;结冰天数、最大连续霜冻天数、低温天数分别以-2.51、-1.79、-3.62 d·(10 a)^-1的趋势在显著减少;极端气温年较差也以-0.39℃·(10 a)^-1的速度在减少;除极端气温年较差外,极端温度指数和年平均气温有很好的相关性;最大的1和5天降水总量、逐年平均降水强度和持续干旱天数呈增加趋势,而中雨天数和持续降水天数呈减少趋势;除持续干旱天数外,年降水总量与其他极端降水指标有很好的相关;从空间分布和各气候区来看,极端气候增加或减少的趋势及其与年平均气温或年总降水量相关性不尽相同。

The Change in Extreme Events of Temperature and Precipitation over Northwest China in Recent 50 Years

Based on daily temperature(maximum and minimum)and daily precipitation at 124 meteorological stations over Northwest China observed by the China Meteorological Administration during the 1960-2009 period, the variability of extreme events of temperature and precipitation over Northwest China in recent 50 years is analyzed and its extreme climatic variation in future is predicted. Eight indices of extreme temperature and six of extreme precipitation are studied. Over the 1960-2009 period, the occurrence of summer days, growing season length, hot night days and maximum temperature days have significantly increased by 2.31, 2.98, 1.07 and 0.45 days/decade, respectively. Over the same period, the regionally averaged occurrence of extreme ice days, consecutive frost days and minimum temperature days have significantly decreased by -2.51,-1.79 and -3.62 days/decade, respectively. The annual temperature range also exhibits a decreasing trend (-0.39℃/decade). With the exception of diurnal temperature range, the other indices correlate with annual mean temperature very well. Precipitation indices about annual maximum with 1-day and 5-day precipitation, consecutive dry days and averaged daily rainfall intensity have no statistically significant increasing trends while the number of heavy precipitation days and consecutive wet days decrease. At the same time, there are significant correlations between annual total precipitation and precipitation extremes except consecutive dry days. In spite of the above-mentioned main trends and correlations in most parts, the differences in spatial distribution and different climatic regions still exist significantly.