近50a宁夏初、终霜日基本特征及变化趋势

Characteristics and Change Trend of the First and the Last Frost Dates in Ningxia in Recent 50 Years

利用1961—2010年宁夏20个气象站的逐日最低气温资料,根据霜冻气候指标统计了初霜日和终霜日,采用基础统计和气候诊断分析方法,研究了宁夏全区及不同区域的初、终霜日基本特征和变化趋势。结果表明:近50 a宁夏平均初霜日在10月上旬、终霜日在5月上旬,其中引黄灌区的初霜日最晚、中部干旱带次之、南部山区最早,而终霜日的排序正好相反;全区平均初霜日呈推后趋势、终霜日呈提前趋势,3个区域初、终霜日的年际变化趋势均与全区一致,只是倾向率略有不同;年代际变化上,在20世纪60、70年代,全区平均初霜日偏早、终霜日偏迟,80年代以后,表现为初霜日偏迟或接近平均、终霜日偏早或接近平均,3个区域的初、终霜日年代际变化与全区相似;全区及3个区域的初霜日均在1974年发生突变;而终霜日的突变年有所不同,宁夏全区、中部干旱带和南部山区均为1983年,引黄灌区为1982年。

Based on the daily minimum temperature data at 20 meteorological stations in Ningxia from 1961 to 2010, the first and the last frost dates were counted according to the frost indexes and statistics. Using statistical and climate diagnosis methods, the characteristics and change trend of the first and the last frost dates were analyzed. The results showed that the average first frost date came in early October while the average last frost date appeared in early May next year in Ningxia over the recent 50 years. However, it was not equal in the whole region. The earliest first frost date appeared in the mountain areas in the south, the next was in the dry areas in the middle and the latest first frost date appeared in the Yellow River irrigation area in the north. The last frost dates were sorted contrary with the first frost dates in the above three regions. In general, the average first frost date appeared late while the average last frost date came early in Ningxia in the last 50 years. The trend changes in the three regions showed no difference with the trend in the whole region. In 1960s and 1970s, the first frost dates were earlier and the last frost dates were later than the averages of the last 50 years. Since 1980s, the first frost dates were later or close to the average but the last frost dates were earlier or close to the average. The first frost date cumulative departures abruptly changed in 1974 for the whole region but the last frost date cumulative departures were changed in different years in the three regions which was in 1983 for the middle dry areas and the south mountain areas and was in 1982 for the Yellow River irrigation are-