1957-2009年黄土高原地区风速变化趋势

用88个气象站1957-2009年的月平均风速和最大风速日值资料,采用距平累积法、 5 a趋势滑动法、 Mann-Kendall趋势检验法等分析了黄土高原地区风速的变化趋势及其空间分异等特征。结果表明:①黄土高原地区1957-2009年多年平均风速为2.36 m/s,水蚀区、 水蚀风蚀交错区和风蚀区年均风速分别为2.36、 2.17、 2.60 m/s,年际变化倾向率分别为-0.008 4、 -0.009 4和-0.018 8 m·s^-1·a^-1,并均通过了0.001的极显著性检验。3个区域均是冬、 春季的平均风速对全年趋势演变贡献率较大,年均风速也均在1981年发生偏强转为偏弱的跃变,20世纪70年代以后平均风速逐渐减小。②黄土高原平均风速减少的主要原因是最大风速为5级或5级以上的发生日数减少。大风频率从1970年代至2000年代呈显著减少趋势,风蚀区减少幅度最大,减少了10%以上,水蚀风蚀交错区减少1%~5%,到2000年代,大多数站点的大风频率均降低为<2%。③水蚀风蚀交错区和风蚀区年均大风日数较多,而水蚀区和黄土高原西部地区年均大风日数较少。根据大风年均发生日数,将大风天气划分为大风天气较少区(年均大风日数<10 d)、 较多区(10~50 d)、 多发区(50~100 d)和频发区(>100 d)。大风较多区在黄土高原地区分布最广,其次是较少区,无频发区。70年代至90年代,风蚀区和水蚀风蚀交错区的站点大多为大风较多区,其中70年代中宁和包头为大风多发区;2000年代以后,大部分地区转为大风较少区。

Spatial and Temporal Trends of Wind Speed on the Loess Plateau during 1957- 2009

An analysis of spatial and temporal trends of mean wind speed and maximum wind speed during 1957-2009 was performed on the Loess Plateau based on the monthly observed wind speed data at 88 meteorological stations. The cumulative departure analysis, a five-year moving average and the nonparametric methods of Mann-Kendall test, were used for data analysis. Results indicated that:
1) The annual mean wind speed(1957-2009)was 2.36 m/s on the Loess Plateau, annual mean wind speeds of water erosion region, wind-water erosion crisscross region and wind erosion region were respectively 2.36 m/s, 2.17 m/s and 2.60 m/s,and the mean wind speeds respectively decreased at the rate of -0.0084 m·s^-1·a^-1, -0.0094 m·s^-1·a^-1 and -0.0188 m·s^-1·a^-1,and respectively showed a significant decreasing trend (P<0.001). And on the seasonal scale, the contribution rates of spring and winter for annual wind speed were higher, summer and autumn were lower. For annual mean wind speeds in the three regions, the change point of the decreasing trend was in 1981, and after the 1970s, the wind speed decreased significantly.
2) The reason why the mean annual wind speed decreased significantly is that the decreasing of the frequency of the daily maximum wind speed with a scale ≥5. The frequency of the gale on the Loess Plateau showed a significant decreasing trend from the 1970s to the 2000s, the magnitude of decrease is the greatest in wind erosion region, by over 10%. By the 2000s, the frequency of gale in most stations on the Loess Plateau is <2%.
3) In most parts of wind-water erosion crisscross region and the wind erosion region, the number of gale days is more but it is less in the water erosion region and the east of the Loess Plateau. According to the annual mean frequency of gale days in the Loess Plateau, four sub-regions can be divided. They are fewer gale region (<10 d), more gale region (10-50 d), much more gale region (50-100 d) and frequent region (>100 d). Most parts of the Loess Plateau fall into the more gale region, and then fewer gale region and non-freguent region. From the 1970s to the 1990s, most parts of wind erosion region and wind-water erosion crisscross region belong to much more gale region. The Baotou and Zhongning stations belong to more gale region. After the year 2000, most parts of the Loess Plateau turn to the fewer gale region.