| The Loess Plateau in China is characterized with a vulnerable ecological system andsevere soil erosion in the world. Understanding the trend of wind speed and sandstorm iscritical for wind resources management and soil erosion control in this region. Daily data at88meteorological stations in and around the Loess Plateau from1957to2009were used toanalyze the spatial and temporal trend of mean wind speed, maximum wind speed and sandstorm,and the relationships between maximum wind speed and sandstorm. The cumulative departure analysis,a five year moving average and the nonparametric methods of Mann–Kendall test, were used for dataanalysis.The results showed that:(1)The annual mean wind speed(1957-2009) was2.36m/s on Loess Plateau, annualmean wind speeds of water erosion region, wind-water erosion crisscross region and winderosion region were respectively2.36m/s,2.17m/s,2.60m/s,and the mean wind speedsrespectively decreased at the rate of-0.0084m·s-1a-1,-0.0094m·s-1a-1å'Œ-0.0188m·s-1a-1,and respectively showed a significant decreasing trends(p<0.001). And on the seasonal scale,the contributions rate of spring and winter for annual wind speed were higher, summer andautumn were lower. For annual mean wind speeds in the three regions, the change point ofthe decreasing trend was in1981, and after1970s, the wind speed decreased significantly.(2)The reason why the mean annual wind speed decreased significantly is that thedecreasing of the frequency of the daily maximum wind speed stronger than the5grade. Thefrequency of the gale on Loess Plateau showed a significant decreasing trend from1970s to2000s, the most strong decreasing rate is in wind erosion region, which is larger than10%.By2000s, the frequency of gale in most stations on Loess Plateau is <2%.(3)In the most parts of wind-water erosion crisscross region and the wind erosion region,the gale weather is more than other regions. The gale weather is less in the water erosionregion and the east of the Loess Plateau. It can be divided into four sub-regions according tothe annual frequency of gale weather in Loess Plateau, which are fewer gale region(whereannual gale weather are less than10days),more gale region(where annual gale weather arebetween10to50days),much more gale region(where annual gale weather are between50to100days) and frequent region(where annual gale weather are more than100days).Mostparts of Loess Plateau are more gale regions, secondly, are fewer gale region. There aren'tany frequent regions on Loess Plateau. From1970s to1990s,the most parts of wind erosion region and wind-water erosion crisscross region are much more gale regions. The Baotouand Zhongning stations are more gale regions. After2000year, most parts of Loess Plateauturn to fewer gale region.(4) On Loess Plateau, the frequency and intensity of sandstorm is higher in the winderosion region, and is lower in the wind-water erosion crisscross region and is lowest inwater erosion region. The most stations of wind erosion region and wind-water erosioncrisscross region, sandstorms' with visibility <1.0km ratio>30%,while sandstorms' withvisibility <1.0km ratio<30%in the water erosion region.(5)The annual change of sandstorm weather on Loess Plateau showed a decreasingtrend, but only one station-Changwu in water erosion region showed a increasing trends.The significant decreasing trends in the wind erosion regions are higher than0.1d/a.(6)The frequency of sandstorm is not only affected by the distribution of gale days inLoess Plateau but also affected by the underlying surface. |
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