贺兰山地区沙尘暴发生次数的变化趋势

Trend of Sandstorm Occurrence in Helan Mountain Area

通过统计分析贺兰山东、西两侧各 6个气象站的沙尘暴观测资料 ,结果表明 ,4月和 5月分别是贺兰山东、西两侧沙尘暴的高发期 ,盐池和拐子湖是东、西两侧的高发中心。沙尘暴发生日数的总趋势是减小的 ,但仍有 3个站沙尘暴发生日数有增加的趋势。

Sandstorm occurrence recorded by 12 weather stations by Helan Mountain was analyzed statistically. The maxium data length is 45 years. Monthly variation shows that April and May are the highest occurrence months in a year, its average occurring times is 3\^2 and 3\^1 respectively. Yanchi is the highest occurrence center at the east side of Helan Mountain area, where the maximum sandstorm occurring times is 5\^4 in April, Guaizi Lake is that at the west side with the maximum sandstorm occurring times of 5\^2 in May and the second of 5\^0 in April.\;Average annual variation suggests that the sandstorm occuring times is decreasing in general; this comes from afforestation and irrigating engineering. But annual variation showed by Yanchi, Guaizi Lake and Baiyan maodao stations appears a increasing trend, which results from deforestation, overgrazing or not effective desertification control.\;Although sandstorm occurrence times is decreasing generally in major Helan Mountain area, the strong and extra strong sandstorms come about increasingly. So the degree of hazard is more severe. The problem of that sandstorm is still the one of main meteorological hazards should not be taken lightly.