CHANGE IN DUST STORM FREQUENCY AND THE CLIMATIC CONTROLS IN NORTHERN CHINA

Duststorm is one of serious environmental problems in northern China.Based on the surface observation data,tendency of days with duststorm and the relationship between annual and seasonal days with dust storm and the climatic factors,such as wind,relative hum idity,air temperature,precipitation and dry ness index,were analy zed.The results show that days with duststorm had been fluctuant decreasing during 1954-2001,especially in spring.Climatic factors in dust resource areas obviously affect the occurrence and development of duststorm.Relationship analysis shows that wind is a key factor to the occurrence of dust storm in the study area.Bothaverage wind speed and days with strong wind are import ant for development of duststorm.Negative correlation between air temperature and days with dust storm was also found,indicating that a warming north will lead to a decrease in days with dust storm.Increase of precipitation over the source areas of dust during the past 50 years or so mighthave restrained the development of duststorm.The precipitation in winter such as snow,will melt in spring,and will be useful supply to wet the earth surface in the next spring.So the total precipitation in spring and the previous winter is much more important.Relative humidity generally plays a similar role with precipitation.Dryness index,which incorporates the effect of precipitation and temperature,was correlated as well with duststorm frequency,and it was found to be a good indicat or for occurrence of dust weather phenomenon.