THE CHANGING TREND OF SAND AND WIND ACTIVITIES IN BEIJING
He Dalang (Institute of Desert Research,Academia sinica,Lanzhou)
There was a ohvious decrease of sand and wind activities during the last tne years in beijing. The average windy days and the sand-driving wind days from 1991 to 1992 were 34% and 21. 9% respectively as compared with the multi-year average values before 1980. The reason of decrease of sand-driving wind days was that the sand producted in Beijing area itself decreased because of a better- green-layer above land . But if the greening-work in the upper-reach of wind area delays, it will have aimpact on the sand and wind activities in Beijing.