Based on the ECMWF's first atmospheric reanalysis data of the 20th Century

ERA-20C

the variation of the boundary-layer height (BLH) and its relationship with the meteorological factors over arid and semiarid areas of East Asia and North Africa spanning 1900-2010 were analyzed. The BLHs in the two areas showed an opposite trend in the overall

interannual and interdecadal variation. The BLH of East Asia overall showed a rising trend with a climate tendency rate of 1.87 m/10a

while the BLH of North Africa showed a decreasing trend with a climate tendency rate of -2.13 m/10a. In the 11 decades

there were 8 decades having opposite trend. The BLH was related to the change of land air temperature gradient

relative humidity and wind speed. The change of relative humidity had a good correlation with the BLH

with significant negative correlation coefficients of -0.778 4 and -0.618 4

respectively

in East Asia and North Africa.