Abstract
Turpan is an oasis in the arid land of Northwest China. It is generally considered that agriculture would be impossible in arid lands without the oases, which contribute to the improvement of the meteorological conditions. To identify the characteristics of the velocity and direction of the wind in Turpan, and the effect of tree windbreaks on the improvement of the meteorological conditions in this oasis, investigations were carried out from August 27 to September 12, 1997. The prevailing directions of wind with a velocity of more than 5 m/s were W and WSW. The stronger wind in Turpan was attributed to an inflow of cold air mass after the passage of a depression. The effect on the improvement of the meteorological conditions varied considerably depending on the arrangement of the tree windbreaks. In an area of the oasis with strong windbreaks 1 km distant from the desert, where trees were arranged at intervals of more than 10 trees /10 m and the tree height exceeded 10 m, the air temperature decreased by about 5°C and the relative humidity increased by 14% compared with the outside desert. Air temperature and relative humidity were constant in any area of the oasis 1 km apart from the desert. In another oasis area with weak windbreaks, in which trees were arranged at intervals of less than 10 trees /10 m and the tree height was less than 10 m, the effect of the windbreaks on the improvement of the meteorological conditions was negligible.
