Abstract:For comparing wind velocity field and windbreak effects between the one-line-one-belt (OLOB) and two-lines-one-belt (TLOB) schemes of sand-break forests, we studied horizontal and vertical profiles of wind velocity field of the two schemes at 20% and 25% cover under simulated wind speeds of 10 and 15 m/s. It was found that in both schemes there was a complex horizontal flow field comprising wind shadows and acceleration areas. The two schemes showed similar effects on the vertical profile of wind speed. We divided the vertical space into three layers according to the different effects on vertical wind speeds: the layer with slight change (20 to 35 cm above the ground), the layer with significant change (6 to 12 cm above the ground), and the layer with steady change (0.4 to 3cm above the ground). For each of the layers, the two schemes displayed the same pattern of variation. The TLOB was less effective in reducing horizontal wind speed than the OLOB before the first belt, but the former was more effective after the first belt. The observed patterns of reduced vertical wind speed were such that wind speed was reduced at 0.4 to 50cm above the ground, with the reduction being more apparent at 0.4 to 12cm, and that the TLOB was more effective in reducing wind speed near ground surface (0.4cm) than the OLOB.