Wind Regimes Windward of a Shelterbelt Protecting Gravity Irrigated Crop Land from Moving Sand in the Gezira Scheme (Sudan)

Summary  The work reported on was part of a more comprehensive study dealing with threatening sand movement towards the northwestern part of the Gezira irrigation scheme, Sudan. An irrigated sand blocking shelterbelt Eucalyptus microtheca is used to prevent canals and gravity irrigated crop land to be further affected. The objective of this paper is to report on the wind data that were obtained, mainly windward of this belt, and to deal with their implications and those of the belt characteristics and deposited sand in interaction with the wind for combating local sand movements and further desertification. Outside the influence of the belt, wind speed over eroded land was increasingly higher than that over irrigated land with the growth of cotton. Both these values were considerably higher than those reported from the nearest meteorological stations. The two prevailing winds, of which the summer SW wind was perpendicular to the belt, had consistent annual patterns during three years of observation. Also the diurnal patterns were very reproducible. Wind speed within the belt, at 1 m height, showed fast reduction inwards above the deposited sand. Efforts to control moving sand in the source area should be joined with those made at the borders of agricultural land. Received August 20, 1997 Revised September 30, 1998