Surface energy and water vapor fluxes observed in a desert plantation in central Iran

Summertime observations of surface radiation budget, energy balance and atmospheric surface layer meteorology were made on an arid valley floor planted with Haloxylon aphyllum to combat desertification in central Iran. The surface microclimate is characterized and compared with other arid regions and the role of ‘desert greening’ on surface fluxes is considered. A high surface albedo (0.265) and large longwave radiation loss produced relatively low net radiation. Energy partitioning was dominated by sensible and ground heat fluxes with opposing diurnal asymmetry governed by strong diurnal variability in eddy diffusivity. The Bowen ratio was 2.53, which fell inside the range of other vegetated arid surfaces. Surface temperature gradients were strong both in the atmospheric surface layer and in the substrate, with consistent lapse conditions by day and inversions at night. The wind regime included a moderate daytime regional wind which displayed Coriolis turning and weaker nocturnal slope flows. Actual evapotranspiration (1 mm dy⁻¹) was only a small fraction of potential evapotranspiration. The diurnal pattern of AET indicates strong stomatal control. The desert greening effect of Haloxylon plantations provided atmospheric water and reduced sensible heat flux by up to 40%.