The evaluation of the amount of water requirement for afforestation, range improvement and forage production particularly in arid regions is considered as one of the essential needs of the executive departments in the country. In this article, the water requirement for Haloxylon was determined in three desert areas of Iran (Ahwaz, Bandarabbas, Chahbahar) using Cropwat 8-FAO Penman-Mnteith method. For this purpose, climate data were obtained from the nearest station to the plantation areas of

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... oxylon. Soil texture, depth of root zone and other properties were evaluated from soil profile analysis where plant species were investigated. The phenology of the species was prepared through the available references and studies. After collecting all required metrological data, effective precipitation was derived from USDA method. Reference evapotranspiration (ETo) of each station and the amount of effective precipitation were then calculated at study areas for each individual stations. Results showed that effective rainfall in desert areas had a small contribution to plant water requirements, thus supplementary irrigation is needed during the growth season. This study also showed that the highest water deficiency for Haloxylon was recorded in July, June and May. It is also concluded that the annual reference evapotranspiration and the amount of effective precipitation in Ahwaz, Bandarabbas, and Chahbahar were calculated to be 2044, 1825, 1642 mm; 108, 93 and 59 mm, respectively. The highest annual-water requirement estimated by Crop-wat for Haloxylon species in above three stations was calculated to be 211, 112 and 77 mm, respectively. It also showed that although the three regions were located in areas with similar climatic and vegetative regions, the amount of water needed for supplementary irrigation in Ahvaz was almost three times higher than that in Chabahar and two times higher than that in Bandar Abbass.