Sustainability of mountain oases in Oman

Traditional oasis systems in northern Oman are rapidly being changed by various transformation processes affecting these ancient settlements. The first objective of this dissertation was to estimate the number of oases in northern Oman and to characterize them according to their topographic, hydrologic and geologic settings. The number of oases was determined based on an analysis of Landsat ETM+ images, from which the Normalized Difference Vegetation Index (NDVI) was calculated. As a preparatory step for the analysis of oasis settings, the so-far best elevation model of northern Oman, which was derived from data from NASA’s Shuttle Radar Topography Mission (SRTM), was improved by filling gaps in the dataset using topographic information from Russian military maps. The resulting elevation surface and geological survey data were then used to classify the oases detected on the Landsat images into six types: Plain Oases, Foothill Oases, Mountain Oases, Urban Oases, Kawr Oases and Drainage Oases. Since the arid conditions in Oman make the presence of a reliable source of irrigation water one of the prime prerequisites for agricultural production, the stability of the water supply was examined for a selection of six oases in the Oman Mountains. This analysis was based on spring flow measurements and determination of water retention times in geological storage formations. The results imply that the water supply of oases in the foothills is generally more stable than that of mountain oases. The final two studies focused on some of the highest agricultural oases in Oman, which lie in the region of Al Jabal al Akhdar. Farmers in this region cultivate fruit trees typically found in temperate and cool subtropical areas at an altitude of up to 2000 m a. s. l. An analysis of past and present climatic conditions indicated that the number of chilling hours, which is a determining factor for a site’s ability to produce good yields of such crops, declined sharply over the past two decades, apparently threatening these traditional cropping systems. Finally, land use changes over the past 27 years have altered the water demand patterns of these oases. Increases in the area planted with perennial crops at the expense of annuals made some oases more vulnerable to droughts, because perennial orchards cannot easily be left uncultivated, when the water supply drops below average conditions.