Climate and irrigation water use of a mountain oasis in northern Oman

The apparent sustainability of the millennia-old mountain oases of northern Oman has recently received considerable attention. However, little is known about crop growth and water use efficiency of these systems. To fill this gap of knowledge evapotranspiration and water use indices were modeled for nine field crops and date palm (Phoenix dactylifera L.) at Balad Seet, a typical oasis in the northern Omani Hajar range, whose agricultural area is composed of 8.8 ha of palm groves with 2690 date palms and 4.6 ha of land under field crops. Climatic data were derived from a weather station located in the oasis. The use of a digital elevation model (DEM) allowed estimating the shading effect of the surrounding mountains on evapotranspiration. When removing the site-specific effects of altitude and shading by surrounding mountains, reference evapotranspiration increased from 1778 mm year−1 to 2393 mm year−1. Total crop water requirements of the oasis were modeled at 194,190 m3 year−1 while measured available water resources from spring outflow and precipitation amounted to 245,668 m3 year−1. An irrigation water use efficiency of 0.75 at the oasis level provides evidence for an efficient use of this yield limiting resource in these ancient land use systems.