Effects of land use changes on the hydrological sustainability of mountain oases in northern Oman

Abstract

Traditionally, oasis farmers in hyperarid northern Oman have adapted to the interannual variation of irrigation water supply by dedicating an often sizable proportion of the agricultural area to the production of annual crops and leaving this area uncultivated in drought years. We hypothesized that increases in the share of perennial crops may put long-term hydrological sustainability at risk. To test this hypothesis, we compared agricultural water demand patterns of five oases in the mountain region of Al Jabal al Akhdar for 1978 and 2005. We analyzed land use changes by classifying aerial photographs taken in 2005 and 1978 into five land use types. Water demand in 2005 was estimated based on two GIS-based detailed crop inventories during the hot and cool season and on measurements of temperature, solar radiation and wind speed, from which crop evapotranspiration was calculated using the Penman-Monteith equation. Radiation and wind speed measurements were improved by topographic modeling. Water demand per area was summarized for each land use type and the results used to estimate water demand in 1978. Water supply estimates were based on spring flow measurements. Between 1978 and 2005, agricultural water demand in the study area rose from 218,800 to 256,377 m 3 a −1 . The most prominent land use changes were the disappearance of non-palm orchards at Masayrat ar Ruwajah and expansions of the area under perennial crops at Al 'Aqr, Ash Sharayjah and Qasha' at the expense of field crops. As a consequence, the summer peak of crop water demand decreased at Masayrat ar Ruwajah, where all perennial crops could easily be irrigated with the minimum water supply observed during our study, but this summer peak increased at the other oases. Meeting the water demand of all perennial crops at Qasha' required average spring flow conditions in 2005, indicating severe water deficiency in drought years. In addition to increased water demand, the oases' water balance might also be under pressure from reductions in water supply caused by increased extraction of water from the same aquifer by a rapidly growing new town in the area.

Climate change effects on winter chill for tree crops with chilling requirements on the Arabian Peninsula

“…Since the software also required measurements of solar radiation, we added such data recorded at the town of Sayh Qatanah, about 2 km from the weather station, between (Luedeling and Buerkert 2008a. For all three scenarios, we generated 100 years of daily weather data.…”

Adjusting homestead feeding to requirements and nutrient intake of grazing goats on semi-arid, subtropical highland pastures

“…Farmers in the oases of Al Jabal al Akhdar traditionally cultivate green fodder in their gardens and produce about 0.5 kg OM/m 2 of fodder per harvest (Dickhoefer, unpublished). Since the fodder is harvested six to eight weeks after seeding and is directly re-sown (Luedeling and Buerkert, 2008), about 25 to 35 m 2 of fodder area would be needed to feed a goat of 35 kg BW at 21 g OM/kg 0.75 BW per day on a year-round basis, which is equivalent to the green fodder intake of R2 goats (see section 'Feed intake'). In April 2006, alfalfa, maize, barley, oat and sorghum cultivation in the oasis gardens on Al Jabal al Akhdar covered an area of 2000 to 7600 m 2 per village (Luedeling and Buerkert, 2008).…”

Modelling chemical and biological reactions during unsaturated flow in silty arable soils

“…Predominant rock types are amongst others limestone, dolomite and diamictite. Qasha' is characterized by subtropical, hyperarid climate conditions with a mean annual temperature of 20.8°C and very low mean annual precipitation (b100 mm) (Luedeling and Buerkert, 2008). The site is used for irrigation agriculture; the dominant soil type is Irragric Anthrosol (FAO, 2006).…”

“…The main cultivated plants are maize, barley, oat, garlic and sweet potato. Twenty-five percent of the area are covered by trees such as pomegranate or peach (Luedeling and Buerkert, 2008).…”