عواصف الغبار في المناطق الصحراوية في الأردن: منطقة القطرانة – ضبعة: حالة دراسية

Dust storms in the desert areas of Jordan: the Qatraneh-Dabaa region: a case study

The present research aims at addressing the impacts of surface conditions and meteorological forcings in affecting the development of dust storms in the Jordan Badia. A strip of land extending from the Qatrana (31° 12' N; 36° 08' E) to Dhabba (31° 34' N; 35° 39' E) along the Amman – Aqaba highway was chosen to carry out this research. Thirty-four soil samples taken throughout the study area from the top 2-5 cm of the soil layer at the end of September/ early October, 2009 were used to investigate soil particle size distribution, soil moisture and soil texture. A thorough scrutiny of surface conditions (vegetative cover and state) and the level of surface disturbance (extent and intensity of anthropogenic activity, presence or absence of consolidated crust) was carried out to establish surface erodibility. Particle size, which was classified using a sieving method, indicates that the surface soil is sandy, with the dominant size fraction being in the coarse range. Field survey and lab measurements confirm that the study area had been subject to extensive and severe degradation, which is manifested by soil size distribution and total removal of vegetation cover. Surface conditions along with the prevailing meteorological conditions intensify the severity and frequency of dust storms in the study area. Daily and 6- hourly wind speed and visibility extracted from meteorological data collected at Qatrana meteorological station during the period 2000 – 2009 were analyzed. It was shown that the maximum wind speed blows primarily from two distinct directions, south and west. Surface particle size distribution was used to establish the threshold surface friction velocity. A preliminary assessment of dust storms forming in the study area is presented. Based on wind speed data, the probability of dust/ sand storms forming in the study area is around 9% of days in the year ( ≈ 32 days). This figure is larger than the corresponding data reported by the operating meteorological station in the study area. Data compiled by the Department of Meteorology/ Jordan concerning dust storm frequency and intensity suffer from two serious shortcomings; they are discrete in nature and point measurements. Such data can be used as indicators of dust storm events rather than to be used as representative and real values, per se. Field measurements and thorough surface inspection indicate clearly that the tragedy of the commons is nakedly distinct in this environment, as manifested by almost the total removal of vegetation cover, severe and cyclic disturbance of the surface, and complete absence of environmental regulations. Keywords: Aeolian Erosion, Dust Storms, Threshold Friction Velocity, Jordan Desert, Tragedy of the Commons, Consolidated Crusted Surface, Soil Texture.