The application of remote sensing data to diagnose soil degradation in the Dakhla depression – Western Desert,Egypt

Dakhla depression in Egypt’s Western Desert is experiencing two soil degradation processes, notably: soil salinization and sand encroachment. The present study aimed to diagnose the severity of these processes using remote sensing. Soil salinity was determined by spectral regression analysis between tasselled cap spectral transform extracted from a Landsat-8 image acquired in September 2013 along with synchronized soil salinity measurements. Assessment of sand advance rate was conducted by temporal change detection of brilliant crescentic sand dune visualized by Google Earth in old (2002) and recent (2013) images. Results showed that salinized soils (dS/m4<) represent 91% of bare lands and salinization is attributed to aridity, topography and poor drainage. Barchan dunes north and south of Abu Tartur escarpment moved at rates of 5.9 and 3.6 m/year, respectively. The escarpment protected the majority of the depression from massive dune invasion. However, sand encroachment is clearly observed west of the depression.     

Spatiotemporal drought variability in northwestern Africa over the last nine centuries

Changes in precipitation patterns and the frequency and duration of drought are likely to be the feature of anthropogenic climate change that will have the most direct and most immediate consequences for human populations. The latest generation of state-of-the-art climate models project future widespread drying in the subtropics. Here, we reconstruct spatially-complete gridded Palmer drought severity index values back to A.D. 1179 over Morocco, Algeria, and Tunisia. The reconstructions provide long-term context for northwest African hydroclimatology, revealing large-scale regional droughts prior to the sixteenth century, as well as more heterogeneous patterns in sixteenth, eighteenth, and twentieth century. Over the most recent decades a shift toward dry conditions over the region is observed, which is consistent with general circulation model projections of greenhouse gas forced enhanced regional subtropical drought.     

Expansion theory for the elliptic motion of arbitrary eccentricity and semi-major axis

In this paper of the series, elliptic expansions in terms of the sectorial variables θ _j ⁽ⁱ⁾ introduced in Paper IV (Sharaf, 1982) to regularise highly oscillating perturbation force of some orbital systems will be explored for the first four categories. For each of the elliptic expansions belonging to a category, literal analytical expressions for the coefficients of its trigonometric series representation are established. Moreover, some recurrence formulae satisfied by these coefficients are also established to facilitate their computations, numerical results are included to provide test examples for constructing computational algorithms.     

Membership in the open cluster NGC 2301

Astrometric cluster membership probabilities have been derived from proper motion of the open cluster NGC 2301. A comparison with previous investigations is presented.     

Dynamics of the long-period tides

The long-period tides are a tool for understanding oceanic motions at low frequencies and large scales. Here we review observations and theory of the fortnightly, monthly and pole tide constitutents. Observations have been plagued by low signal-to-noise ratios and theory by the complex lateral geometry and great sensitivity to bottom slopes. A new spectral element model is used to compute the oceanic response to tidal forcing at 2-week and monthly periods. The general response is that of a heavily damped (Q ≈ 5) system with both the energy input from the moon and the dissipation strongly localized in space. The high dissipation result is probably generally applicable to all low frequency barotropic oceanic motions. Over much of the ocean, the response has both the character of a large-scale and a superposed Rossby wave-like character, thus vindicating two apparently conflicting earlier interpretations. To the extent that free waves are excited they are consistent with their being dominated by Rossby and topographic Rossby wave components, although gravity modes are also necessarily excited to some degree. In general, a modal representation is not very helpful. The most active regions are the Southern Ocean and the western and northern North Atlantic. These results are stable to changes in geometry, topography, and tide period. On a global average basis, the dynamical response of Mm is closer to equilibrium than is Mf.     

The influence of physical and biological processes on the ichthyoplankton communities in the Gulf of Sirte (Southern Mediterranean Sea)

This paper reports on the first study on the ichthyoplankton community structure in the Gulf of Sirte and its spatial distribution in relation to environmental conditions and zooplankton abundance. The results make an important contribution to the future management of fisheries in this unexplored, but much exploited, area. Biological samples were collected in July 2008 using a Bongo40 net. In total, 1914 larvae were found and 1652 of these were identified. In particular, bathypelagic taxa were the most abundant, followed by demersal, mesopelagic, pelagic and epipelagic taxa. The ichthyoplankton community had a patchwork distribution influenced by oligotrophic conditions, the bottom depth and oceanographical features. The results suggest that environmental forcings were able to transport the ichthyoplankton to productive areas. Indeed, maximum fish egg densities were found in coastal stations in correspondence with the Atlantic Tunisian Current inflow, whereas larvae were mainly concentrated in the east side of the Gulf, probably as a result of advection by the anticyclonic circulation. Additionally, the distribution patterns of the total larvae density and the different assemblages were well matched with the abundance of the zooplankton, probably determining final larval survival, growth and recruitment.     

Drought assessment in a south Mediterranean transboundary catchment

ABSTRACT

Predicting the impacts of climate change on water resources remains a challenging task and requires a good understanding of the dynamics of the forcing terms in the past. In this study, the variability of precipitation and drought patterns is studied over the Mediterranean catchment of the Medjerda in Tunisia based on an observed rainfall dataset collected at 41 raingauges during the period 1973–2012. The standardized precipitation index and the aridity index were used to characterize drought variability. Multivariate and geostatistical techniques were further employed to identify the spatial variability of annual rainfall. The results show that the Medjerda is marked by a significant spatio-temporal variability of drought, with varying extreme wet and dry events. Four regions with distinct rainfall regimes are identified by utilizing the K-means cluster analysis. A principal component analysis identifies the variables that are responsible for the relationships between precipitation and drought variability.     

Seismic microzonation for Muscat region,Sultanate of Oman

Natural Hazards - Site characterization was carried out for Muscat region using the ambient noise measurements applying the horizontal-to-vertical spectral ratio (HVSR) technique and using active...     

Condition of development of collapse structure in the southern–central Atlassic Tunisia case study to Gafsa Basin

The Bou Omrane is an example of southern–central Atlassic Tunisian folds, this massive is presented by an anticline delimited by a NE–SW thrust. The geometry study of this anticline (hinge and subvertical layers) associated to structural and stratigraphic correlation confirms the development of structures according to “fault propagation fold” model. Using numerical software Rampe 1.3.0, the balanced cross-sections demonstrate the complicated growth of Bou Omrane anticline. The resulted structure is obtained by thrusting on breakthrough coupled to blockage of ramp on the back limb. All these condition confirm the role of diversity of tectonics events and the inheritance tectonics notion associated with the reactivation of pre-existing faults on the genesis of folds and the development of collapse structures according to more than one decollement level.