Streamflow variability and its relationship with climate indices in western rivers of Argentina

The objective of this study was to examine the streamflow variability of Argentinean Andean basins (22°–52°S). Trends and step changes of seven hydrological variables were analysed. In addition, relationships between the hydrological variables and Pacific Decadal Oscillation (PDO), Niño 3.4, and Southern Annular Mode (SAM) indices were analysed. Most streamflow variables showed upward trends in the northwest and central-western basins, while downward trends were identified in the Patagonia (southwestern) region. Streamflow of the central-western and Patagonian basins was positively correlated with the Niño 3.4 index. Moreover, an inverse relationship with the SAM was found in watersheds south of 37°S. Positive step changes associated with the PDO phases in the north and central-western basins in the mid-1970s were detected, while negative step changes resulted in Patagonia between 1970 and 2000. This research provides new evidence of the influence of major climate modes on streamflow variability in the western rivers of Argentina.     

Plant community patterns in a gypsum area of NE Spain. II. Effects of ion washing on topographic distribution of vegetation

A model, based on the physico-chemical properties of gypsum, is postulated in order to interpret the regular distribution of plant communities associated with the topography and the main environmental stresses to which each vegetation type is subjected in a landscape unit.The leaf chemical composition of 28 representative plant species supports the main predictions of the model: species from low areas present large concentrations of Na, N and ash but low contents of Ca. It is demonstrated that the strong nutrient and salt downwashing in the hilly terrain is an important cause of the vegetation segregation observed on a large spatial scale.     

The Rotation of a Non-Rigid, Non-Symmetrical Earth II: Free Nutations and Dissipative Effects

The study of the rotation of a non-rigid, non-symmetrical Earth with a heterogeneous and stratified liquid core was recently accomplished by González and Getino (1997) through the Hamiltonian formalism. In this work that model is extended by including the effect of the dissipation arising from the mantle–core interaction due to the viscous and electromagnetic coupling. A canonical transformation to a new set of non-singular variables is performed, in order to avoid small divisors in the system of equations. Numerical estimations of the effect of the dissipation are given in form of tables and graphics, and the significance of this effect is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Well-balanced high-order centered schemes on unstructured meshes for shallow water equations with fixed and mobile bed

In this paper, we study the numerical approximation of the two-dimensional morphodynamic model governed by the shallow water equations and bed-load transport following a coupled solution strategy. The resulting system of governing equations contains non-conservative products and it is solved simultaneously within each time step. The numerical solution is obtained using a new high-order accurate centered scheme of the finite volume type on unstructured meshes, which is an extension of the one-dimensional PRICE-C scheme recently proposed in Canestrelli et al. (2009) [5]. The resulting first-order accurate centered method is then extended to high order of accuracy in space via a high order WENO reconstruction technique and in time via a local continuous space–time Galerkin predictor method. The scheme is applied to the shallow water equations and the well-balanced properties of the method are investigated. Finally, we apply the new scheme to different test cases with both fixed and movable bed. An attractive future of the proposed method is that it is particularly suitable for engineering applications since it allows practitioners to adopt the most suitable sediment transport formula which better fits the field data.