Land degradation cannot be judged independently of its spatial, temporal, economic, environmental and cultural context. Evaluations are therefore almost infinitely variable and very dynamic. These observations are examined in two contexts, first in two case studies. One, from the southern Levant, makes use of a long and well-documented history of environmental assessment that varied greatly between communities. The other, from contemporary Niger, shows finer scale differences among villagers. Second, the dynamic and multiple assessment of futures (sustainability) is illustrated with data from the same case study in Niger. In this wider context, multiplicity and dynamicity are largely a consequence of the choice of model of the environmental or social future. The usually positive difference between large-scale and finer scale assessments of degradation is dubbed the 'social delivery ratio'. Simplified systems of evaluation may be necessary for allocation, but they need to be treated with great caution if the argument here is accepted.
A mathematical formulation is developed to model the dynamics of sand dunes. The physical processes display strong non-linearity that has been taken into account in the model. When assessing the success of such a model in capturing physical features we monitor morphology, dune growth, dune migration and spatial patterns within a dune field. Following recent advances, the proposed model is based on a discrete lattice dynamics approach with new features taken into account which reflect physically observed mechanisms
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