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Accueil du site → Doctorat → Espagne → 2004 → Developing a desertification indicator system for a small Mediterranean catchment : a case study from the Serra de Rodes, Alt Empordà, Catalunya, NE Spain

Universitat de Girona (2004)

Developing a desertification indicator system for a small Mediterranean catchment : a case study from the Serra de Rodes, Alt Empordà, Catalunya, NE Spain

Dunjó Denti, Gemma

Titre : Developing a desertification indicator system for a small Mediterranean catchment : a case study from the Serra de Rodes, Alt Empordà, Catalunya, NE Spain

Auteur : Dunjó Denti, Gemma

Université de soutenance : Universitat de Girona

Grade : Doctor of Philosophy (PhD) 2004

Résumé
The aim of this research was to develop a simple methodology for precisely appraising the status and trends of desertification in a semi-arid Mediterranean catchment, through a so-called desertification indicator system (DIS). The assessment of land degradation processes at plot scale was conducted through the monitoring of runoff-erosion microplots. As a result, a set of variables such as soil erosion, soil organic matter and vegetation cover, were identified as the most important factors for soil quality in the target area, and some of these were applied as inputs in the DIS model, accounting for their relevance not only at the plot but also at catchment scale. Regarding the parameter sensitivity of the DIS model, the saturated hydraulic conductivity as well as the erodability factor were identified as the most sensitive variables, whereas the soil-b parameter and also the vegetation cover and the slope angle were revealed as those affecting soil erosion and overland flow the least. Likewise, the model showed greater sensitivity to the dry than to the normal or wet rainfall scenarios. From the results of a plot scale model validation exercise it may be concluded that the behaviour of runoff and erosion at plot scale is somewhat different to that at the landscape scale : a scaling problem. At the plot scale, soil erosion was greatly overestimated by the model in the least vegetated environments and especially under cultivated olive trees, whilst it was slightly underestimated in the most vegetated ones (e.g. dense cork trees). The same pattern was found for overland flow, although measured and modelled runoff data were in the same order of magnitude and so errors were smaller than for erosion. Nevertheless, results may be considered significant in terms of which land uses are the most and least potentially degraded and in this way, the model fulfils its objective as a desertification support tool as it identifies the patterns of change expected, if not the magnitudes. The model would need to be more complex, have better and more input data and a regional scale validation if the magnitudes were to be predicted reliably. Since soil loss is considered the main indicator of soil erosion processes, according to FAO/UNEP/UNESCO (1979), the original landscape as well as the two developed scenarios, one related to a hypothetical landscape after a wildfire and another to a completely cultivated landscape, may be classified as being under low to moderate land degradation. In comparison to the original scenario, both developed scenarios were revealed to have higher soil erosion and runoff rates, especially the cultivated scenario. Hence, these two scenarios seem not to be a sustainable alternative to land degradation processes in the study area. However, a wide range of alternative scenarios may be developed with the DIS model, based on policies of particular relevance to the region and which help to determine the potential desertification consequences of these policies in this spatially complex landscape

Mots Clés : Desertificación – GIS — Mediterranean area— Àrea mediterrànea — Canvi d’ús del sòl — Serra de Rodes — Parc Natural del Parc de Creus — Cambios de usos del suelo — Land-use change — Land abandonment — Model numerico-espaial — Spatio-numerical modeling — Abandonamiento de tierras – Desertification — Abandonament de terres — Desertificació

Présentation (Tesis Doctorals en Xarxa)

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