Deriving drainage networks and catchment boundaries: a new methodology combining digital elevation data and environmental characteristics

In Mediterranean regions there is little experience in using GIS as an aid to land evaluation. This paper reports a project in Greece which investigated the usefulness of such technology, Particular emphasis was also given to comparing the results of land evaluation using Boolean and fuzzy set methodologies. The need was to produce the results as quickly and efficiently as possible to aid agricultural planning. By using a GIS, a series of single factor and land evaluation maps was produced for a range of crops; a land suitability map for receipt of sewage was also derived. A comparison of results from using Boolean and fuzzy set methodologies highlighted the advantages of the latter, although critical decisions are required on choice of membership functions and weights which have a major effect on the results.

A land evaluation project in Greece using GIS and based on Boolean and fuzzy set methodologies

In this article, an extensive inventory in the literature of water erosion modelling from a geospatial point of view is conducted. Concepts of scale, spatiality and complexity are explored and clarified in a theoretical background. Use of Geographic Information Systems (GIS) is pointed out as facilitating data mixing and model rescaling and thus increasing complexity in data-method relations. Spatial scale, temporal scale and spatial methodologies are addressed as the most determining geospatial properties underlying water erosion modelling. Setting these properties as classification criteria, 82 water erosion models are identified and classified into eight categories. As a result, a complete overview of water erosion models becomes available in a single table. The biggest share of the models is found in the category of the mechanistic pathway-type event-based models for watershed to landscape scales. In parallel, geospatial innovations that could be considered as milestones in water erosion modelling are...

A classification of water erosion models according to their geospatial characteristics

Many spatially distributed environmental models have been developed for small spatial units (e.g. individual plots or fields). Their application at a regional scale (e.g. large drainage basins) was hitherto not very successful since most models are ‘scale-specific’. In most cases the lack of input data is a limiting factor for an appropriate model application at a regional scale. The use of simplified models on the other hand, can only be successful if they have the appropriate degree of complexity. This leads to the following paradox: on the one hand a model should be based on process knowledge so that it will react correctly to changes imposed by the modelling system. Including all available process knowledge, however, will lead to an overparametrisation. The error propagation involved in the poor data quality can then deteriorate dramatically the accuracy of the output results. For optimal model predictions at a regional scale the model complexity has to be in balance with the quality of the available ...

Data quality and model complexity for regional scale soil erosion prediction

Soil loss on arable agricultural land is typically an order of magnitude higher than under undisturbed native vegetation. Although there have been several recent attempts to quantify these accelerated fluxes at the regional, continental and even global scale, all of these studies have focused on erosion by water and wind and no large scale assessment of the magnitude of tillage erosion has been made, despite growing recognition of its significance on agricultural land. Previous field scale simulations of tillage erosion severity have relied on use of high resolution topographic data to derive the measures of slope curvature needed to estimate tillage erosion rates. Here we present a method to derive the required measures of slope curvature from low resolution, but large scale, databases and use high resolution topographical datasets for several study areas in the UK to evaluate the reliability of the approach. On the basis of a tillage model and land-use databases, we estimate the mean gross tillage erosion rates for the part of Europe covered by the CORINE database (6.5% of global cropland) and we obtained an average of 3.3 Mg ha(-1) y(-1), which corresponds to a sediment flux of 0.35 Pg y(-1). Water erosion rates derived for the same area are of a similar magnitude. This redistribution of soil within agricultural fields substantially accelerates soil profile truncation and sediment burial in specific landscape positions and has a strong impact on medium-term soil profile evolution. it is, therefore, clear that tillage erosion must be accounted for in regional assessments of sediment fluxes and in analyses that employ these in the analysis of land management strategies and biogeochemical cycles. Copyright (C) 2009 John Wiley & Sons, Ltd.

E.Menezes de Sequeira

Papers

The methodological approach to soil erosion and important land resources evaluation of the European community