G. del Barrio

Topographic controls on the spatial distribution of ground cover in the Tabernas badlands of SE Spain

Abstract The relationships between the spatial distribution of ground-cover and terrain attributes were examined in the Tabernas badlands (SE Spain) in order to understand the terrain-dependent driving forces of the spatially heterogeneous ground cover. Ground cover was mapped in the field and terrain attributes were derived from a 1-m resolution Digital Elevation Model (DEM). The association of spatial distribution of the landforms resulting from a regionalisation (using a nonhierarchical classification of the topographic overlays) and the ground-cover pattern was proved. From the analysis of relationships between terrain attributes and proportional abundance of ground-cover types, it was found that ground cover is arranged along topographic gradients: plant-covered surfaces are more abundant on low slope angles, concave slopes, relatively large contributing areas and with low length slope factor values. Unvegetated surfaces show contrary trends and lichens are associated with intermediate conditions. Relationships with local terrain attributes, such as slope angle or elevation, are more pronounced than those with terrain attributes related to sediment and water transfer, such as contributing area, wetness index or length slope factor which could be explained by the heterogeneity of runoff that is usually shorter than the hillslope length. The relationships established between the spatial distribution of ground-cover types and terrain attributes provide the basis for future development of a tool for mapping spatial distribution of ground cover in similar areas from only topographic information.

Assessment of rainfall and NDVI anomalies in Spain (1989-1999) using distributed lag models

In this study a link was established between anomalies in climatic and Advanced Very High Resolution Radiometer (AVHRR)/Normalized Difference Vegetation Index (NDVI) data in Spain for the period from 1989 to 1999 on a monthly and annual basis using multivariate distributed lag (DL) models and generalized least‐square (GLS) parameter estimation. In most areas significant time‐delayed correlation between anomalies of monthly rainfall and NDVI data was confined to an interval of 1 month. Locally higher lag orders of up to 3 months were found. By contrast, relationships between surface temperature and the NDVI were insignificant in the multivariate context at most locations. The multiple correlation coefficients of the DL models achieved 0.6 in the maximum. Regions characterized by the most significant NDVI–rainfall correlations include the southern forelands of the Pyrenees in Catalũna, rainfed agricultural areas in Extremadura, Andalusia, and the western parts of Castilla y Leon. Average ratios of rainfall to potential evapotranspiration (PET) in the sensitive areas ranged between 0.5 and 2, with annual rainfall amounts less than 700 mm. For each land‐cover class a linear discriminant analysis (LDA) was carried out to assess the environmental factors that might explain the differences in the NDVI–rainfall relationships. The highest discriminant coefficients and factor loadings were recorded for those factors that recurrently trigger water deficit in the sensitive regions, such as low total annual rainfall, large seasonal rainfall variability, high average PET and surface temperature. On the annual basis the lagged correlation of the NDVI and rainfall data was confined to natural vegetation (grassland and scrubland) areas in western Spain. This region suffered from a severe drought in the early 1990s, after which biomass production lagged several years behind improved rainfall conditions. The approach presented is useful for assessing the influence of climatic variables on the pattern of temporal anomalies in the NDVI or related vegetation parameters.

Sediment transport in a high mountain catchment in the central Spanish Pyrenees

Abstract This paper reports on sediment transport rates from a 0.33 km2 high mountain catchment in the central Spanish Pyrenees. Sediment transport from three distinct periods are compared: winter, when discharge is very low and regular; the spring snowmelt season, when discharge is high during several weeks, with daily oscillations; and the rest of the year when discharge is controlled by fluctuations in the precipitation regime. It is shown that sediment transport is dominated by the summer and autumn storm events, with the storms of October 1987 accounting for 61% of the bedload transport in seven years. In addition the sediment transport is considered in three components: solutes, suspended sediment load and bedload. In years with a normal pluviometric regime, the ratio between the three modes of sediment transport is between 82 and 94 percent solutes, 5 to 7.5 percent suspended sediments and 1 to 10 per cent bedload. This too varies greatly from year to year, with the October 1987 storms transporting 17 tons of bedload transport whilst the dissolved and suspended load only reached 2,000 and 750 kg respectively.

Monitoring desertification using EO technologies: Experience of the ESA DUE DesertWatch project

The DesertWatch ESA DUE project, recently successfully completed, aimed at developing an integrated information system tailored on the specific user needs, built on the technological transfer of the most significant results of the related research projects. The resulting DesertWatch Information System, a user-friendly integrated Software remote sensing tool for monitoring desertification, have being installed and is now used in Italy, Turkey and Portugal.