Gabriel del Barrio

Differential responses of hillslope and channel elements to rainfall events in a semi-arid area

The degree of hydrological connectivity of hillslope elements in a semi-arid climate was studied at the season and event timescales. Field data were obtained in Rambla Honda, a Medalus project field site situated in SE Spain, on micaschist bedrock and with 300 mm annual rainfall. The season timescale was assessed using correlation analysis between soil moisture and topographic indices. The event timescale was studied by a quasi-continuous monitoring of rainfall, soil moisture, runoff and piezometric levels. Results show that widespread transfers of water along the hillslope are unusual because potential conditions for producing overland flow or throughflow are spatially discontinuous and extremely short-lived. During extreme events, runoff coefficients may be locally high (ca. 40% on slope lengths of 10 m), but decrease dramatically at the hillslope scale (<10% on slope lengths of 50 m). Two mechanisms of overland flow generation have been identified: infiltration excess, and local subsurface saturation from upper layers. The former occurs during the initial stages of the event while the latter, which is quantitatively more important, takes place later and requires a certain time structure of rainfall intensities that allow saturation of the topsoil and the subsequent production of runoff. Hillslopes and alluvial fans function as runoff sources and sinks respectively. Permanent aquifers are lacking in Rambla Honda. Variable proportions of hillslope areas may contribute to flash floods in the main channel, but their contribution to the formation of saturated layers within the sediment fill is very limited.

Response of high mountain landscape to topographic variables: Central pyrenees

An objective method for inductively modelling the distribution of mountain land units using GIS managed topographic variables is presented. The landscape of a small high mountain catchment in the Spanish Pyrenees, covered with grassland, was classified in ten land units by hierarchical agglomerative clustering, using a sample of 194 random plots, in which classes of vegetation, soils and landforms were defined. Additionally, seven layers of topographic variables (altitude, slope angle, aspect, solar radiation, topographic wetness index, specific catchment area, and regolith thickness) were created from a Digital Elevation Model. The affinity of each land unit to the topographic variables was calculated using Binary Discriminant Analysis (BDA), after dichotomising the latter around their mean values. Then, the distribution of each land unit was predicted by boolean operations combining step by step distributions for the seven topographic variables ordered, for each unit, after the absolute values of the Haberman’s residuals in BDA. The predicted distributions were tested (χ2) against that of the observed sampling plots. From the original ten land units, the distributions of eight of them were successfully predicted (four are related to the slope sequence, two reflect the water accumulation in the soil, and two respond to geomorphic processes) while the remaining two had to be rejected. Part of the catchment (39%) was not assigned to any land unit, probably because more distributed variables accounting for snow distribution are necessary.

Mapping soil depth classes in dry Mediterranean areas using terrain attributes derived from a digital elevation model

Abstract Modern land management increasingly demands quantitative information on spatially variable soil properties. Traditional soil survey maps do not provide this information. In this paper we report on the application of terrain attributes to mapping soil depth classes at high spatial resolution over large areas under dry Mediterranean conditions. Soil data were collected in 111 georeferenced field plots of 30 m × 30 m, more or less equally distributed over three lithological units, phyllites, shales and limestones. Topographic attributes were computed from a digital elevation model at 30 m resolution. A principal components analysis was carried out on the map overlays of the terrain attributes in order to obtain uncorrelated topographic factors that enabled us to apply a probability approach. Using the maximum likelihood classifier with the field plots as a dispersed training area, predictions were made of mean soil depth class and the probability of occurrence of shallow or deep soils. A cross-validation revealed a 65%, 81% and 61% accuracy for the three maps of the shale area, a 50%, 55% and 40% for the maps of the phyllite area, and a 78%, 72% and 75% accuracy for the maps of the limestone area. Explanations for both the good results in the shale and limestone areas, and the poor results in the phyllite area, focus on the effects of the spatial scale of topographic variation, sediment transport mechanisms, and the impact of land use.

Computer simulation of high mountain terracettes as interaction between vegetation growth and sediment movement

Terracettes are common features on steep slopes between 1700 and 2700 m a.s.l. in the central Pyrenees. These microforms can be understood as the result of the interaction between the growth of bunch grass (Festuca eskia) and geomorphic processes; the first element provides a discontinuity of the physical properties of the slope, and the second element modifies the growing pattern and affords the characteristic microprofile of the slope. In order to analyse the former relationship, assuming that the sediment transport is only caused by a surface process, a computer simulation experiment has been performed. The first purpose of this model is the construction and verification of a set of hypotheses, and the production of a guide for field investigations. This model may then be used to investigate several questions concerning the geoecology of these features such as the role of geomorphic processes and vegetation behaviour, whether they represent a steady-state or an aggradation or degradation succession, and their efficiency as soil stabilisation features. The first results, obtained during sensitivity analysis, show that it is easy to simulate the formation and evolution of individual forms although the biological model parameters for the generation of a continuous trend of terracettes are rather narrow, due to the risk of demographic instabilities or explosions. Once a parameter set is achieved, simulated terracettes are self reproducing in a dynamic equilibrium condition. Simulated sediment transfer is lowered when a good terracette pattern is obtained, as a consequence not only of the vegetation cover but also of the topographical organisation. The main questions posed are the role of reproduction from seeds and the fact that the model routes sediment but not water. The model is unable therefore to produce features related to concentrated runoff, indirectly simulating the role of montane processes which disturb the organisation of incipient channel forms.

Assessing highway permeability for the restoration of landscape connectivity between protected areas in the Basque country, northern Spain.

Abstract Some highways were built in the Basque country before environmental impact assessment processes required the implementation of wildlife crossing structures. Some highway sectors were selected because they intersected with sites of high landscape connectivity between protected natural areas. These were identified using a Geographic Information System-based connectivity model that represented the spatial ecology of large and medium-sized mammal species. Permeability of road sectors was analysed by calculating the density of crossing structures considered adequate for target species and comparing it with the recommended density in technical prescriptions for new highways. Additionally, factors that could limit movement across these structures were also analysed, such as the shortage of forest cover in the surroundings or the presence of obstacles. An approximation of permeability deficits has been obtained, and a set of corrective measures that must be implemented into landscape defragmentation frameworks has been identified.

Doomed to collapse: Why Algerian steppe rangelands are overgrazed and some lessons to help land-use transitions

This work illustrates the application of a simulation model to analyse how swiftly large-scale land-use changes can drive broad territories to collapse. In this sense, the economic needs of a population should not clash with the natural environment but rather be reconciled with it. Abundant literature deals with the integration of socioeconomic drivers, ecological aspects, farming management, and climatology related to Algerian rangeland degradation. The present study seeks to compare the time course of Alfa grass biomass and the livestock raised on these distinctive rangelands under two different land-use strategies. The traditional one has nomads as the main inhabitants of these lands. For centuries, their strategy for alleviating pressure on resources was to move from one area to other. The more recent sedentary land-use leads to overgrazing supported by the massive use of cheap supplemental feed. Additionally, the model was used as a platform to launch scenarios for sustainable land-use management under a competitive market-economy. A key finding for preserving grazing resources was the increment of supplemental feed prices, which is compatible with stocking rates higher than the historical ones.

Land Degradation States and Trends in the Northwestern Maghreb Drylands, 1998–2008

States of ecological maturity and temporal trends of drylands in Morocco, Algeria and Tunisia north of 28°N are reported for 1998–2008. The input data were Normalized Difference Vegetation Index databases and corresponding climate fields, at a spatial resolution of 1 km and a temporal resolution of one month. States convey opposing dynamics of human exploitation and ecological succession. They were identified synchronically for the full period by comparing each location to all other locations in the study area under equivalent aridity. Rain Use Efficiency (RUE) at two temporal scales was used to estimate proxies for biomass and turnover rate. Biomass trends were determined for every location by stepwise regression using time and aridity as predictors. This enabled human-induced degradation to be separated from simple responses to interannual climate variation. Some relevant findings include large areas of degraded land, albeit improving over time or fluctuating with climate, but rarely degrading further; smaller, but significant areas of mature and reference vegetation in most climate zones; very low overall active degradation rates throughout the area during the decade observed; biomass accumulation over time exceeding depletion in most zones; and negative feedback between land states and trends suggesting overall landscape persistence. Semiarid zones were found to be the most vulnerable. Those results can be disaggregated by country or province. The combination with existing land cover maps and national forest inventories leads to the information required by the two progress indicators associated with the United Nations Convention to Combat Desertification strategic objective to improve the conditions of ecosystems and with the Sustainable Development Goal Target 15.3 to achieve land degradation neutrality. Beyond that, the results are also useful as a basis for land management and restoration.

Land degradation assessment by applying relative rue in Inner Mongolia, China, 2001–2010

Land degradation in Inner Mongolia, China is much severe. Remote sensing application on land degradation assessment can provide scientific basis for land degradation prevention in the study area. In this paper, land degradation was assessed by applying two improved relative Rain Use Efficiency (RUE) indicators based on time series MODIS NDVI data and high-resolution meteorological data from 2001 to 2010. The results show that 76.74% land of the whole study area with good or unusually good condition, it indicates that the most areas have normal or good vegetation production capacity. The unusually degraded and degraded lands account for 11.94% of the study area, especially they are less degraded lands distributing in Beijing and Tianjin sandstorm source region within the Inner Mongolia, it indicates that some ecological engineering projects implemented in this area have achieved significantly for restoration of degraded ecosystems in recent 10 years.

Desertification monitoring and assessment: A new remote sensing method

Desertification and restoration could be assessed by long time-series vegetation index at regional scale. In this study, a new approach for desertification assessment based on analysis of NPP and MNPP change derived from the time-series MERIS NDVI data was promoted. Desertification and restoration in Xilin Gol League, Inner Mongolia, China were assessed and monitored during 2003 to 2011 by using the new method. Results showed that the desertification is severe in study area, 17.2% of lands were suffered from desertification in Xilin Gol League during 2003 to 2011. The ecological engineering projects implemented in the study area have achieved significantly, especially in the Otindag Sandylands.