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Badlands are landforms that occur all over the World. In the Mediterranean region, badlands are found in both dry (arid and semi‐arid) and wet (subhumid and humid) environments, and are characterized by complex hydro‐geomorphological dynamics, high intense erosion processes and extreme sediment yield. Understanding the impact of Global Change is key to predict the on‐site and off‐site effects on badland dynamics, particularly its consequences on bedrock weathering, on sediment yield and delivery and on plant colonization. Here, conducting a systematic literature review, we analyzed an extensive database and identified the main climate‐drivers affecting the hydro‐geomorphological dynamics in Mediterranean badlands (based on non‐metric multidimensional scaling and structural equation modeling analysis). Later, we examined the main impacts expected from climate change forecasting in the near future, and we explored the interactions between badlands response to climate variation. In Mediterranean badlands, weathering processes are mainly related to wetting–drying cycles and freeze–thaw cycles in dry and wet badlands, respectively. In both environments, rainfall amount appears as the main driver for runoff response, and rainfall amount and rainfall intensity for erosion dynamics. Future climate scenarios forecast a decrease in annual rainfall, number of rainfall events and frost days, and in soil moisture, and an increase in rainfall intensity. These changes will have direct hydro‐geomorphological implications with direct and indirect effects on badland dynamics. This may result in a decrease in annual runoff in dry badlands, but the occurrence of more frequent extreme events would increase soil erosion and could negatively affect biological soil crust. In wet badlands, weathering and erosion processes may decrease, and a stabilization of the slopes, with consequently improved vegetation growth, may be expected. In addition, the forecasted changes must be taken into account, especially considering the possible off‐site effects of these extreme environments. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we investigated rainfall, run‐off, and sediment transport dynamics (414 run‐off events and 231 events with sediment information) of a humid mountain badland area—the Araguás catchment (Central Pyrenees, Spain)—from October 2005 to September 2016. Use of this long‐term database allows characterization of the hydrological response, which consist of low‐magnitude/high‐frequency events and high‐magnitude/low‐frequency events, and identification of seasonal dynamics and rainfall‐run‐off thresholds. Our results indicate that the Araguás catchment, similarly to other humid badlands, had high hydrological responsiveness (mean annual run‐off coefficient: 0.52), a non‐linear relationship of rainfall with run‐off (common in Mediterranean environments), and seasonal hydrological and sedimentological dynamics. We created and validated a multivariate regression model to characterize the hydrological variables (stormflow and peak discharge) and sedimentological variables (mean and maximum suspended sediment concentrations and total suspended sediment load). In summer and at the beginning of autumn, the response was mainly related to rainfall intensity, suggesting a predomination of Hortonian flows. In contrast, in spring and winter, the responses were mainly related to the antecedent conditions (previous rainfall and baseflow), suggesting the occurrence of saturated excess flow processes, and the contribution of neighbouring vegetated areas. The multivariate analysis also showed that total sediment load is better predicted by a multivariate regression model that integrates pre‐event, rainfall, and run‐off variables. In general, our models provided more accurate predictions of small‐magnitude/high‐frequency events than high‐magnitude/low‐frequency events. This study highlights the high inter‐ and intra‐annual variability response in humid badland areas and that long‐term records are needed to reduce the uncertainty of hydrological and sedimentological responses in Mediterranean badland areas. [ABSTRACT FROM AUTHOR]

ABSTRACT Soil erosion is one of the most severe land degradation processes in the Mediterranean region. Although badlands occupy a relatively small fraction of the Mediterranean area, their erosion rates are very high. Many studies have investigated to what extent vegetation controls soil erosion rates. This study, however, deals with the impact of erosion on vegetation establishment. In semi-arid badlands of the Mediterranean, soil water availability constitutes the main limiting factor for vegetation development. As a consequence, south-facing slopes are typically less vegetated due to a very large water stress. However, these findings do not necessarily apply to humid badlands. The main objective of this paper is to determine the topographic thresholds for plant colonization in relation to slope aspect and to assess the spatial patterns of vegetation cover and species richness. We surveyed 179 plots on highly eroded badland slopes in the Central Pyrenees. We defined four aspect classes subdivided into slope angle classes. Colonization success was expressed in terms of vegetation cover and species richness. Slope angle thresholds for plant colonization were identified for each slope aspect class by means of binary logistic regressions. The results show that a critical slope angle exists below which plants colonize the badland slopes. Below this critical slope angle, plant cover and species richness increase with a decreasing slope angle. The largest critical slope angles in humid badlands are observed on south-facing slopes, which contrasts with the results obtained in semi-arid badlands. North-facing slopes however are characterized by a reduced overall vegetation cover and species richness, and lower topographic threshold values. The possible underlying processes responsible for this slope-aspect discrepancy in vegetation characteristics are discussed in terms of environmental variables that control regolith development, weathering and erosion processes. Moreover, possible restoration strategies through the use of vegetation in highly degraded environments are highlighted. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Intense erosion processes are widespread in the Mediterranean region, and include sheet wash erosion, rilling, gullying, shallow landsliding, and the development of large and active badlands in both subhumid and semi-arid areas. This review analyses the main environmental and human features related to soil erosion processes, and the main factors that explain the extreme variability of factors influencing soil erosion, particularly recent land use changes. The importance of erosion in the Mediterranean is related to the long history of human activity in a region characterized by low levels of annual precipitation, the occurrence of intense rainstorms and long-lasting droughts, high evapotranspiration, the presence of steep slopes and the occurrence of recent tectonic activity, together with the recurrent use of fire, overgrazing and farming. These factors have resulted in a complex landscape in which intensification and abandonment, wealth and poverty can co-exist. The changing conditions of national and international markets and the evolution of population pressure are now the main drivers explaining land use changes, including farmland abandonment in mountain areas, the expansion of some subsidized crops to marginal lands, and the development of new terraces affected by landslides and intense soil erosion during extreme rainstorm events. The occurrence of human-related forest fires affecting thousands of hectares each year is a significant problem in both the northern and southern areas of the Mediterranean basin. Here, we highlight the rise of new scientific challenges in controlling the negative consequences of soil erosion in the Mediterranean region: 1) to reduce the effects and extent of forest fires, and restructure the spatial organization of abandoned landscapes; 2) to provide guidance for making the EU agricultural policy more adapted to the complexity and fragility of Mediterranean environments; 3) to develop field methods and models to improve the identification of runoff and sediment contributing areas; 4) to contribute to the conservation of landscapes (i.e. bench-terraced fields) having high cultural and productivity values; 5) to improve knowledge of the hydrological and geomorphological functioning of badlands, with the aim of reducing sediment yield and accessibility; 6) to better understand the effect of climate change on soil erosion in the Mediterranean region; and 7) to improve quantitative information on long-term soil erosion. [Copyright &y& Elsevier]

Badlands are important in terms of sediment yield, particularly in mountain areas having subhumid and humid climatic conditions. Various studies concerning erosion and hydrological processes have demonstrated that suspended sediment transport is probably the main process in sediment export from badland areas. In the Araguás catchment (central Pyrenees) there is a statistically significant positive linear relationship between maximum discharge and the maximum suspended sediment concentration (SSC). The high frequency of hyper-concentrated fluxes of SSC (>500g·l−1) recorded at two gauging stations close to badland areas in the Pyrenees (Araguás) and the Alps (Draix) indicates that these fluxes are not uncommon, and suggests that they may transport relatively large suspended particles, especially during extreme floods. In a study involving sampling during two moderate floods (August 2006 and February 2007) in the Araguás catchment it was observed that the mean suspended sediment particle size was significantly greater during the highest SSC conditions. The results showed the great heterogeneity of particle sizes that can affect suspended sediment transport, which is usually estimated from concentration determined from turbidity values obtained using infrared devices and associated with the corresponding discharge value. Infrared turbidimeters have problems in detecting particles with a diameter (D)>0.1mm, although discharge can be evaluated with relative high accuracy. The combination of these factors suggests that the evaluation of sediment yield from badland areas using turbidity values involves significant uncertainty. If most suspended sediment is transported during moderate–high floods, which carry large quantities of suspended particles having D>0.1mm, then the sediment yield will be underestimated. The uncertainty can be calculated by determining the percentage and mean diameter of particles not detected, and the specific weight of the material. However, the uncertainty is not linear because of the exponential relationship between increasing diameter and the volume/mass, and consequently the error will increase with the growth in the suspended concentration. In this study the physical factors associated with uncertainty in the estimation of sediment yield were investigated, and quantitative estimates of the errors involved are provided. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the use of remote sensing data and GIS techniques in identifying badland areas and erosion risk areas, assessing the magnitude and rate of erosion processes, and estimating the geographical factors that control erosion. The remote sensing information was generated from Landsat TM and Landsat ETM+ images for the period 1984–2006, which were merged with aerial photographs. The study was performed on a 73km2 area in a corridor of Eocene marls in the Pre-Pyrenees, an area highly prone to erosion processes. The results show that badland areas occupy approximately 2km2 and are widespread in the study area. Various spectral indices were assessed for their performance in revealing badland dynamics; all were very useful for this purpose, and few differences were found among them. From the results we recommend the use of the simplest and most widely used spectral index: the normalized difference vegetation index (NDVI). Further analyses showed that there was a clear difference between the vegetated and degraded areas. The degraded areas showed a dominant negative trend of NDVI values, which is indicative of possible degradation processes and an increase in the surface area affected by erosion. We concluded that the degraded areas, which had poor vegetation cover and extreme environmental conditions, show a spatial pattern related to topographical location, and particularly the presence of north-facing slopes. A map of possible erosion risk was generated as a function of the initial environmental conditions and the evolution of erosion from 1984 to 2006. [Copyright &y& Elsevier]

Badlands are landforms that occur all over the world. The term "badlands" refers to regions that have soft and poorly consolidated material outcrops, limited vegetation, reduced or no human activity, and a wide range of geomorphic processes, such as weathering, erosion, landslides, and piping. These features interact at different spatial and temporal scales to shape these distinct landforms (Martínez-Murillo and Nadal-Romero, 2018). A recent published review in 2018 (Nadal-Romero et al., 2018) classified the most important topics studied until now in badlands researches as follow: (i) origins, (ii) lithology, (iii) human activities and land uses, (iv) vegetation (seeds and seedlings), (v) hydrology, (vi) piping, (vii) erosion processes and erosion rates, (viii) new emerging methodologies, (ix) reclamation and restoration, (x) geoheritage and geotourism, and (xi) modelling.Thus, there are numerous studies already done until now, but the study of badlands is still relevant, especially, in the context of Global Change, and new questions should stimulate future badlands research. Many uncertainties remain and many topics are still open for research. We suggest that five important global issues or approaches should be considered in future studies of badlands: (i) use of holistic research, because badlands are complex systems; (ii) identification of the critical thresholds of precipitation, topography, and other factors that are responsible for the initiation and development of badlands in different climates; (iii) comparative studies of badlands with different rock types and climates; (iv) acquisition of long-term quantitative information, and new methods and models to identify water and sediment source areas; and (v) elucidation of how badlands may respond to Global Change.The scientific discussion about these topics is crucial to focus research questions and apply the wide range of existent techniques and methodologies, as well as to develop new ones, in order to answer them. The Global Change act all over the world and badlands are a perfect laboratory to assess the on and off-site impacts on current badland areas as well as to anticipate which ones may develop the processes that leading to the appearance of new badland areas.ReferencesMartínez-Murillo, J.F., Nadal-Romero, E. 2018. Perspectives on Badland Studies in the Context of Global Change. In: E. Nadal-Romero, J.F. Martínez-Murillo, N. Khun, Badlands Dynamics in the Context of Global Change. Elsevier, Amsterdam, pp. 1-26.Nadal-Romero, E., Martínez-Murillo, J.F., Khun, N. 2018. Badlands Dynamics in the Context of Global Change. Elsevier, Amsterdam, 320 p. [ABSTRACT FROM AUTHOR]