Rens van Beek

Vegetation succession and its consequences for slope stability in SE Spain.

The effect of land abandonment as a result of changing land-use policies is becoming more and more important throughout Europe. In this case study, the role of vegetation succession and landslide activity on steep abandoned slopes was investigated. The influence of vegetation succession on soil properties over time, as well as how developing root systems affect soil reinforcement was determined. The study was carried out in the Alcoy basin in SE Spain, where the marl substratum is prone to landsliding along steep ravines. The bench-terraced slopes have been abandoned progressively over the last 50 years and show various stages of revegetation. The study was carried out at two scales; at the catchment scale long-term evolution of land-use, vegetation succession and slope failure processes were investigated. At a more detailed scale, vegetation cover, soil properties and rooting effects on soil strength were determined.Results showed that the soil has changed over a period of 50 years with respect to soil properties, vegetation cover and rooting, which is reflected in the activity of geomorphological processes. Vegetation succession progressively limits surface processes (sheet wash and concentrated overland flow) over time, whereas slopes affected by mass wasting processes increase in number.The spatial heterogeneity of infiltration increases over time, leading to increased macro-pore flow towards the regolith zone, enhancing the potential risk of fast wetting of the regolith directly above the potential plane of failure, as was concluded from rainfall simulations. In situ experiments to determine soil shear strength in relation to rooting indicated that roots contributed to soil strength, but only in the upper 0.4 m of the soil. Most failures however, occur at greater depths (1.0–1.2 m) as anchorage by deeper roots was not effective or absent. The observed initial increase in mass wasting processes after land abandonment can therefore be explained in two ways: (1) the limited contribution of anchorage by root systems at potential slip planes which cannot counterbalance the initial decline of the terrace walls, and (2) the fast transfer of rainfall to the potential slip plane by macro-pores enhancing mass movements. However, after approximately 40 years of abandonment, mass wasting processes decline.

Toward global drought early warning capability: Expanding international cooperation for the development of a framework for monitoring and forecasting

Drought is a global problem that has far-reaching impacts, especially on vulnerable populations in developing regions. This paper highlights the need for a Global Drought Early Warning System (GDEWS), the elements that constitute its underlying framework (GDEWF), and the recent progress made toward its development. Many countries lack drought monitoring systems, as well as the capacity to respond via appropriate political, institutional, and technological frameworks, and these have inhibited the development of integrated drought management plans or early warning systems. The GDEWS will provide a source of drought tools and products via the GDEWF for countries and regions to develop tailored drought early warning systems for their own users. A key goal of a GDEWS is to maximize the lead time for early warning, allowing drought managers and disaster coordinators more time to put mitigation measures in place to reduce the vulnerability to drought. To address this, the GDEWF will take both a top-down approach...

Reply to comment by Keith J. Beven and Hannah L. Cloke on ''Hyperresolution global land surface modeling: Meeting a grand challenge for monitoring Earth's terrestrial water''

WATER RESOURCES RESEARCH, VOL. 48, W01802, doi:10.1029/2011WR011202, 2012 Reply to comment by Keith J. Beven and Hannah L. Cloke on ‘‘Hyperresolution global land surface modeling: Meeting a grand challenge for monitoring Earth’s terrestrial water’’ Eric F. Wood, 1 Joshua K. Roundy, 1 Tara J. Troy, 1 Rens van Beek, 2 Marc Bierkens, 2 Eleanor Blyth, 3 Ad de Roo, 4 Petra Doll, 5 Mike Ek, 6 James Famiglietti, 7 David Gochis, 8 Nick van de Giesen, 9 Paul Houser, 10 Peter Jaffe, 1 Stefan Kollet, 11 Bernhard Lehner, 12 Dennis P. Lettenmaier, 13 Christa D. Peters-Lidard, 14 Murugesu Sivapalan, 15 Justin Sheffield, 1 Andrew J. Wade, 16 and Paul Whitehead 17 Received 25 July 2011; revised 9 November 2011; accepted 3 December 2011; published 21 January 2012. Citation: Wood, E. F., et al. (2012), Reply to comment by Keith J. Beven and Hannah L. Cloke on ‘‘Hyperresolution global land surface modeling: Meeting a grand challenge for monitoring Earth’s terrestrial water’’ Water Resour. Res., 48, W01802, doi:10.1029/ 2011WR011202. Introduction [ 1 ] The authors of Wood et al. [2011, hereafter W2011] would like to thank Beven and Cloke [2012, hereafter BC2012] for furthering the discussion about the pathway to- ward a global-scale hyper-resolution water-energy-biogeo- chemistry land surface modeling capability: its need, feasibility and development. Their comment brings focus to the discussion and shows that the proposed challenge to our community is one element in a long history of hydrology Department of Civil and Environmental Engineering, Princeton Uni- versity, Princeton, New Jersey, USA. Department of Physical Geography, University of Utrecht, Utrecht, Netherlands. Centre for Ecology and Hydrology, Wallingford, UK. Institute for Environment and Sustainability, European Commission Joint Research Center, Ispra, Italy. Institute of Physical Geography, J. W. Goethe University, Frankfurt am Main, Germany. Environmental Modeling Center, National Centers for Environmental Protection, Suitland, Maryland, USA. UC Center for Hydrologic Modeling, University of California-Irvine, Irvine, California, USA. Research Applications Laboratory, National Center for Atmospheric Research, Boulder, Colorado, USA. Department of Water Management, Delft University of Technology, Delft, Netherlands. Department of Geography and GeoInformation Science, George Mason University, Fairfax, Virginia, USA. Meteorological Institute, University of Bonn, Bonn, Germany. Department of Geography, McGill University, Montreal, Quebec, Canada. Department of Civil and Environmental Engineering, University of Washington, Seattle, Washington, USA. Hydrological Sciences Laboratory, NASA Goddard Space Flight Cen- ter, Greenbelt, Maryland, USA. Department of Civil and Environmental Engineering and Department of Geography, University of Illinois Urbana-Champaign, Urbana, Illinois, USA. School of Human and Environmental Science, University of Reading, Reading, UK. School of Geography and the Environment, Oxford University, Oxford, UK. Copyright 2012 by the American Geophysical Union 0043-1397/12/2011WR011202 model developments with the goal to improving hydrologic predictions and understanding. [ 2 ] What is laid out in W2011 is, first and foremost, a grand challenge because (1) there is a grand need, (2) there are great new opportunities, and (3) if the hydrologic com- munity does not do it someone else will do it, albeit poorly. The reader is directed to W2011 for a discussion of the growing need for continental-scale land surface models that consider improved, scale-appropriate parameteriza- tions of the water, energy and biogeochemical cycles at resolutions on the order of 10 2 to 10 3 m grid resolutions. Some examples are presented, which were not meant be to comprehensive in their scope of detail, that include surface-subsurface interactions, land-atmospheric interac- tions and coupling, water quality that includes nonpoint pollution, and human impacts that include water manage- ment, land cover change and the effects of climate change. [ 3 ] The commentary by BC2012 focuses on just one chal- lenge or building block described in W2011: the issue of parameterization of subgrid heterogeneity and the resulting uncertainty—what they refer to as ‘‘epistemic uncertainty.’’ BC2012 interprets the Grand Challenge in W2011 as ‘‘simply moving to finer resolutions.’’ This is not what W2011 says or proposes. There are many new building blocks available for the research into hyper-resolution modeling: (1) new data sources and measurement techniques for precipitation, topog- raphy, vegetation cover, soils, but also soil moisture, evapo- transpiration, water storages (rivers, lakes, groundwater storages, soil moisture); (2) new physics—new sets of gov- erning equations, including new approaches to developing closure relations; (3) new approaches to handling known and unknown uncertainties in model structure, variables and numerics, including characterizing subgrid heterogeneity (including new ways to capture their effects) based on new insights into ecohydrology and hydropedology and approaches that utilize the coevolution of climate, soils, vege- tation and topography; (4) new approaches that can better include nonlinear feedbacks between various subsystems, and local, regional and global cycles and teleconnections; (5) new regionalization efforts aimed at learning from compara- tive analysis across climatic, geologic and human-impact W01802 1 of 3

Hillslope processes: Mass wasting, slope stability and erosion

This chapter describes the dominant types of processes present on hillslopes where both gravity and running water are active. The impact of natural hillslope processes is important and is currently strongly influenced by human activity due to land use change and vegetation removal, and is becoming even greater due to climate change. Both the fundamentals of erosion and slope stability are discussed in this chapter with respect to processes, causes and impacts. To fully appreciate the role of vegetation in the remediation of adverse slope processes, the fundamentals of these slope processes are addressed. In the first part, the role of mass movements is discussed. The definitions used and physical principles underlying mass movements are explained and keys and diagnostic parameters are given to explain how to recognize certain types of mass movements in the field. The causes of mass movement are described, amongst which deforestation, adverse hydrological conditions or slope undercutting, are summarized. The main types of mass movements i.e. falls, slides and flows are then separately discussed, giving full details with regard to their causes, processes and consequences, as well as a first glimpse to the solutions to slope failure problems, which will be addressed in more detail elsewhere in the book. The second part addresses erosion processes. Accelerated erosion is considered as one of the greatest problems of land degradation as it removes the fertile topsoil at high rates. Mankind, who is removing the original vegetation for agricultural purposes, is causing this problem. Again the general principles behind soil erosion are illustrated, giving attention to the causes and the different soil erosion processes such as sheet erosion, rill and gully erosion, piping and tunnel erosion as well as tillage erosion.

How the Stabilizing Effect of Vegetation on a Slope Changes Over Time: A Review

The principles of slope stabilization through vegetation are well known but substantial uncertainty remains about its transient effects, for example that of a forest stand throughout its life cycle. This comprises direct impacts but also more indirect ones that influence soil development that can be important but also difficult to observe and quantify. Often these effects are ambiguous, having potentially a stabilizing or destabilizing influence on a slope under particular conditions (e.g., more structured soils leading to both rapid infiltration and drainage).

Techniques for the modelling of the process systems in slow and fast-moving landslides

This chapter reviews some of the current strategies for landslide modelling. Main physical processes in landslides are first recalled. Numerical tools are then introduced for the analysis of the behaviour of slow- and fast-moving landslides. Representative case studies are introduced through the chapter to highlight how different modelling strategies can be used depending on the physical processes that the modeller wants to take into account.

Skill of a global forecasting system in seasonal ensemble streamflow prediction

In this study we assess the skill of seasonal streamflow forecasts with the global hydrological forecasting system Flood Early Warning System (FEWS)-World, which has been set up within the European Commission 7th Framework Programme Project Global Water Scarcity Information Service (GLOWASIS). FEWS-World incorporates the distributed global hydrological model PCR-GLOBWB (PCRaster Global Water Balance). We produce ensemble forecasts of monthly discharges for 20 large rivers of the world, with lead times of up to 6 months, forcing the system with biascorrected seasonal meteorological forecast ensembles from the European Centre for Medium-range Weather Forecasts (ECMWF) and with probabilistic meteorological ensembles obtained following the ESP procedure. Here, the ESP ensembles, which contain no actual information on weather, serve as a benchmark to assess the additional skill that may be obtained using ECMWF seasonal forecasts. We use the Brier skill score (BSS) to quantify the skill of the system in forecasting high and low flows, defined as discharges higher than the 75th and lower than the 25th percentiles for a given month, respectively. We determine the theoretical skill by comparing the results against model simulations and the actual skill in comparison to discharge observations. We calculate the ratios of actual-to-theoretical skill in order to quantify the percentage of the potential skill that is achieved. The results suggest that the performance of ECMWF S3 forecasts is close to that of the ESP forecasts. While better meteorological forecasts could potentially lead to an improvement in hydrological forecasts, this cannot be achieved yet using the ECMWF S3 dataset.

Integration of Geometrical Root System Approximations in Hydromechanical Slope Stability Modelling

Spatially distributed physically based slope stability models are commonly used to assess landslide susceptibility of hillslope environments. Several of these models are able to account for vegetation related effects, such as evapotranspiration, interception and root cohesion, when assessing slope stability. However, particularly spatial information on the subsurface biomass or root systems is usually not represented as detailed as hydropedological and geomechanical parameters. Since roots are known to influence slope stability due to hydrological and mechanical effects, we consider a detailed spatial representation as important to elaborate slope stability by means of physically based models. STARWARS/PROBSTAB, developed by Van Beek (2002), is a spatially distributed and dynamic slope stability model that couples a hydrological (STARWARS) with a geomechanical component (PROBSTAB). The infinite slope-based model is able to integrate a variety of vegetation related parameters, such as evaporation, interception capacity and root cohesion. In this study, we test two different approaches to integrate root cohesion forces into STARWARS/PROBSTAB. Within the first approach, the spatial distribution of root cohesion is directly related to the spatial distribution of land use areas classified as forest. Thus, each pixel within the forest class is defined by a distinct species related root cohesion value where the potential maximum rooting depth is only dependent on the respective species. The second method represents a novel approach that approximates the rooting area based on the location of single tree stems. Maximum rooting distance from the stem, maximum depth and shape of the root system relate to both tree species and external influences such as relief or soil properties. The geometrical cone-shaped approximation of the root system is expected to represent more accurately the area where root cohesion forces are apparent. Possibilities, challenges and limitations of approximating species-related root systems in infinite slope models are discussed.