Water-soil-vegetation dynamic nexuses affect, and are affected by, both human activity and climate change. Inappropriate land management practices can result in soil and vegetation degradation, which in turn will likely alter natural hydrologic processes, leading to more frequent and severe flooding and drought. In response, an altered hydrologic condition tends to prompt soil erosion by wind and water, which can cause further vegetation degradation or even loss. Such nexuses will likely become more interwoven in changing climate because the non-stationary climate can further deteriorate the already-altered hydrologic condition. So far, our understanding is incomplete regarding how such nexuses maintain or break equilibriums between water, soil, and/or vegetation in terms of eco-environmental resilience. This book: 1) conceptualises the interrelated physical processes of water-soil-vegetation systems; 2) introduces mathematical models for simulating the processes; and 3) develops a variety of modelling cases of selected systems across the world.
Water-soil-vegetation dynamic nexuses affect, and are affected by, both human activity and climate change. For a given area, inappropriate land management practices can result in soil and vegetation degradation, which in turn will likely alter natural hydrologic processes, leading to more frequent and severe flooding and drought. In response, an altered hydrologic condition tends to prompt soil erosion by wind and water, which can cause further vegetation degradation or even loss. Such nexuses will likely become more interwoven in changing climate because the non-stationary climate can further deteriorate the already-altered hydrologic condition. So far, our understanding is incomplete regarding how such nexuses maintain or break equilibriums between water, soil, and/or vegetation in terms of eco-environmental resilience. This book: 1) conceptualises the interrelated physical processes of water-soil-vegetation systems; 2) introduces mathematical models for simulating the processes; and 3) develops a variety of modelling cases of selected systems across the world. Currently, there are no books focusing on this topic though some incomplete information has been scattered in various peer-reviewed journals and project reports. This book provides a systematic elucidation of this important topic and serves as a one-stop information source. Upon reading this book, the reader can apply the materials to conduct advanced research on this topic and develop practical measures in protecting fragile vegetation ecosystems and confronting climate change. The broader application is to prevent land degradation and desertification as induced by climate change and human activities (e.g., development and grazing). Recommended for researchers and graduate students. Key Features: Includes both fundamental principles and practical applications Emphasizes semiarid water-soil-vegetation nexuses rather than individual processes Deciphers dynamics and interrelations of the physical processes of semiarid water-soil-vegetation systems Addresses impacts of climate change from practical management perspectives Maximizes readability by including illustrations, pictures, and annotated equations.
Arid and semi-arid regions are defined as areas where water is at its most scarce. The hydrological regime in these areas is extreme and highly variable, and they face great pressures to deliver and manage freshwater resources. However, there is no guidance on the decision support tools that are needed to underpin flood and water resource management in arid areas. UNESCO initiated the Global network for Water and Development Information for arid lands (GWADI), and arranged a workshop of the world's leading experts to discuss these issues. This book presents chapters from contributors to the workshop, and includes case studies from the world's major arid regions to demonstrate model applications, and web links to tutorials and state-of-the-art modelling software. This volume is a valuable reference for researchers and engineers working on the water resources of arid and semi-arid regions.
Arid and semi-arid regions face major challenges in the management of scarce freshwater resources under pressures of population, economic development, climate change, pollution and over-abstraction. Groundwater is commonly the most important water resource in these areas. Groundwater models are widely used globally to understand groundwater systems and to guide decisions on management. However, the hydrology of arid and semi-arid areas is very different from that of humid regions, and there is little guidance on the special challenges of groundwater modelling for these areas. This book brings together the experience of internationally leading experts to fill a gap in the scientific and technical literature. It introduces state-of-the-art methods for modelling groundwater resources, illustrated with a wide-ranging set of illustrative examples from around the world. The book is valuable for researchers, practitioners in developed and developing countries, and graduate students in hydrology, hydrogeology, water resources management, environmental engineering and geography.
Current climate change trends are affecting the magnitude and recurrence of extreme weather events. In particular, several semi-arid regions around the planet are confronting more intense and prolonged lack of precipitation, slowly transforming these regions into deserts. In this thesis we present a stochastic (meso-scale) model for vegetation-precipitation interactions for semi-arid landscapes. Extensive simulations with the model suggest that persistence in current trends of precipitation decline in semi-arid landscapes may expedite desertification processes by up to several decades.
Water-Soil-Vegetation Nexus and Climate Change presents a broad overview of the research needs and approaches regarding water-soil-vegetation nexus and climate change. It includes chapters discussing water budget and factors that affect hydrologic processes such as precipitation, runoff, infiltration, evapotranspiration, soil water, and groundwater, in addition to a focus on consumptive (e.g., domestic and irrigation) and non-consumptive (e.g., eco-environmental) water uses, and water shortage. Throughout Water-Soil-Vegetation Nexus and Climate Change chapters specifically deal with the fundamental principles and also case studies, applications, and decision support tools, that can be usable for developing practical management measures in sustaining our eco-environment and society by maintaining an optimal water-soil-vegetation equilibrium. Written with water resources students and professors in mind, this book will provide the reader with further knowledge on the water-soil-vegetation nexus and its connection to climate change. - Includes both principles and applications, providing the reader with options for both application types as needed - Emphasizes the nexuses rather than individual processes, allowing the reader to understand the whole picture - Presents case studies and decision support tools that can be used for developing practical management measures in changing climate
CD-ROM Water availability is one of the main limiting factors that control ecosystem functions and productivity in semiarid regions. Vegetation of these regions usually presents a patchy distribution where sparse plant cover is interspersed over a bare soil. During the few rainfall events, runoff is generated in non-vegetated areas and redistributed towards vegetation, which act as surface obstruction for water, sediments and nutrients. Thus, non-vegetated areas are more susceptible to water erosion processes. Non-vegetated areas from semiarid ecosystems around the world, are often covered by Biological Soil Crusts (BSCs). BSCs result from an intimate association between soil particles and cyanobacteria, algae, microfungi, lichens and bryophytes. These communities live within, or immediately on top of, the uppermost millimeters of soil, influencing soil surface properties involved in infiltration, runoff generation and water erosion. Several papers have demonstrated that BSCs are one of the most important soil stabilizing factors in drylands. There are, however, contradictory results on the role that BSCs play in regulating soil water fluxes. Some studies point BSCs as runoff sources that may increase downslope erosion or on the contrary may represent an additional supply of water for downslope vegetation allowing its survival. The impact of this additional runoff should be evaluated at less detailed scales than the patch and to analyze all interactions in terms of water, sediments and nutrients between areas covered by BSCs and vegetated patches in order to establish the real effects of BSCs on both runoff and erosion. Also, to correctly predict the impact of future climate changes or antropic disturbances on hydrological behavior and water erosion in systems dominated by BSCs their effects should be included on spatially distributed runoff and erosion models. Until now, the influence of BSCs on these processes has been addressed almost exclusively at patch scale, despite the fact some authors have pointed the need of upscaling their effects, and even more their influence on runoff generation and water erosion was never considered in spatially implicit medelling. The goal of this thesis is to determine BSC effects on runoff and water erosion from plot to catchment scale in a typical semiarid ecosystem. To achieve this objective, first direct and indirect effects of BSCs at patch scale must be clearly defined under natural rainfall conditions to solve the controversy about BSCs effects on runoff generation. To know the direct and indirect relationships among soil surface characteristics, BSC cover and type, topography, rainfall characteristics (duration, amount and intensity) and runoff, structural equation models (SEM) were applied. Our results reveal the critical importance of BSCs on runoff and water erosion. Both processes in biologically crusted areas are directly controlled by crust type and cover. BSCs also modified some soil surface properties involved in runoff generation and water erosion, such as microtopography, surface stability or water repellency. The final interaction of both, direct and indirect BSCs effects, determine the hydrological behavior of these surfaces under natural rainfall conditions. Moreover, the final effect of BSCs on runoff generation is strongly driven by rainfall properties, which determined the set of complex interactions among BSCs, type and developmental stage and soil surface properties: on one hand, during low intensity rains, BSC-induced microtopography increases the amount of surface micro-depressions, which act as temporal water sinks, reducing the connectivity among source areas, delaying runoff initiation and reducing runoff rates; on the other hand, during intense rainfall events, BSCs type and water repellency are the main factors determining runoff generation. When the effects of BSCs are analyzed at coarser scales, including all interactions among BSCs and vegetated areas on a whole catchment, our results reveal the importance of the interactions between areas with BSCs and areas with vegetation on runoff generation and water erosion. We show the capacity of vegetated areas to retain runoff waters generated by upslope biologically crusted areas as an important driver for the hydrological and erosional response at catchment scale. However, the capability of vegetated areas to trap and retain water and sediments is limited and can be exceeded during high magnitude events, increasing catchment connectivity, as well as runoff and water erosion at the catchment outlet. Even during high-magnitude events, when the runoff generated in BSC areas reaches the channel network, the local protection provided by BSCs also affects downslope areas and the catchment response. These results confirm that BSCs must be included in runoff and soil erosion models to obtain reliable predictions of the spatial pattern of runoff and water erosion in catchments with abundant BSCs. In order to correctly introduce the effects of BSCs in these models, it is necessary to have an accurate spatial characterization of BSCs. It is shown that a spectral mixture analysis is required for the precise characterization of the complex spatial distribution of BSCs, due to the intrinsic spatial heterogeneity of semiarid ecosystems and to the spectral similarities among BSCs, dry vegetation and bare soil. Due to the methodological and practical application problems of spectral mixture analysis when it is applied to spectrally complex areas or when some surface elements only appear in specific areas of the image, we needed to develop a novel methodology for BSCs classification and quantification (lichen and cyanobacteria-dominated CBS), based on hyperspectral images. Support vector machine classification was applied for spectral and ecological classification of homogenous areas to solve the mentioned problems inherent to spatial heterogeneity. Inmediately afterwards, spectral mixture analysis (SMA) was applied to each SVM class to quantify the proportion of each type of surface cover within each pixel. Relative abundance images obtained with this methodology achieve a relatively high accuracy for different types of BSCs, and have demonstrated to be an adequate source of spatially distributed information, to correctly characterize surface properties in biologically crusted drylands systems. Moreover, to have the spatial distribution of type and abundance of BSCs allows to increase the accuracy of modeled runoff and erosion. Thus, when BSCs effects are not included in the LISEM model, an important increase in modeled water erosion was observed in areas where BSCs was not considered.
