HYDRUS is a Windows-based modeling software package that can be used to analyze water flow and heat and solute transport in variably saturated porous media (e.g., soils or the vadose zone). The HYDRUS software includes an interactive graphics-based interface for data preprocessing, soil profile discretization, and graphic presentation of the results. Historically, HYDRUS consisted of two independent software packages. While HYDRUS-1D simulated flow and transport processes in one dimension and was a public domain software, HYDRUS (2D/3D; and earlier HYDRUS-2D) extended the simulation capabilities to the second and third dimensions and was distributed commercially. These two previously independent software packages were merged in 2023 into a single software package called HYDRUS.
The capabilities of the HYDRUS software packages have been significantly expanded by various standard and nonstandard specialized add-on modules. The standard add-on modules are fully incorporated and supported by the HYDRUS graphical user-friendly interfaces (GUIs) and documented in detail in the technical and user manuals. This is not the case for several additional nonstandard modules, which require additional work outside the GUI. A commonality of all HYDRUS add-on modules is that they simulate variably saturated water flow and heat and solute transport in porous media. The specialized add-on modules provide additional capabilities, such as considering general reactive transport (in the HPx models) or reactive transport with specific chemistry (notably the Wetland and UNSATCHEM modules). Other modules provide additional flow and/or transport modeling processes, such as to account for preferential flow (the DualPerm module), colloid-facilitated solute transport (the C-Ride module), or the transport of polyfluoroalkyl substances (PFAS; the PFAS module) or fumigant (the Fumigant module) compounds.
The HYDRUS models are among the most widely used numerical models for simulating processes in the subsurface. There are many thousands of HYDRUS users worldwide, with many applications (also several thousand) appearing in peer-reviewed international literature and many technical reports.
Article
The Family of HYDRUS Models
Jiří Šimůnek, Giuseppe Brunetti, Martinus Th. van Genuchten, and Miroslav Šejna
Article
Water Governance in the Netherlands
M.L. (Marie Louise) Blankesteijn and W.D. (Wieke) Pot
Dutch water governance is world famous. It to a large extent determines the global public image of the Netherlands, with its windmills, polders, dikes and dams, and the eternal fight against the water, symbolized by the engineering marvel of the Delta Works. Dutch water governance has a history that dates back to the 11th century. Since the last 200 years, water governance has, however, undergone significant changes. Important historical events setting in motion longer-term developments for Dutch water governance were the Napoleonic rule, land reclamation projects, the Big Flood of 1953, the Afsluitdijk, the impoldering of the former Southern Sea, the ecological turn in water management, and the more integrated approach of “living with water.” In the current anthropocentric age, climate change presents a key challenge for Dutch water governance, as a country that for a large part is situated below sea level and is prone to flooding.
The existing Dutch water governance system is multilevel, publicly financed, and, compared to many other countries, still relatively decentralized. The responsibilities for water management are shared among the national government and Directorate-General for Public Works and Water Management, provinces, regional water authorities, and municipalities. Besides these governmental layers, the Delta Commissioner is specifically designed to stimulate a forward-looking view when it comes to water management and climate change. With the Delta Commissioner and Delta Program, the Netherlands aims to become a climate-resilient and water-robust country in 2050.
Robustness, adaptation, coordination, integration, and democratization are key ingredients of a future-proof water governance arrangement that can support a climate-resilient Dutch delta. In recent years, the Netherlands already has been confronted with many climate extremes and will need to transform its water management system to better cope with floods but even more so to deal with droughts and sea-levels rising. The latest reports of the Intergovernmental Panel for Climate Change show that more adaptive measures are needed. Such measures also require a stronger coordination between governmental levels, sectors, policies, and infrastructure investments. Furthermore, preparing for the future also requires engagement and integration with other challenges, such as the energy transition, nature conservation, and circular economy. To contribute to sustainability goals related to the energy transition and circular economy, barriers for technical innovation and changes to institutionalized responsibilities will need to be further analyzed and lifted.
To govern for the longer term, current democratic institutions may not always be up to the task. Experiments with deliberative forms of democracy and novel ideas to safeguard the interests of future generations are to be further tested and researched to discover their potential for securing a more long-term oriented and integrated approach in water governance.
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Field-Level Irrigation
Kiril Manevski and Mathias Neumann Andersen
Field irrigation is the largest consumer of freshwater in the world covering 63 million hectares in the 1900s to 300 million hectares in the early 2000s to provide a multitude of benefits and ecosystem services to people around the globe, such as consistent food supply, higher crop productivity, and shared resource collectivism. Field irrigation intensifies land use mostly in the arid and the semiarid regions where precipitation cannot fully satisfy human and crop water demands. Climate change impacts the distribution and the timing of water availability into humid regions as well through increases in drought frequency and intensity, further augmenting the demand for irrigation. However, designing and operating irrigation infrastructure and scheduling practices for an agricultural region requires sound contemporary and historical knowledge of the local circumstances vis-à-vis humans, crops, soils, hydrology, and climate. Sub-Saharan Africa stands as a large-scale narrative of poorly performing field irrigation against decades of investments due to designs exclusive to the socioeconomic ecosystems. Optimal water allocation in the water–energy–environment–food nexus to achieve the greatest social and economic benefit for the region invariably a task of continuous cocreation between many actors. Therefore, field irrigation remains a challenging project and most of the agricultural water use worldwide—both from groundwater and surface water—remains suboptimal in terms of design, water allocation, and monitoring for farmers, communities, and regulators. Many diversions of surface water for irrigation in both economically developed and developing countries are small-scale temporary infrastructures in and outside official plans and permits, which altogether results in severe aquifer depletion worldwide with negative impacts on food safety, economy, environment, and society.
Traditional surface flooding is the dominant mode of irrigation globally and mostly applied on new agricultural fields, whereas water-saving irrigation methods are practiced on fewer and older fields. Water-saving technologies involve either scheduling of regulated deficit irrigation or local water storage to optimize crop water supply, which may be combined with drip irrigation, biodegradable soil amendments to retain soil water, and plastic mulches to minimize evaporation, whereas the use of partial root zone drying and biochar mostly remain at the experimental stage. Global analyses over the late 20th and early 21st century find no water saving by water-saving technologies at field scale because increased return flow from newly irrigated fields surpasses the reduced soil evaporation from old, irrigated fields, whereas regionally, return flow to fresh aquifers is a benefit rather than a loss, which results in some water savings. At the same time, increased crop transpiration exceeds regional water savings, which explains the paradox between the wide application of water-saving technologies and more severe regional water shortage.
With nonscientific decisions on when and where to irrigate practiced by most farmers worldwide, scheduling remains the top priority task in field irrigation, as both too little and too much water leads to yield decreases and loss of nutrients to the environment. Where water is abundant, scheduling aims to keep crop transpiration and yield at a maximum with minimum use of irrigation water. In dryer areas, this luxury can rarely be sustained unless the irrigation area and therefore production is reduced. Instead, regulated deficit irrigation may be practiced on drought-tolerant crops and cultivars. Regulated deficit irrigation seeks to limit crop transpiration to a fraction of the maximum during less drought-sensitive growth stages. In this way, crop water use efficiency increases, and yield per m3 of water rather than m2 of land is maximized. Remote sensing of soil and crops through satellite and aerial multispectral and thermal products have the potential to enhance irrigation scheduling by precisely quantifying and distinguishing crop transpiration (beneficial water consumption) from soil evaporation (nonbeneficial water loss) in space and time and to facilitate regulated deficit irrigation and other water-saving measures. However, irrigation management significantly falls behind in adapting state of the art information and communication technologies.
With a global rise in frequency and duration of droughts, the lack of irrigation infrastructure in humid regions and of water availability in semiarid regions induces enormous losses in agricultural production and social well-being and unveils an urgent need for a macrolevel drought governance approach in order to strengthen multisectoral water management and mitigate climate change damage to human and natural assets.
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The Allocation of Groundwater: From Superstition to Science
Burke W. Griggs
Groundwater is a critical natural resource, but the law has always struggled with it. During the 19th and early 20th centuries, the common law developed several doctrines to allocate groundwater among competing users. The groundwater revolution of the mid-20th century produced an explosive growth in pumping worldwide—and quickly exposed the flaws of these doctrines. Legal rules predicated on land and on surface waters could not meet the challenges posed by the common-pool groundwater resource: those of understanding groundwater dynamics, quantifying the impacts of pumping on other water rights, and devising satisfactory remedies. Unfettered by received property restraints, pumping on an industrial, aquifer-wide scale depleted and contaminated aquifers, regardless of doctrine.
The groundwater revolution motivated significant legal developments. Starting in the 1970s, the Supreme Court of the United States adapted its methods for resolving interstate water disputes to include the effects of groundwater pumping. This jurisprudence has fundamentally influenced international groundwater law, including the negotiation of trans-boundary aquifer agreements. Advances in hydrogeology and computer groundwater modeling have enabled states and parties to evaluate the effects of basin-wide pumping. Nonetheless, difficult legal and governance problems remain. Which level of government—local, state, or national—should exercise jurisdiction over groundwater? What level of pumping qualifies as “safe yield,” especially when the aquifer is overdrawn? How do the demands of modern environmental law and the public trust doctrine affect groundwater rights? How can governments satisfy long-neglected claims to water justice made by Indigenous and minority communities? Innovations in groundwater management provide promising answers. The conjunctive management of surface and groundwater can stabilize water supplies, improve water quality, and protect ecosystems. Integrated water resources management seeks to holistically manage groundwater to achieve social and economic equity. Water markets can reward water conservation, attract new market participants, and encourage the migration of groundwater allocations to more valuable uses, including environmental uses.
The modern law of groundwater allocation combines older property doctrines with 21st-century regulatory ideals, but the mixture can be unstable. In nations with long-established water codes such as the United States, common-law Anglophone nations, and various European nations, groundwater law has evolved, if haltingly, to incorporate permitting systems, environmental regulation, and water markets. Elsewhere, the challenges are extreme. Long-standing calls for groundwater reform in India remain unheeded as tens of millions of unregulated tube wells pump away. In China, chronic groundwater mismanagement and aquifer contamination belie the roseate claims of national water law. Sub-Saharan nations have enacted progressive groundwater laws, but poverty, racism, and corruption have maintained grim groundwater realities. Across the field, experts have long identified the central problems and reached a rough consensus about the most effective solutions; there is also a common commitment to secure environmental justice and protect groundwater-dependent ecosystems. The most pressing legal work thus requires building practical pathways to reach these solutions and, most importantly, to connect the public with the groundwater on which it increasingly depends.
Article
Water as a Merit Good
Michael Hanemann and Dale Whittington
In economics, a merit good is a good which it is judged that an individual or group of individuals should have (at least up to a certain quantity) on the basis of some concept of need, rather than on the basis of ability or willingness to pay. Examples include public elementary education and free hospitals for the poor alongside access to safe, affordable, and reliable water and sanitation. Exactly how a merit good is provided can be subjected to an economic test, but not whether the merit good should be provided. While there are some overlaps in application, the concept of a merit good is distinct from other economic concepts: A merit good may or may not be a public good, and it may or may not involve an externality. However, water and sanitation infrastructure may indeed be viewed as a form of social overhead capital.
A merit good is an economic concept; the human right is an ethical concept—and, sometimes, a legal concept. That said, the concept of a merit good and the judgment that a particular item is a merit good clearly have an ethical component. If one accepts the existence of a human right to water and sanitation, that could certainly motivate a government decision to make the provision of water and sanitation a merit good.
Even if a commodity is deemed to be a merit good, that still leaves open questions: To which group of people should it be provided as a merit good? In what quantity should it be provided? At what price, if any? By whom should it be provided? And how should the cost be funded?
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Infiltration of Water Into Soil
John Nimmo and Rose Shillito
The infiltration of water into soil has profound importance as a central component of the hydrologic cycle and as the means of replenishing soil water that sustains terrestrial life. Systematic quantitative study of infiltration began in the 19th century and has continued through to the present as a central topic of soils, soil physics, and hydrology. Two forces drive infiltration: gravity, and capillarity, which results from the interaction of air-water surface tension with the solid components of soil. There are also two primary ways water moves into and within the soil. One is diffuse flow, through the pores between individual soil grains, moving from one to the next and so on. The other is preferential flow, through elongated channels such as those left by worms and roots. Diffuse flow is slow and continues as long as there is a net driving force. Preferential flow is fast and occurs only when water is supplied at high intensity, as during irrigation, major rainstorms, or floods. Both types are important in infiltration. Especially considering that preferential flow does not yet have a fully accepted theory, this means that infiltration entails multiple processes, some of them poorly understood. The soil at a given location has a limit to how much water it can absorb—the infiltration capacity. The interplay between the mode and rate of water supply, infiltration capacity, and characteristics of the soil and surrounding terrain determines infiltration into the soil. Much effort has gone into developing means of measuring and predicting both infiltration capacity and the actual infiltration rate. Various methods are available, and research is needed to improve their accuracy and ease of use.
Article
Food Sovereignty
Mieke van Hemert
Food sovereignty is a paradigm on food system transformation advanced by peasant organizations worldwide in response to the commoditization of food through free trade agreements, deteriorating environmental and livelihood conditions in rural areas, and marginalization of the peasantry. Food sovereignty is an alternative to the current global, industrial corporate food regime and involves changes at all levels of the food system with relocalization, regaining control over territories, and agroecological production as key strivings. Food is viewed as a basic human right, as opposed to a commodity. Domestic consumption and food self-sufficiency have priority over long-distance trade. Food is regarded as a part of culture, heritage, and cosmovision. Agroecological practices that restore agrobiodiversity and lessen dependence and indebtedness of farmers are to replace monocultures, which are highly dependent on external inputs and harmful to the environment. There is a central role for smallholders and rural peoples in food production, who should (re)gain control over land and territories, individually and collectively, especially women. This is to be realized through forms of agrarian reform that go beyond land redistribution. Societal change toward peaceful coexistence, equality, and care for the earth is an ultimate goal.
Food sovereignty is a research topic in a wide range of disciplines, including sociology, anthropology, geography, law, philosophy, history, agronomy, and ecology, alongside transdisciplinary research on food systems. While first advanced as a mobilizing concept by the transnational agrarian movement La Vía Campesina in 1996, food sovereignty has become a policy framework adopted by various governments and international organizations. The movement has successfully lobbied the United Nations and the Food and Agriculture Organization to adopt new rights and guidelines that bring obligations for governments to protect rural peoples against transnational corporations undermining their access to land, water, forests, and seeds. The movement itself has diversified, and its definition of food sovereignty has evolved and become more inclusive.
The food sovereignty paradigm has been criticized for being too expansive, complex, and unclear. Analyses of the competing discourses of food sovereignty and food security reveal contrasts and complementarities. Scholarly debate has also focused on the position of both peasants and farm workers in the capitalist economy and on processes of de- and repeasantization.
Societal and scholarly debate on the various dimensions of food sovereignty is ongoing. Academic research foregrounds fundamental questions, including what role the state is expected to play, what forms of trade are envisaged, how the rights approach functions, the interplay of different transformative processes, changing economic and ecological contexts, tensions between different social groups, and power-related challenges. The number of case studies on the struggle for food sovereignty is growing and exhibits wide geographical diversity.
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Water User Associations and Collective Action in Irrigation and Drainage
Bryan Bruns
If there is too little or too much water, farmers may be able to work together to control water and grow more food. Even before the rise of cities and states, people living in ancient settlements cooperated to create better growing conditions for useful plants and animals by diverting, retaining, or draining water. Local collective action by farmers continued to play a major role in managing water for agriculture, including in later times and places when rulers sometimes also organized construction of dams, dikes, and canals.
Comparative research on long-lasting irrigation communities and local governance of natural resources has found immense diversity in management rules tailored to the variety of local conditions. Within this diversity, Elinor Ostrom identified shared principles of institutional design: clear social and physical boundaries; fit between rules and local conditions, including proportionality in sharing costs and benefits; user participation in modifying rules; monitoring by users or those accountable to them; graduated sanctions to enforce rules; low-cost conflict resolution; government tolerance or support for self-governance; and nested organizations.
During the 19th and 20th centuries, centralized bureaucracies constructed many large irrigation schemes. Farmers were typically expected to handle local operation and maintenance and comply with centralized management. Postcolonial international development finance for irrigation and drainage systems usually flowed through national bureaucracies, strengthening top-down control of infrastructure and water management.
Pilot projects in the 1970s in the Philippines and Sri Lanka inspired internationally funded efforts to promote participatory irrigation management in many countries. More ambitious reforms for transfer of irrigation management to water user associations (WUAs) drew on examples in Colombia, Mexico, Turkey, and elsewhere. These reforms have shown the feasibility in some cases of changing policies and practices to involve irrigators more closely in decisions about design, construction, and some aspects of operation and maintenance, including cooperation in scheme-level co-management. However, WUAs and associated institutional reforms are clearly not panaceas and have diverse results depending on context and on contingencies of implementation. Areas of mixed or limited impact and for potential improvement include performance in delivering water; maintaining infrastructure; mobilizing local resources; sustaining organizations after project interventions; and enhancing social inclusion and equity in terms of multiple uses of water, gender, age, ethnicity, poverty, land tenure, and other social differences.
Cooperation in managing water for agriculture can contribute to coping with present and future challenges, including growing more food to meet rising demand; competition for water between agriculture, industry, cities, and the environment; increasing drought, flood, and temperatures due to climate change; social and economic shifts in rural areas, including outmigration and diversification of livelihoods; and the pursuit of environmental sustainability.
Article
Crop Rotation and Climate Change Adaptation in Argentina’s Agriculture Sector
Ariel R. Angeli, Federico E. Bert, Sandro Díez-Amigo, Yuri Soares, Jaquelina M. Chaij, Gustavo D. Martini, F. Martín Montané, Alejandro Pardo Vegezzi, and Federico Schmidt
During the past two decades, extensive agriculture, particularly soybean production, has progressively replaced other crops in Argentina. This transformation was driven by economic, technological, environmental, and organizational factors, such as the increasing demand for agricultural commodities, technological advances, organizational innovations, and climate fluctuations. The expansion of soybean production has brought a substantial increase in agricultural revenue for Argentina. However, the predominance of soybean cultivation poses significant challenges, such as diminished soil fertility, reduction and increased variability in crop yields, ecological imbalance, increased greenhouse gas (GHG) emissions, and vulnerability to climate change.
Crop rotation, particularly balanced crop rotation, may result in very large positive impacts on soybean yields, especially in unfavorable climatic conditions such as those experienced during the La Niña ENSO phase in Argentina. In addition to this positive impact on agricultural productivity and climate adaptation, in some contexts crop rotation may also contribute to the reduction of GHG emissions, increased input energy efficiency, and improved environmental outcomes.
The 2018 Argentinian Association of Regional Consortia for Agricultural Experimentation and Inter-American Development Bank (AACREA-IADB) Integrated Crop Rotation Database compiled and harmonized the information from agricultural diaries kept by Regional Consortia for Agricultural Experimentation (CREA) members in Argentina from 1998 to 2016. This new consolidated data set has replaced previous regional templates, and it is expected to continue to be expanded with new information periodically, offering opportunities for further research on the impact of crop rotation on climate adaptation and on other topics in agricultural and environmental economics.
Article
Bioeconomic Models
Ihtiyor Bobojonov
Bioeconomic models are analytical tools that integrate biophysical and economic models. These models allow for analysis of the biological and economic changes caused by human activities. The biophysical and economic components of these models are developed based on historical observations or theoretical relations. Technically these models may have various levels of complexity in terms of equation systems considered in the model, modeling activities, and programming languages. Often, biophysical components of the models include crop or hydrological models. The core economic components of these models are optimization or simulation models established according to neoclassical economic theories. The models are often developed at farm, country, and global scales, and are used in various fields, including agriculture, fisheries, forestry, and environmental sectors. Bioeconomic models are commonly used in research on environmental externalities associated with policy reforms and technological modernization, including climate change impact analysis, and also explore the negative consequences of global warming. A large number of studies and reports on bioeconomic models exist, yet there is a lack of studies describing the multiple uses of these models across different disciplines.