Center-pivot irrigation systems started in the United States in the mid-20th century as an irrigation method which surpassed the traditional surface irrigation methods. At that time, they had the potential to bring about higher irrigation efficiencies with less water consumption although their requirements in energy were higher too. Among their benefits, it is highlighted the feasibility to control water management as well as the application of agro-chemicals dissolved in the irrigation water and thus, center-pivot irrigation systems have spread worldwide. Nevertheless, since the last decade of the 20th century, they are facing actual concerns regarding ecosystem sustainability and water and energy efficiencies. Likewise, the 21st century has brought about the cutting edge issue “precision irrigation” which has made feasible the application of water, fertilizers, and chemicals as the plant demands taking into account variables such as: sprinkler´s pressure, terrain topography, soil variability, and climatic conditions. Likewise, it could be adopted to deal with the current key issues regarding the sustainability and efficiency of the center-pivot irrigation to maintain the agro-ecosystems but still, other issues such as the organic matter incorporation are far to be understood and they will need further studies.
Article
Luis S. Pereira and José M. Gonçalves
Surface irrigation is the oldest and most widely used irrigation method, more than 83% of the world’s irrigated area. It comprises traditional systems, developed over millennia, and modern systems with mechanized and often automated water application and adopting precise land-leveling. It adapts well to non-sloping conditions, low to medium soil infiltration characteristics, most crops, and crop mechanization as well as environmental conditions. Modern methods provide for water and energy saving, control of environmental impacts, labor saving, and cropping economic success, thus for competing with pressurized irrigation methods. Surface irrigation refers to a variety of gravity application of the irrigation water, which infiltrates into the soil while flowing over the field surface. The ways and timings of how water flows over the field and infiltrates the soil determine the irrigation phases—advance, maintenance or ponding, depletion, and recession—which vary with the irrigation method, namely paddy basin, leveled basin, border and furrow irrigation, generally used for field crops, and wild flooding and water spreading from contour ditches, used for pasture lands. System performance is commonly assessed using the distribution uniformity indicator, while management performance is assessed with the application efficiency or the beneficial water use fraction. The factors influencing system performance are multiple and interacting—inflow rate, field length and shape, soil hydraulics roughness, field slope, soil infiltration rate, and cutoff time—while management performance, in addition to these factors, depends upon the soil water deficit at time of irrigation, thus on the way farmers are able to manage irrigation. The process of surface irrigation is complex to describe because it combines surface flow with infiltration into the soil profile. Numerous mathematical computer models have therefore been developed for its simulation, aimed at both design adopting a target performance and field evaluation of actual performance. The use of models in design allows taking into consideration the factors referred to before and, when adopting any type of decision support system or multicriteria analysis, also taking into consideration economic and environmental constraints and issues.
There are various aspects favoring and limiting the adoption of surface irrigation. Favorable aspects include the simplicity of its adoption at farm in flat lands with low infiltration rates, namely when water conveyance and distribution are performed with canal and/or low-pressure pipe systems, low capital investment, and low energy consumption. Most significant limitations include high soil infiltration and high variability of infiltration throughout the field, land leveling requirements, need for control of a constant inflow rate, difficulties in matching irrigation time duration with soil water deficit at time of irrigation, and difficult access to equipment for mechanized and automated water application and distribution. The modernization of surface irrigation systems and design models, as well as models and tools usable to support surface irrigation management, have significantly impacted water use and productivity, and thus competitiveness of surface irrigation.
Article
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
Deborah L. Nichols
The Basin of Mexico is a key world region for understanding agricultural intensification and the development of ancient and historic cities and states. Archaeologists working in the region have had a long-standing interest in understanding the dynamics of interactions between society and environment and their research has been at the forefront of advances in both method and theory. The Basin of Mexico was the geopolitical core of the Aztec empire, the largest state in the history of Mesoamerica. Its growth was sustained by a complex economy that has been the subject of much research.
Two themes underlie a broad interest in the pre-Hispanic agriculture of the Basin of Mexico. First, how with a Neolithic technology did the Aztecs and their predecessors sustain the growth of large cites, dense rural populations, and the largest state system in the history of pre-Hispanic Mesoamerica? Second, what is the relationship of agricultural intensification and urbanization and state formation? Mesoamerica is the only world region where primary civilizations developed that lacked domestic herbivores for either food or transportation. Their farming depended entirely on human labor and hand tools but sustained large cities, dense populations, and complex social institutions. Intensive agriculture began early and was promoted by risk, ecological diversity, and social differentiation, and included irrigation, terracing, and drained fields (chinampas). Most farming was managed by smallholder households and local communities, which encouraged corporate forms of governance and collective action. Environmental impacts included erosion and deposition, but were limited compared with the degradation that took place in the colonial period.
Article
Soil salinity has been causing problems for agriculturists for millennia, primarily in irrigated lands. The importance of salinity issues is increasing, since large areas are affected by irrigation-induced salt accumulation. A wide knowledge base has been collected to better understand the major processes of salt accumulation and choose the right method of mitigation. There are two major types of soil salinity that are distinguished because of different properties and mitigation requirements. The first is caused mostly by the large salt concentration and is called saline soil, typically corresponding to Solonchak soils. The second is caused mainly by the dominance of sodium in the soil solution or on the soil exchange complex. This latter type is called “sodic” soil, corresponding to Solonetz soils. Saline soils have homogeneous soil profiles with relatively good soil structure, and their appropriate mitigation measure is leaching. Naturally sodic soils have markedly different horizons and unfavorable physical properties, such as low permeability, swelling, plasticity when wet, and hardness when dry, and their limitation for agriculture is mitigated typically by applying gypsum. Salinity and sodicity need to be chemically quantified before deciding on the proper management strategy. The most complex management and mitigation of salinized irrigated lands involves modern engineering including calculations of irrigation water rates and reclamation materials, provisions for drainage, and drainage disposal. Mapping-oriented soil classification was developed for naturally saline and sodic soils and inherited the first soil categories introduced more than a century ago, such as Solonchak and Solonetz in most of the total of 24 soil classification systems used currently. USDA Soil Taxonomy is one exception, which uses names composed of formative elements.
Article
Encarna Esteban
The increased pressure on groundwater has resulted in a major deterioration of the overall status of this resource. Despite efforts to control the degradation of underground water bodies, most aquifers worldwide experience serious quality and quantity problems. New emerging issues around groundwater resources have become relevant and pose additional protection and management challenges. Climate change, with predictable impacts on temperature and precipitation, will cause considerable fluctuations in aquifer recharge levels and subsequent problems in the status of these water bodies. Expected reductions in water availability will increase groundwater withdrawals not just for irrigation but also for urban and industrial water use. Declines in stored water will have an impact on many freshwater ecosystems whose survival depends on the status of groundwater bodies. Furthermore, land subsidence, as a side effect of aquifer overexploitation, involves land collapse and deformation that are especially harmful for urban areas and deteriorate physical and hydrological water systems. All these new challenges require integrated planning strategies and multisectorial solutions to curtail the deterioration of these resources. Although these issues have been studied, in-depth analyses of the economic, social, and policy implications of groundwater management strategies are still necessary.
Article
Renata Rimšaitė and Nicholas Brozović
The High Plains Aquifer is the largest aquifer in the United States and the major source of groundwater withdrawals in the region. Although regionally abundant, groundwater availability for agriculture and other uses is not uniform across the area. Three separate states comprising the most significant portion of the aquifer have distinct climate and hydrologic characteristics, water law systems, and institutional groundwater governance leading to different concerns about water policy issues across the area.
The northern, largest, and most saturated part of the High Plains Aquifer is located under Nebraska. The state has the largest irrigated area in the United States, most of which is groundwater irrigated. Nebraska is the home of the largest companies in the center pivot irrigation industry. Center pivot technology has had a fundamental role in expanding groundwater-fed irrigation. Nebraska is not free from groundwater depletion issues, but these issues are more important in central and south-central parts of the aquifer underlying large, primarily agricultural, lands of Kansas and Texas. The natural aquifer recharge is much lower in the south-central parts of the region, which has caused large groundwater extractions to have more significant water declines than in Nebraska.
In the United States, the greatest portion of water quantity management regulatory oversight is left to individual states and local government agencies. Each of the three states has a unique legal system, which highly influences the framework of groundwater management locally. In Nebraska, groundwater is governed following two doctrines: correlative and reasonable use, which, in times of water shortage, lead to a proportional reduction of everyone’s allocation. Kansas uses the prior appropriation doctrine to manage groundwater, which applies the seniority principle when there is scarcity in water availability, making junior water rights holders bear the greatest risk. The absolute ownership doctrine is used to govern groundwater in Texas, which allows landowners to drill wells on their property and extract as much water as needed.
Institutional groundwater governance in Nebraska is performed by the system of 25 locally elected Natural Resources Districts having full regulatory power to manage the state’s groundwater. The local governments use a variety of regulatory and incentive-based groundwater management tools to achieve local groundwater management goals. In Kansas, the Chief Engineer in the Kansas Department of Agriculture is in charge of water administration for the state. The Kansas legislature established five Groundwater Management Districts to address groundwater depletion issues, which can make policy recommendations but do not have the power to regulate. Groundwater Conservation Districts were created in Texas to provide protection from uncontrolled water mining in the state. The districts gained more power to regulate and enforce rules over time; however, significant groundwater depletion issues remain.
Multiple lessons have been learned across the region since the beginning of groundwater development. Some of these could be applied in other areas seeking to address negative consequences of groundwater use. Forward-looking perspectives about groundwater management in the region vary from strong government-led solutions in Nebraska to various producer-initiated innovative approaches in Kansas and Texas.
Article
Noa Kekuewa Lincoln and Peter Vitousek
Agriculture in Hawaiʻi was developed in response to the high spatial heterogeneity of climate and landscape of the archipelago, resulting in a broad range of agricultural strategies. Over time, highly intensive irrigated and rainfed systems emerged, supplemented by extensive use of more marginal lands that supported considerable populations. Due to the late colonization of the islands, the pathways of development are fairly well reconstructed in Hawaiʻi. The earliest agricultural developments took advantage of highly fertile areas with abundant freshwater, utilizing relatively simple techniques such as gardening and shifting cultivation. Over time, investments into land-based infrastructure led to the emergence of irrigated pondfield agriculture found elsewhere in Polynesia. This agricultural form was confined by climatic and geomorphological parameters, and typically occurred in wetter, older landscapes that had developed deep river valleys and alluvial plains. Once initiated, these wetland systems saw regular, continuous development and redevelopment. As populations expanded into areas unable to support irrigated agriculture, highly diverse rainfed agricultural systems emerged that were adapted to local environmental and climatic variables. Development of simple infrastructure over vast areas created intensive rainfed agricultural systems that were unique in Polynesia. Intensification of rainfed agriculture was confined to areas of naturally occurring soil fertility that typically occurred in drier and younger landscapes in the southern end of the archipelago. Both irrigated and rainfed agricultural areas applied supplementary agricultural strategies in surrounding areas such as agroforestry, home gardens, and built soils. Differences in yield, labor, surplus, and resilience of agricultural forms helped shape differentiated political economies, hierarchies, and motivations that played a key role in the development of sociopolitical complexity in the islands.
Article
Reiner Wassmann
Assessing the environmental footprints of modern agriculture requires a balanced approach that sets the obviously negative effects (e.g., incidents with excessive use of inputs) against benefits stemming from increased resource use efficiencies. In the case of rice production, the regular flooding of fields comprises a distinctive feature, as compared to other crops, which directly or indirectly affects diverse impacts on the environment. In the regional context of Southeast Asia, rice production is characterized by dynamic changes in terms of crop management practices, so that environmental footprints can only be assessed from time-dependent developments rather than from a static view. The key for the Green Revolution in rice was the introduction of high-yielding varieties in combination with a sufficient water and nutrient supply as well as pest management. More recently, mechanization has evolved as a major trend in modern rice production. Mechanization has diverse environmental impacts and may also be instrumental in tackling the most drastic pollution source from rice production, namely, open field burning of straw. As modernization of rice production is imperative for future food supplies, there is scope for developing sustainable and high-yielding rice production systems by capitalizing on the positive aspects of modernization from a local to a global scale.
Article
Stefanos Xenarios, Murat Yakubov, Aziza Baubekova, Olzhas Alshagirov, Zhassulan Zhalgas, and Eduardo Jr Araral
Central Asia (CA) hosts some of the world’s most complex and most extensive water management infrastructures allocated in the two major transboundary basins of the Amudarya and Syrdarya Rivers. The upstream countries of Tajikistan and Kyrgyzstan mainly utilize the rivers for hydropower and irrigation, whereas the downstream countries of Uzbekistan, Turkmenistan, and Kazakhstan primarily use them for irrigation purposes. The governance of the two river basins has been contested since Soviet times, and more so after the independence of the CA countries. The scheme of Small Basin Councils (SBCs) has been introduced in the region from 2010 to 2022 to improve local and transboundary water governance at a sub-basin and catchment level. Implementing SBCs in CA is still in the experimental phase, and its contribution to river basin management is insufficiently explored. However, there are indications that SBCs play a significant role in raising awareness of and engagement with local communities and improving local and transboundary governance management and coordination. Most important, SBCs can help resolve critical issues in agricultural water allocation, one of the most contentious issues for transboundary water governance in CA. The basin councils could become significant leverage for improving water governance on national and transboundary systems in CA by actively engaging local communities in management, planning, and administration.
Article
Francesca Greco, Martin Keulertz, and David Dent
Virtual water is the water contained in food, understood not only as the physical amount within the product but also as the amount of water required to generate it over time, from planting to final harvest. Despite Tony Allan defined virtual water in the context of the water needed to produce agricultural commodities, the concept has been subsequently expanded to include the water needed to produce non-agricultural commodities and industrial goods by Arjen Hoekstra, the creator of the water footprint indicator. Virtual water is a revolutionary concept because it describes something never conceptualized before: the water “embedded” in a product. Allan used virtual water “food water” and “embedded water” as interchangeable terms. Virtual water “trade” is the result of food trade: where agricultural goods are traded across countries, the water needed to produce that product in country A is, in fact, consumed in country B. Country B is therefore not consuming its own local resources when consuming imported food. Allan believed that this mechanism could alleviate irrigation water needs in water-scarce areas when food imports are in place. The virtual water content of a product (measured in liters per kilo) is provided not only by the sum of the irrigation water that has been withdrawn from surface and underground sources in order to grow crops—called “blue water.” Virtual water is also composed of the rainwater consumed by plants and persisting in agricultural soil moisture, which does not percolate down to the aquifers or go back to rivers and lakes. This second component is called “green water.” The green- and blue-water components form the total amount of water embedded in crops, and they are the two components of virtual water. Allan borrowed the concepts of green and blue water from the work of Malin Falkenmark. Virtual water and virtual water “trade” have been largely explored and studied at both local and global levels, becoming the subjects of thousands of papers between 1993 and 2022, which helped uncover global appropriation of a local resource that is unevenly distributed by nature and very often unequally “traded” by humans: water.
Article
Gerrit de Rooij
Henry Darcy was an engineer who built the drinking water supply system of the French city of Dijon in the mid-19th century. In doing so, he developed an interest in the flow of water through sands, and, together with Charles Ritter, he experimented (in a hospital, for unclear reasons) with water flow in a vertical cylinder filled with different sands to determine the laws of flow of water through sand. The results were published in an appendix to Darcy’s report on his work on Dijon’s water supply. Darcy and Ritter installed mercury manometers at the bottom and near the top of the cylinder, and they observed that the water flux density through the sand was proportional to the difference between the mercury levels. After mercury levels are converted to equivalent water levels and recast in differential form, this relationship is known as Darcy’s Law, and until this day it is the cornerstone of the theory of water flow in porous media. The development of groundwater hydrology and soil water hydrology that originated with Darcy’s Law is tracked through seminal contributions over the past 160 years.
Darcy’s Law was quickly adopted for calculating groundwater flow, which blossomed after the introduction of a few very useful simplifying assumptions that permitted a host of analytical solutions to groundwater problems, including flows toward pumped drinking water wells and toward drain tubes. Computers have made possible ever more advanced numerical solutions based on Darcy’s Law, which have allowed tailor-made computations for specific areas. In soil hydrology, Darcy’s Law itself required modification to facilitate its application for different soil water contents. The understanding of the relationship between the potential energy of soil water and the soil water content emerged early in the 20th century. The mathematical formalization of the consequences for the flow rate and storage change of soil water was established in the 1930s, but only after the 1970s did computers become powerful enough to tackle unsaturated flows head-on. In combination with crop growth models, this allowed Darcy-based models to aid in the setup of irrigation practices and to optimize drainage designs. In the past decades, spatial variation of the hydraulic properties of aquifers and soils has been shown to affect the transfer of solutes from soils to groundwater and from groundwater to surface water. More recently, regional and continental-scale hydrology have been required to quantify the role of the terrestrial hydrological cycle in relation to climate change. Both developments may pose new areas of application, or show the limits of applicability, of a law derived from a few experiments on a cylinder filled with sand in the 1850s.
Article
Richard W. Hazlett and Joshua Peck
Satellite reconnaissance of the Earth’s surface provides critical information about the state of human interaction with the natural environment. The strongest impact is agricultural, reflecting land-use approaches to food production extending back to the dawn of civilization. To variable degrees, depending upon location, regional field patterns result from traditional farming practices, surveying methods, regional histories, policies, political agendas, environmental circumstances, and economic welfare. Satellite imaging in photographic true or false color is an important means of evaluating the nature and implications of agricultural practices and their impacts on the surrounding world. Important platforms with publicly accessible links to satellite image sets include those of the European Space Agency, U.S. National Aeronautics and Space Administration, the Centre D’etudes Spatiales, Airbus, and various other governmental programs. Reprocessing of data worldwide in scope by commercial concerns including Digital Globe, Terrametrics, and GoogleEarth in the 21st century enable ready examination of most of the Earth’s surface in great detail and natural colors. The potential for monitoring and improving understanding of agriculture and its role in the Earth system is considerable thanks to these new ways of viewing the planet.
Space reconnaissance starkly reveals the consequences of unique land surveys for the rapid development of agriculture and political control in wilderness areas, including the U.S. Public Land Survey and Tierras Bajas systems. Traditional approaches toward agriculture are clearly shown in ribbon farms, English enclosures and medieval field systems, and terracing in many parts of the world. Irrigation works, some thousands of years old, may be seen in floodplains and dryland areas, notably the Maghreb and the deep Sahara, where center-pivot fields have recently appeared in areas once considered too dry to cultivate. Approaches for controlling erosion, including buffer zones, shelter belts, strip and contour farming, can be easily identified. Also evident are features related to field erosion and soil alteration that have advanced to crisis stage, such as badland development and widespread salinization. Pollution related to farm runoff, and the piecemeal (if not rapid) loss of farmlands due to urbanization can be examined in ways favoring more comprehensive evaluation of human impacts on the planetary surface. Developments in space technologies and observational platforms will continue indefinitely, promising ever-increasing capacity to understand how humans relate to the environment.
Article
Marc Jeuland
Water resources represent an essential input to most human activities, but harnessing them requires significant infrastructure. Such water control allows populations to cope with stochastic water availability, preserving uses during droughts while protecting against the ravages of floods. Economic analysis is particularly valuable for helping to guide infrastructure investment choices, and for comparing the relative value of so called hard and soft (noninfrastructure) approaches to water management.
The historical evolution of the tools for conducting such economic analysis is considered. Given the multimillennial history of human reliance on water infrastructure, it may be surprising that economic assessments of its value are a relatively recent development. Owing to the need to justify the rapid deployment of major public-sector financing outlays for water infrastructure in the early 20th century, government agencies in the United States—the Army Corps of Engineers and the Bureau of Reclamation—were early pioneers in developing these applications. Their work faced numerous technical challenges, first addressed in the drafting of the cost-benefit norms of the “Green Book.” Subsequent methodological innovation then worked to address a suite of challenges related to nonmarket uses of water, stochastic hydrology, water systems interdependencies, the social opportunity cost of capital, and impacts on secondary markets, as well as endogenous sociocultural feedbacks. The improved methods that have emerged have now been applied extensively around the world, with applications increasingly focused on the Global South where the best infrastructure development opportunities remain today.
The dominant tools for carrying out such economic analyses are simulation or optimization hydroeconomic models (HEM), but there are also other options: economy wide water-economy models (WEMs), sociohydrological models (SHMs), spreadsheet-based partial equilibrium cost-benefit models, and others. Each of these has different strengths and weaknesses. Notable innovations are also discussed. For HEMs, these include stochastic, fuzz, and robust optimization, respectively, as well as co-integration with models of other sectors (e.g., energy systems models). Recent cutting-edge work with WEMs and spreadsheet-based CBA models, meanwhile, has focused on linking these tools with spatially resolved HEMs. SHMs have only seen limited application to infrastructure valuation problems but have been useful for illuminating the paradox of flood management infrastructure increasing the incidence and severity of flood damages, and for explaining the co-evolution of water-based development and environmental concerns, which ironically then devalues the original infrastructure. Other notable innovations are apparent in multicriteria decision analysis, and in game-theoretic modeling of noncooperative water institutions.
These advances notwithstanding, several issues continue to challenge accurate and helpful economic appraisal of water infrastructure and should be the subject of future investigations in this domain. These include better assessment of environmental and distributional impacts, incorporation of empirically based representations of costs and benefits, and greater attention to the opportunity costs of infrastructure. Existing tools are well evolved from those of a few decades ago, supported by enhancements in scientific understanding and computational power. Yet, they do appear to systematically produce inflated estimations of the net benefits of water infrastructure. Tackling existing shortcomings will require continued interdisciplinary collaboration between economists and scholars from other disciplines, to allow leveraging of new theoretical insights, empirical data analyses, and modeling innovations.
Article
William D. A. Bryant
General equilibrium theory thinks of the economy as a collection of interconnected markets, each of which, in isolation and in combination, is driven toward some sort of equilibrium. Computable general equilibrium (CGE) models add to this abstract point of view by calibrating models of the economy using actual economic data. The aim is to empirically solve for equilibrium demand, supply, and price levels across the markets in the economy. Many areas of economic analysis, reform, and policymaking have benefitted from scrutiny in a CGE context. This is particularly true of issues to do with tax and tariff reform, where CGE models first gained prominence. More recently, the areas of environmental economics and regulation has attracted the attention of CGE modelers. Considerations of environment and environmental regulation, inevitably involve a consideration of issues to do with water. Such issues range from aquaculture through pricing of water to virtual water—and many points in between. In the analysis of each of these issues—and the role water plays in the overall economy, CGE models have made an important contribution to understanding and informed policymaking.
