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In Soviet Central Asia, efforts at the mass collectivization of agriculture began in early 1930, and by 1935, more than 80 percent of all farming and herding households joined collective farms (kolkhoz) or state farms (sovkhoz). The Communist Party’s main purpose was to control peasant lives and labor. Collectivization was supposed to lead to increased agricultural production due to modernized methods and intensification. The USSR’s Central Asian republics were given unachievable plans to raise their output of cotton, wheat, and meat, while wealthier herders and peasants were threatened with arrest and exile if they resisted collectivization. Collectivization was devastating for Kazakh nomadic herders, whose livestock numbers plummeted, and who endured a three-year long famine that killed more than one-fourth of the Kazakh population. Investments went into expanding irrigation canals and irrigable fields, forcing an ever-increasing number of kolkhoz members to expend most of their labor on cotton cultivation.

Water relations are gendered, and there are various, differential socio-ecological and power dynamics that reify those relations at different spatial scales. There are multiple examples across the Global North and Global South that pinpoint the diverse productive and reproductive uses of water by men and women. Women, for instance, are more likely to be excluded from water management and decision making, while men are in control of water for agricultural production. Neoliberal framings of water in economic terms may exacerbate gender inequalities as neoliberal policies are often blind to the complex politics and power embedded in gender relations and water. Emerging literature on embodiment and emotions in waterscapes confronts neoliberal framings of water by theorizing the everyday lived experience of disenfranchised groups excluded from water management. Gendered studies of water relations focus largely on women, with limited attention to men. Male usage of water is often presented in relation to their role in water infrastructure management and design and water for leisure. As climate change becomes a more pressing issue in general society, existing uneven gendered relations of water resource use will be further exacerbated. With prevalent literature on gender relations focusing on women, future research needs to further incorporate studies of masculinity in gender relations to better inform adaptation and mitigation strategies. An understanding of gender and education would be insufficient without an understanding of both gender differentials in access to water and the gendered implications of climate change.

Flowing through the North China Plain, one of China’s major agricultural regions, the Yellow River has long represented a challenge to Chinese governments to manage. Preventing floods has been an overriding concern for these states in order to maintain a semblance of ecological equilibrium on the North China Plain. This region’s environment is heavily influenced by seasonal fluctuations in precipitation, leading to a long history of famine, particularly in the late 19th and early 20th centuries when water management structures disintegrated with the deterioration of the imperial system. In the 20th century, new civil and hydraulic engineering techniques and technologies held the promise for enhanced management of the region’s waterways. After 1949, the new government of the People’s Republic used a hybrid approach consisting of the tenets of multipurpose water management combined with the tools of mass mobilization that were hallmarks of the Chinese Communist Party. The wide-ranging exploitation of surface and groundwater resources during the Maoist period left a long shadow for the post-Mao period that witnessed rapid consumption of water to fuel agricultural, industrial, and urban reforms. The challenge for the contemporary state in China is creating a system of water allocation through increased supply and demand management that can sustain the economic and social transformations of the era.

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.

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.

The Indus is the westernmost of the great arc of rivers across southern and eastern Asia flowing from the Tibetan plateau, and its watershed today includes parts of China, Afghanistan, Pakistan, and India. Flowing through a predominantly arid region, it was the site of South Asia’s earliest urban civilization in the 3rd millennium bce. Today, it features some of the most highly developed irrigation works in the world, supporting large agricultural populations on the plains of Pakistan and in northwestern India. Its history has been defined not only by the dynamics of the Indus river system, with its highly seasonal, monsoon-fed flows descending from the mountains, but also by its critical role in defining a transitional zone of migration and mobility situated between central Asia and the Iranian plateau, on the one hand, and the wetter parts of the Indian subcontinent, on the other. Within this context, it played a critical role in the coming of Islam to the subcontinent from the west. Since the late 19th century it has been the site of one of the modern world’s most dramatic irrigation-based transformations, rooted in British colonial canal-building and the opening of large canal colonies for agricultural settlement. What was already the world’s largest, integrated irrigation system was divided between India and Pakistan in 1947 (with the larger part going to Pakistan). The subsequent Indus Waters Treaty of 1960, which was intended to facilitate the continuing management of the river basin, accomplished this only through the intensification of irrigation investment and the maximization of the available water’s “use,” with all the difficult environmental and political challenges that has brought.

The vast region known as “Soviet Central Asia” encompassed the territory of five Soviet republics, Kazakhstan, Kirgizia, Uzbekistan, Tajikistan, and Turkmenistan. Because of the region’s environmental features, particularly its aridity, historically there had been a close linkage between people and the environment in this region. But the Soviet regime set out to radically reshape this relationship, focusing on the fields of agriculture and animal husbandry, large-scale water engineering, nuclear and biological weapons testing, and medicine and public health. By focusing on the environmental impact of these policies, scholars can see how Moscow’s efforts brought many benefits to the region. Cotton production boomed, and Moscow declared the eradication of malaria. But they also left horrific scars. Josef Stalin’s program of agricultural collectivization devastated Kazakhstan, resulting in the death of more than 1.5 million people. The Aral Sea, once one of the world’s largest bodies of water, began to shrink dramatically during the Soviet era, a development due in large part to Moscow’s efforts to divert the waters that fed the sea to cotton production.

East Africa is among the most environmentally diverse regions of the continent, and this diversity is reflected in its hydrology. The steppe plains, home to much of the region’s great wildlife, are defined by scarcity of rainfall and surface water resources. Within this sea of aridity, mountain peaks such as Kilimanjaro, Kenya, and Meru induce large amounts of rainfall and give rise to rivers that reach out into the grasslands. To the west, the forest–savannah mosaic and the shorelines of the Great Lakes likewise feature plentiful precipitation and surface water, giving rise to abundant vegetation and marine life. The Indian Ocean coast falls between in terms of rain, but its fate has been shaped by oceanic trade. In short, East Africa is a hydrological mosaic that has long influenced the social, cultural, and economic diversity of its human populations. The peoples of East Africa have long depended on the region’s water resources for their livelihoods. They have made sense of the region’s waterscapes, and developed strategies to manage them, in ways that reflected their own needs. Water management consisted not just of hydrological and technological expertise, but also cultural, spiritual, and political expertise. These in turn shaped economic as well as social relationships and hierarchies. With the onset of European colonization in the 19th and 20th centuries, water management became a focal point of struggles between local communities and various colonial actors—government officers, scientists, missionaries, and settlers—who developed very different impressions of the region’s waterscapes. These struggles involved not only conflict over the physical control of water resources, but also debates over what constituted useful and relevant water-management knowledge. Colonial actors described their water management in terms of science and modernity, while existing knowledge and practice were framed as primitive, wasteful, and destructive. Over the 20th century, conflicts intensified as users, African as well as European, demanded larger shares of increasingly scarce water resources. The post-colonial period did not spell an end to these struggles. Since the late 20th century, water management has emerged as a key aspect of national strategies for economic and social development. Yet decades of emphasis and millions of dollars spent have not led to sufficient progress in providing water to everyday people. Today, millions of East Africans lack access to clean, reliable water, a problem that is likely to worsen in the future.

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.

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.

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.

The period from the 1920s to the end of colonial rule saw increasing government intervention in agricultural production and the adoption of ambitious agricultural development schemes. These development schemes often aimed to increase and control the production and marketing of cash crops such as cotton and peanuts, essential to European industries. Examples include the Gezira Scheme (Sudan), the Office du Niger (French Soudan), the Tanganyika Groundnut Scheme, the Compagnie Générale des Oléagineux Tropicaux (CGOT, Senegal), as well as a host of other schemes. Confident in their agricultural expertise, colonial planners often sought radical transformations in African agricultural systems, away from extensive hoe cultivation toward intensive plow agriculture following a strict crop rotation. Worries about environmental degradation and population growth, as well as the need to manage social dislocation and maintain political stability, framed colonial strategies. Encountering African farmers with priorities and practices that were often at odds with their own, colonial planners failed to transform agriculture in the ways they intended. Nonetheless, development still wrought significant change as farmers considered whether to circumvent, resist, adapt, or adopt new technologies and farming methods. If at first agricultural development schemes were localized and mostly ineffective efforts to make empire profitable, by the 1940s and 1950s, agricultural development interventions became more widespread and intrusive. This helped generate rural support for anticolonial movements. Nonetheless, by the last decades of colonial rule, the idea of planned development as desirable became commonplace, not just within colonial governments, but also in international institutions and among nationalist leaders. Thus, state-led agricultural development would remain a powerful force in independent Africa.

Trade in the Sahara is as old as its current human occupation. The many different and often highly specialized ways in which Saharans have pursued their livelihoods since the region developed its current hyper-aridity roughly three thousand years ago, from settled agriculture to pastoral nomadism via intermediate forms, all fundamentally rely on mobility and exchange over short, medium, and long distances. Oases were established to facilitate trade, but they could not survive without sustained exchange with pastoral and trading economies. Pastoral nomads relied on sedentary outlets in their economic and migratory cycles. This simple observation has several implications for trans-Saharan trade: One, although historical periods can be identified when trans-Saharan trade visibly increased, in particular areas and for historically specific reasons, it is difficult and probably counterproductive to search for the origins of trans-Saharan trade as such. Two, the kind of trade that is most familiar from Arabic and European sources—namely, the trade in trans-Saharan luxuries—was only the tip of the iceberg of more stable patterns of exchange, much of which concerned rather mundane staples such as cereals, salt, and dates. The decline of visible, trans-Saharan trade at any particular moment and in any particular place hence does not imply the decline of all forms of Saharan trade. Three, thinking needs to extend beyond north–south axes, so that patterns of connectivity—which might just as easily stretch east or west—can be analyzed in their own terms. Four, all trade should not be assumed as necessarily trans-Saharan, that is to say, carrying goods produced beyond the Sahara across it to the other side, but Saharan production and consumption, also with regards to the enslaved, need to be taken into account. In turn, this means that Saharan trade should not be conceived of as in any way external to Saharan societies but as part and parcel of broader political, social, and economic logics, where calculations of material profits were not always the main driving force. Kin ties and marital alliances, and hence women, played major parts in this. Much of this is still true today, allowing transregional practice of exchange to continue in new forms, despite profound technological changes—from camel caravans to trucks—and the contemporary economic and political weight of postcolonial nation-states and their borders throughout the region. The current criminalization of all trans-Saharan activities, mostly through foreign military or diplomatic intervention, therefore cannot but have disastrous consequences for the region as a whole.

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.

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.

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.

Agrarian societies in Latin America and the Caribbean have accomplished some of the most important and influential innovations in agricultural knowledge and practice in world history—both ancient and modern. These enabled indigenous civilizations in Mesoamerica and the Andes to attain some of the highest population densities and levels of cultural accomplishment of the premodern world. During the colonial era, produce from the region’s haciendas, plantations, and smallholdings provided an essential ecological underpinning for the development of the world’s first truly global networks of trade. From the 18th to the early 20th century, the transnational activities of agricultural improvers helped turn the region into one of the world’s primary exporters of agricultural commodities. This was one of the most tangible outcomes of the Enlightenment and early state-building efforts in the hemisphere. During the second half of the 20th century, the region provided a prime testing ground for input-intensive farming practices associated with the Green Revolution, which developed in close relation with import-substituting industrialization and technocratic forms of governance. The ability of farmers and ranchers to intensify production from the land using new cultivars, technologies, and techniques was critical to all of these accomplishments, but often occurred at the cost of irreversible environmental transformation and violent social conflict. Manure was often central to these histories of intensification because of its importance to the cycling of nutrients. The history of the extraction and use of guano as a fertilizer profoundly shaped the globalization of input-intensive agricultural practices around the globe, and exemplifies often-overlooked connectivities reaching across regional boundaries and between terrestrial and aquatic environments.

The semi-arid interior of Brazil’s northeast region, known as the sertão, has long been subject to droughts. These can devastate the agricultural and ranching economy and cause serious hardship for the area’s inhabitants, particularly those who labor on farms and ranches belonging to the landowning elite. A prolonged drought in the late 1870s led the Brazilian government to begin soliciting advice from engineers about how to redress the periodic crisis. In 1909 the federal government established a permanent federal agency, the Inspectorate for Works to Combat Drought, to undertake reservoir construction throughout the sertão along with other measures that would alleviate future droughts. In subsequent decades the activities of the drought agency expanded to include constructing irrigation networks around reservoirs and establishing agricultural experiment stations to teach sertanejo farmers improved methods of farming in semi-arid conditions. Although powerful landowners lobbied for federal aid to construct reservoirs, which helped to sustain their own cattle herds through drought years, they were often opposed to initiatives like the establishment of irrigated smallholder colonies around reservoirs, which threatened to alter the social order in the sertão. Support for the federal drought agency’s work waxed and waned during the 20th century under different presidential administrations. Often it would rise in response to a period of damaging drought, then diminish once the crisis abated. Droughts have affected the sertão at irregular intervals since at least the colonial era. They vary in temporal duration and geographic expanse. Their impact on human populations depends on how the area of reduced rainfall overlaps with human settlement patterns and land use. Over the 20th century the years in which drought most severely impacted human communities (including crops and livestock) in the sertão included 1915, 1919–1920, 1931–1932, 1942, 1951–1953, 1958, 1970, 1979–1983, and 1998–1999. These are the periods when local, state, and federal governments received the most persistent pleas for assistance from affected populations. The precise cause of droughts in the region is debated, but they are thought to be triggered by changes in major wind patterns, particularly the El Niño Southern Oscillation (ENSO), that prevent Atlantic Ocean precipitation from reaching the sertão.

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.