Is the Hydrologic Cycle Sustainable?

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Is the Hydrologic Cycle Sustainable?

A Historical–Geographical Critique of a Modern Concept

Jamie Linton, Department of Geography, Queen’s University

The hydrologic cycle is treated in this article as an invention that represents and helps structure a particular understanding of water. Ideas about the circulation of water in what is now called the hydrosphere have been discussed for millennia, and quantitative proof of the basic water balance (between evaporation, precipitation, and streamflow) was established by the nineteenth century. However, “the hydrologic cycle” as a distinct entity and the diagrammatic form by which it is typically represented are much more recent products of hydrological discourse. This article describes the gestation of this entity in the English-speaking hydrological tradition and explains how and why it attained a specific form in the United States in the 1930s. This modern hydrologic cycle, it is argued, internalizes the historical and geographical circumstances in which it was formed; namely a northern temperate society in the throes of modern, state-led industrial development. These circumstances, however, no longer pertain to a majority of people, whose experience of water is different from that represented in the standard hydrologic cycle. To the extent that it structures an understanding of water that is increasingly at odds with social and hydrological experience, the modern hydrologic cycle can be considered unsustainable.

Key Words: geography of science, historyof science, hydrologic cycle, hydrology, water.

The hydrologic cycle is the most fundamental principle of hydrology. Water evaporates from the oceans and the land surface, is carried over the Earth in atmospheric circulation as water vapor, precipitates again as rain or snow, is intercepted by trees and vegetation, provides runoff on the land surface, infiltrates into soils, recharges groundwater, discharges into streams, and ultimately, flows out into the oceans from which it will eventually evaporate once again.

This immense water engine, fuelled by solar energy, driven by gravity, proceeds endlessly in the presence or absence of human activity.

—Maidment 1993, 1.3

The water cycle is one of nature’s grand plans. It begins as rain, becomes lakes and streams seeking the sea, and is completed when water vapor, lifted by the sun from earth and oceans, falls again as rain.

—Langbein and Hoyt 1959, 3

The hydrologic cycle, also known as the water cycle and the hydrological cycle, is treated in this article as a highly successful invention. Attaining its modern form in hydrological discourse, the hydrologic cycle has spilled beyond the confines of academe and may now be said to flood the popular imagination. Most of the readers of this journal will have gained familiarity with its basic lineaments in primary school. A quick Internet search for images of the hydrologic, hydrological, or water cycle yields hundreds of illustrations and diagrams, even more than for another very common means of representing water—H2O. Like H2O, the ubiquity of the hydrologic cycle contributes to the invisibility of its invention, allowing it to “proceed endlessly in the presence or absence of human activity” as noted by Maidment (1993, 1.3). Other hydrologists have put the matter even more plainly: The hydrologic cycle is “one of nature’s grand plans” (Langbein and Hoyt 1959, 3), “the natural pattern of circulation of water” (Thomas 1956, 544), and “a great natural system” (Chorley and Kates 1969, 3).As natural(ized) as it has become, however, the hydrologic cycle nevertheless internalizes a human story. To the extent that a “grand plan” is involved, much of the planning has been on the side of the people who, quite literally, have drawn the hydrologic cycle from water’s ineffable flow.

The idea of the circulation of water on Earth is hardly new, having occurred in a variety of places and ways throughout the history of Western thought. The hydrologic cycle against which this critique is addressed differs from this venerable concept by having been given a name and a specific visual form, and by the presumption that these represent the universal (natural) disposition of water. It is this modern hydrologic cycle—the one that appears on classroom posters, in university textbooks, on the Internet, and in countless publications describing and depicting water in general terms—for which the genealogy is traced and the sustainability of which is questioned in this article. To be clear, by questioning the “sustainability” of the hydrologic cycle, I mean to draw attention to the adequacy of this means by which we know water rather than to comment on the state of water itself.

Standard histories in English of the hydrological sciences treat the hydrologic cycle as something that was sometimes intuited by (the more prescient) ancient sages, but required the application of proper scientific methods to become revealed as truth (cf.Meinzer 1942, 8–30; Jones et al. 1963; Parizek 1963; Biswas 1965, 1970; Kazman 1972, 5–21; Dooge 1974, 1988, 2001; Nace 1974, 1975). Accordingly, the scientific origins of the concept are usually situated in the quantitative investigations of natural philosophers experimenting in the late seventeeth century, during the period often described as the Scientific Revolution. The description of hydrology in the Dictionary of Physical Geography provides a standard reference:

The study of hydrology is at least as old as the ancient civilizations of Egypt, because the provision of a reliable water supply is essential to the survival of man. However, the development of plausible theories concerning the circulation of water in the hydrological cycle did not appear until the seventeenth century. These were largely based on observations of rainfall and river flow in the Seine basin by Pierre Perrault and Edme Mariotte and on the ideas of Edmond Halley who simulated evaporation from the Mediterranean and concluded that this could account for all surface drainage. (Goudie 2000, 256)

The approach taken in this article differs from the standard histories of hydrology in that it does not consider the hydrologic cycle as something immanent in nature and requiring the application of correct scientific method to be revealed. Rather, it treats the modern hydrologic cycle as a way of representing water that was constructed in, rather than revealed through, scientific practice. Thus the particular form that the hydrologic cycle gives to water is explained by way of historical reconstruction of its representation rather than by the investigation of the nature of water itself. Accordingly, I have located the origin of the (modern) hydrologic cycle in an entirely different set of historical circumstances from those with which it is usually associated. This relocation addresses one aim of the article, which is to explain why as well as how—the purposes for, as well as the means by which—the modern hydrologic cycle was established, and why it appears the way it does. In adopting this approach, I follow approximately the method described by historian of science Jan Golinsky, for whom a “constructivist outlook” is one that “regards scientific knowledge primarily as a human product, made with locally situated cultural and material resources, rather than as simply the revelation of a pre-given order of nature” (Golinski 1998, ix).

To speak of “locally situated . . . material resources” suggests another aim of the article, for although the hydrologic cycle has a definite history, it also internalizes a particular geography of water. The geographical particularities of the place(s) in which it was conceived imbue the hydrologic cycle with a certain bias; however this bias is concealed by its catholicity. “All water is involved in a continuous hydrologic cycle,” as one standard reference makes perfectly clear (Marsh 1985, 2279). The hydrologic cycle thus embraces all water, but it hardly treats all waters fairly: Its balance and symmetry, its even-tempered regard for evaporation, condensation, precipitation and runoff, is incongruous with the experience of water in deserts, polar regions, or places subject to pronounced hydrological variability (seasonal or annual fluctuations in precipitation). David Livingstone has shown the importance of “putting science in its place” in the sense of attending to the geography of the production of scientific knowledge: “There are always stories to be told of how scientific knowledge came to be made where and when it did. The appearance of universality that science enjoys, and its capacity to travel with remarkable efficiency across the surface of the earth, do not dissolve its local character” (Livingstone 2003, 14). Following Livingstone’s admonition, a second task of the article is to attend to the geography of the production of the hydrologic cycle, and to consider the implications of its presumed universality.

Considering the history and geography of the hydrologic cycle suggests another aim, or question, that I want to address in this article: If the hydrologic cycle is particular to a certain set of historical and geographical circumstances, how can it be sustained at a time when, perhaps more than ever, we need to consider the particularities of water’s various engagements with people? All the talk of the “global water crisis” beginning in the early 1990s belies a world of myriad, disparate, local challenges posed by the need to meld human activities with the realities of diverse contemporary waters (Linton 2006b). At the same time that the modern hydrologic cycle has structured our understanding of water’s nature, these various waters have had to adjust themselves to a single hydraulic paradigm that regards all water (and all people insofar as the way they relate to water) as fundamentally the same. The universality of the hydrologic cycle, useful as it may have been for the expert discourse of hydrosocial relations known as water management, is becoming unsustainable in the face of social and hydrological circumstances that call for heterogeneous relations with water.

The Circulation of Water and the Wisdom of God

At least since the time of Aristotle, philosophers and sages have discoursed on the behavior of water in what we now call the hydrosphere, offering an amusing variety of observations, explanations, and hypotheses of hydrological phenomena. The idea of the circulation of water on Earth is among the earliest conjectures of natural philosophy, with practically every writer in this category from antiquity to the nineteenth century offering views on the subject (Biswas 1965, 1970). Until the eighteenth century, however, the “dominant theory” held that the circulation of water was primarily a subterranean affair (Dooge 2001). As illustrated in Figure 1, the main source of water descending in streams and rivers from upland regions was thought to come directly from the sea via subterranean rivers and reservoirs.

Overturning the subterranean thesis and proving the “correct” hydrologic cycle is perhaps the central story told in the standard histories of modern hydrology. As illustrated in the earlier quote from the Dictionary of Physical Geography (Goudie 2000), quantitative investigations showing that precipitation (minus evaporation) could fully account for streamflow were made by the French proto-hydrologists Perrault and Mariotte in the mid-seventeenth century. Halley’s experiment, reported in 1687, showed that evaporation from the Mediterranean Sea was more than adequate to account for the combined inflow of its rivers. Halley thus “attempted to show a balance in the complete cycle of water movement” and for these efforts is judged, along with his French cohorts, to have established “the concept of the cycle” (Nace 1974, 46). The actual “proof by accurate measurement” of the hydrologic cycle, however, is considered to have been rendered by John Dalton in 1802, when he undertook the first regional water balance study (for England and Wales; Dooge 1974; Nace 1974).

Figure 1. Adepiction of the widely held notion of the subterranean source of springs and rivers, from Athanasius Kircher’s Mundus Subterraneus, ca. 1664. The subterranean flow of water (originating at the sea bottom) is shown in darkened channels. The cutaway view illustrates the common belief that water was channelled to reservoirs beneath mountains from which it sprang forth, giving rise to springs and rivers. Source: Adams (1938, 437).

To say that Perrault, Marriotte, Halley, and Dalton established the concept of the hydrologic cycle is something of an anachronism produced through a modern reading of their work. Only in light of subsequent events is it possible to look back and assemble the hydrologic cycle in the writings and thoughts of people for whom it did not yet exist. These writings and thoughts, however, did make an important contribution to a contemporaneous idea that is sometimes mistaken for the modern hydrologic cycle. The idea of the circulation of water was applied to the larger argument that brought the latest findings in natural philosophy to bear on the question of the existence and immanence of the Christian God. Natural theology (or physico-theology as it was also known) became most prominent in the seventeenth and eighteenth centuries, especially among English savants who sought to rekindle the sacred in a world they felt had been secularized at the hands of Cartesian mechanical philosophy. Essentially, this school of natural philosophy sought prove the existence of God by means of adducing evidence of a divine order—or design—in His Creation (Glacken 1967, 375–428; Livingstone 1992, 105–13).

Among the most stalwart arguments deployed in natural theology was the even distribution and constant cycling of water on the Earth’s surface. In a study published in 1968, Yi Fu Tuan detailed “the popularity and the almost constant exploitation of the concept of the hydrologic cycle [sic] in physico-theology” from the late seventeenth to the mid-nineteenth century (Tuan 1968, 122). Although embracing the subterranean hypothesis in the seventeenth century, natural theology quickly adopted the latest scientific findings by Halley and others, so that by 1701, the concept that was being purveyed resembles the modern hydrologic cycle. To cite an example (and the one with which Tuan begins his account), we can consider the English naturalist John Ray: In response to the question he puts in the mouths of doubters and atheists (“Where is the Wisdom of the Creator in making so much useless sea, and so little dry land?”), Ray replies with a disquisition on the circulation of water:

This, as most other of the Atheists Arguments, proceeds from a deep Ignorance of Natural Philosophy; for if there were but half the Sea that now is, there would be also but half the Quantity of Vapours, and consequently we could have but half so many Rivers as now there are to supply all the dry land we have at present, and half as much more; for the quantity of Vapours which are rais’d, bears a Proportion to the surface whence they are rais’d, as well as to the heat which rais’d them. The Wise Creator therefore did so prudently order it, that the Sea should be large enough to supply Vapours sufficient for all the Land, which it would not do if it were less than now it is. ( quoted in Tuan 1968, 10; italics added)

The notion that “all the land” was well supplied with water was not unique to Ray. Whether out of ignorance or out of enthusiasm, the geographical fact of aridity was conveniently overlooked by proponents of what might be called the “sacred” hydrologic cycle. From Ray on down to “the many reputable authors in the first half of the nineteenth century who trotted out the same concept and seldom bothered even to vary the rhetoric” the hydrologic cycle both reflected and effected a kind of faith in the universality of humidity (Tuan 1968, 133). By 1900, the sacred hydrologic cycle had nearly stopped flowing. The growing influence of Darwinism meant that the wonders of nature could less easily be attributed to a divine architect, but now required an explanation that accorded with the internal logic of nature itself (Tuan 1968, 149). The cyclic character of earthly processes, established in modern discourse with Hutton’s Geological Cycle, had become something of a staple of the budding earth sciences by the late nineteenth century (Hettner [1928] 1972, 104; Kennedy 2006, 31– 32). The circulation of water thus left its sacred course and was channelled through more secular, scientific language. Nevertheless some sense of the magnanimity and abundance of water’s circulation remained in even the most purified distillations of the concept: “The waters of the earth” reported T. H. Huxley in his 1877 edition of Physiography, “move in a continued cycle, without beginning and without end. From rain to river, from river to sea, from sea to air, and back again from air to earth—such is the circuit in which every drop of water is compelled to circulate” (Huxley [1877] 1907, 76).

Before leaving Tuan’s study, a couple of points might be stressed. First, rather than treating the hydrologic cycle as a fact of nature, Tuan was attentive to its constructedness: “For in its finer expressions the concept does honour to the ingenuity of the human mind if not indeed to the wisdom of God” (Tuan 1968, 6). Furthermore, the geographical location of its construction—in northwestern Europe—was deemed significant: In proclaiming the wonders of God’s sublunary water works, “scholars of northwestern Europe were helped in their delusion by the well-watered—and even drenched— landscapes they saw constantly about them” (Yuan 1968, 144). Moreover, as water was translated from Christian to Darwinian scientific catechism, some aspect of this delusion was carried over, as Tuan seems to be saying when he writes, “In 18th century England the idea of a well-watered Earth was an unexamined article of faith to those who have fallen for the pervasiveness of the hydrologic cycle and to those who have allowed themselves to generalize from a very limited experience” (Tuan 1968, 144; italics added).

Second, although he acknowledged the constructedness of its natural-theological, or sacred variant, Tuan did not quite develop a critique of the hydrologic cycle itself. Throughout his study, titled The Hydrologic Cycle and the Wisdom of God, he used the term “hydrologic cycle” un-self-consciously, never considering that its coinage postdated by a considerable margin the written works that he studied. Had he considered this, it is possible that Tuan would have recognized that the hydrologic cycle itself is the product of particular historical circumstances, just as the sacred hydrologic cycle was the product of seventeenth- to nineteenth-century theological debates, and that it, too, internalizes a particular bias.

Horton (1931)

All the components of the water cycle concept had been proven mathematically and were ready for assembly as a complete system as early as the first decade of the nineteenth century. By the latter part of the century, scientists like Huxley, as quoted earlier, had done much of the necessary work, yielding “a continued cycle . . . [fr]om rain to river, from river to sea, from sea to air, and back again from air to earth” (Huxley [1877] 1907, 76). It remained only that the concept be given a name and rendered in the form of a visual representation. This was accomplished by an American hydrologist in a paper read at a meeting of the American Geophysical Union in 1931. Robert Horton’s “The Field, Scope, and Status of the Science of Hydrology” was written from his home in Voorheesville, New York, and published in Transactions of the American Geophysical Union the same year (Horton 1931). In addition to introducing English-speaking readers to the hydrologic cycle, Horton produced a diagram to illustrate it (Figure 2).

The purpose of Horton’s hydrologic cycle was to stake a disciplinary claim to water—all the water at, above, and beneath the Earth’s surface—on behalf of the emerging science of hydrology. Prior to Horton’s intervention, the basic concept that he described in terms of the hydrologic cycle was certainly understood by hydrologists and other scientists. However, in the United States (as elsewhere), the term hydrology usually applied to the study of “underground-water phenomena” well into the twentieth century (Horton 1931, 190). Furthermore, atmospheric hydrological phenomena were seen by many to fall within “the domain of meteorology,” particularly in the United States (Marvin 1923, 54; see also Marvin 1920, 566–67). If hydrology was to make room for itself as an ambitious earth science, it required an ambitious unifying concept. A few decades earlier, W. M. Davis had presented his famous “geographical cycle,” which had been instrumental in organizing and systematizing geography in the United States and had the effect of claiming the (study of) landforms for geography in Anglophone academe (W. M. Davis [1899] 1954; Chorley, Beckinsale, and Dunn 1973; Kennedy 2006, 87–97). Whether or not Horton sought to emulate Davis’s success, his hydrologic cycle effected a similar acquisition for hydrology, bringing the entire hydrosphere into its remit while distinguishing hydrology from the other geosciences.

In the United States, proposals to establish a separate Hydrology Section of the American Geophysical Union (AGU) had been rejected by the leadership of the Union on the basis that “active scientific interest in the U.S. did not justify a separate section of scientific hydrology within the AGU” (National Research Council 1991, 40). Finally, when the AGU was transformed from a committee of the National Research Council into an independent society in 1930, approval was given to establish a separate Section on Hydrology with R. E. Horton as vice-chairman. At the AGU’s 1931 meeting, Horton delivered his paper:

"Defining science as correlated knowledge, it is true that a statement of the field, scope, and status of hydrology at the present time may be little more than a birth-certificate. Nevertheless, there is scattered through scientific and engineering literature a mass of quantitative results adequate to make a most respectable body of science, wanting only to be coordinated. . . . In one sense the field of hydrology is the Earth and so is co-terminous with other geo-sciences. More specifically, the field of hydrology, treated as a pure science, is to trace out and account for the phenomena of the hydrologic cycle. . . . Again, hydrology may be regarded as charged with the duty of tracing and explaining the processes and phenomena of the hydrologic cycle, or the course of natural circulation of water in, on, and over the Earth’s surface. This definition has the advantage that it clearly outlines the field of hydrologic science. (Horton 1931, 190, 192)"

Figure 2. Horton’s illustration of the hydrologic cycle. Source: Horton (1931, 193). Copyright © 1931 American Geophysical Union. Reproduced by permission of the American Geophysical Union.

The naturalness of the hydrologic cycle is built right in to its constitution; to repeat Horton’s phrase, it is “the course of natural circulation of water in, on and over the Earth’s surface” (Horton 1931, 192, italics added). The natural pedigree of the hydrologic cycle was ensured, moreover, by establishing its mathematical credentials; Horton was certain to ground the hydrologic cycle on the solid, mathematical foundation of the water balance equation. “There is,” he asserted, “a simple basic fact involved in the hydrologic cycle: Rainfall = Evaporation + Runoff ” (Horton 1931, 190). By positioning the hydrologic cycle squarely in the natural realm, Horton effectively sealed the claim for hydrology as a “pure science.” By channelling all water through the hydrologic cycle, all water was claimed as the object of hydrological investigation.

To varying degrees, something like the concept of the hydrologic cycle was implicit in the work of people who considered themselves hydrologists in the United States and elsewhere before Horton’s intervention. Horton himself points out that texts and periodicals dealing with various aspects of hydrology had been published in other languages, especially German, Russian, and French, beginning in the late nineteenth century (Horton 1931, 190–91, 202). However, like the earlier American publications that could qualify as hydrology texts (e.g., Meyer 1917, 1928; Mead 1919) and a mid-nineteenth-century British Manual of Hydrology (Beardmore 1862), nothing quite like the hydrologic cycle was present in these.1 It was of the status of the science generally that Horton (1931) wrote, “The development of hydrology, owing to lack of centralization and lack of coordination, has been extremely unbalanced” (191).

After its crystallization in Horton’s paper, however— and ever since—“the hydrologic cycle” has been quoted, copied, and proclaimed as the core concept of hydrology in the Anglophone tradition.2 In the first American hydrology textbook published subsequent to Horton’s 1931 paper, its editor, O. E. Meinzer, declared, “The central concept in the science of hydrology is the so called hydrologic cycle—a convenient term to denote the circulation of the water from the sea, through the atmosphere, to the land; and thence, with numerous delays, back to the sea by overland and subterranean routes” (Meinzer 1942, 1–2). A diagram of the hydrologic cycle was featured on the frontispiece of Meinzer’s book. And so the hydrologic cycle has remained to the present, always figuring prominently in textual and diagrammatic form—and identified as the central concept, or framework of hydrology—in the introductory pages of almost every textbook, handbook, and general study published on hydrology and by hydrologists. Through habit of use, however, the hydrologic cycle is no longer “so-called,” but is now presented as a veritable natural fact.3

The Hydrologic Cycle and the State

The issuance of hydrology’s birth certificate occurred at a propitious moment for water in the United States, as the federal government was about to embark on what was perhaps the most ambitious program of fluvial manipulation ever undertaken. As we shall see, the hydrologic cycle, especially in its visual form, was readily adapted to the needs of state planning agencies in the 1930s to make water visible—or “legible” (Scott 1998)—for the purpose of accounting for, and controlling, it. Water was by no means the only force to be made known and disciplined by the state at this time; the Great Depression provided the circumstances in which centralized, scientific management was imposed on a wide range of processes (social and natural) in the United States and elsewhere. An effect, or corollary, of this imposition was to reinforce—if not to establish—fixed representations of these processes. Timothy Mitchell has shown how “the economy was formed as a new discursive object” in the 1930s “as the field of operation for new powers of [state] planning, regulation, statistical enumeration and representation” (Mitchell 1998, 82, 91). The scientific basis for “fixing the economy,” Mitchell argues, was provided by the nascent practice of econometrics, or “the attempt to create a mathematical representation of the entire economic process as a self-contained and dynamic mechanism” (Mitchell 1998, 85). A similarity with water might be suggested: Via Horton, hydrological science had established a mathematically structured representation of the water process as a self-contained and dynamic mechanism, one that, like the economy, was readily taken up by the state as a discursive object.

General principles for scientific development and management of the nation’s water resources had been worked out during the conservation movement in the early part of the century (Hays 1959). It was not until the mid-1930s, however, under Franklin D. Roosevelt’s New Deal programs, that these principles were put into effect and monumentalized in programs like the Tennessee Valley Authority and in physical structures such as the Hoover Dam. The political circumstances of the Depression allowed for what Donald Worster (1985) has described as “an immense ballooning of the state” (279) in terms of its capacity to account for, represent, and assume control of the nation’s natural resources, water in particular (Linton 2006a). The most comprehensive and ambitious thrust of federal resource strategy under the New Deal was to promote “a unified plan of water control” based on the philosophy of multipurpose water planning and integrated development of the nation’s river basins (National Resources Committee 1937, 7; Maass 1970, 100–101). A series of agencies established by the President to promote the coordination of national resource conservation and development—the National Resources Board (1934–1935), National Resources Committee (1935–1939), and National Resources Planning Board (1940–1943)—devoted considerable effort to this undertaking. “[T]heremust be,” declared the National Resources Board in 1934,

national control of all the running waters of the United States, from the desert trickle that may make an acre or two productive to the rushing flood waters of the Mississippi. . . . There is no stream, no rivulet, not even one of those tiny rills which cause “finger erosion” in the wheat fields of the Corn Belt, that is not a matter of some concern to all the people of the United States. (National Resources Board 1934, 255)

To even imagine their “national control,” it was necessary to find the means by which “all the running waters of the United States” could be made known and available to state planners. Following Horton’s 1931 paper, a diagram depicting the hydrologic cycle appeared in a 1934 report of the National Resources Board that highlighted the need to rationalize and centralize water planning (Figure 3). “The key to the beneficial control and use of the waters of the country is to be found in recognition of four unities,” the report declares; “Unity of Physical Factors . . . Unity of Man’s Interests . . . Unity of Responsibility . . . Unity of Action” (National Resources Board 1934, 260–63). Literally in the midst of these declarations of unity—unifying all these principles, as it were—appears this diagram of the hydrologic cycle, which is described as a means of conceptualizing “the extremely complex and diverse phenomena producing and affecting the water resources of the country” (National Resources Board 1934, 292).

In contrast to Horton’s diagram, this simplified version appears to be the first example of what has been labeled a “descriptive” hydrologic cycle diagram (Chow 1964, 1–3). As this style has become the most common way of depicting the hydrologic cycle, the diagram shown in Figure 3 could be considered the prototype of a foundational image in the visual discourse of modern water. As a means of helping make water legible for state administration and control, this version has helped structure an understanding of water for which large-scale engineering solutions may be seen (literally) as the norm (Figure 4).

The hydrologic cycle provided a means of visualizing and comprehending the nation’s water in a way that could be used as a model and as an argument for the need to collect comprehensive, integrated hydrometric data. To assert control over the nation’s water, the necessary first step was to correct the vast “Deficiencies in Basic Hydrologic Data” that were seen to pertain throughout the country (National Resources Committee 1937). To correct for these perceived deficiencies, the National Resources Committee proposed a program for nationwide coordination and standardization of hydrological data gathering. The hydrologic cycle was brought onto the scene at this time as a means of coordinating a vision of what was needed: “Water-conservation measures in the past” declared the Committee, “have been hampered by lack of basic data concerning the hydrologic cycle” (National Resources Committee 1937, v). Development of water resources depends on “exact knowledge of such factors as rainfall, snowfall, the flow of streams, the level at which water stands in the ground, the rate at which it evaporates or at which it transpires from trees and other vegetation, and the chemicals, suspended matter, or impurities which are found in it.” More succinctly, “What we need to know,” is identified precisely as “The Hydrologic Cycle” (National Resources Committee 1937, 1–2).

By virtue of its relative simplicity, its inclusion of stylized images of recognizable landscape features, and the ease with which it could be read and assimilated by people living in the temperate regions, this type of diagram attained immediate popularity within and beyond hydrological discourse, such that it could be described as “the hydrologic cycle . . . as conventionally drawn” in 1938 (Leighly 1938, 335) and “the usual form” by 1940 (Jenkins 1940, 309).4

Is the Hydrologic Cycle Sustainable?

A working definition of sustainable water use . . . is the use of water that supports the ability of human society to endure and flourish into the indefinite future without undermining the integrity of the hydrological cycle or the ecological systems that depend on it. (Gleick 2000, 131). The thesis conveyed by these pages is simple. Nature is the source of water; therefore our ability to support additional human lives on planet Earth depends upon the protection of nature and the continued operation of the water cycle. (Hunt 2004, 1)

In the first half of this article, I considered the hydrologic cycle as an abstraction, the modern form of which began to circulate in the 1930s. The history of this abstraction, however, has been lost to the general memory, a loss made secure by the hydrologic cycle’s constitution as “the course of natural circulation of water” (Horton 1931, 192). Today, after having internalized the hydrologic cycle, it is only natural that we should wish to sustain it. Who, after all, would wish to disintegrate or halt the operation of the natural circulation of water? By now, however, it should be clear that the question of sustaining the hydrologic cycle can be understood in a different way, namely: What does it mean to sustain such an abstraction? As I argue in the second half of the article, sustaining the modern hydrologic cycle might actually do more harm than good for the protection of aquatic ecosystems and the provision of water services for more people—goals that are often pursued in its very name.

Figure 3. Precipitation and the hydrologic cycle. Source: National Resources Board (1934, 262).

The Hydrologic Cycle and the “Humid Fallacy”

To state the obvious, the hydrologic cycle represents the nature of water as a cyclical process, in which regularity is maintained in the balance of the cycle’s various phases. The mathematical balance of the modern hydrologic cycle often inspires a sense of wonder reminiscent of its sacred precursor, as reflected in the prize-winning5 book, Water, by the Canadian author Marq deVilliers: “Water exists, then, in a closed system called the hydrosphere, and contemplating the hydrosphere and the hydrologic cycle is almost enough to make a sceptic believe in the omni-existent Gaia. The system is so intricate, so complex, so interdependent, so all-pervading, and so astonishingly stable that it seems purpose-built for regulating life” (de Villiers 1999, 29).

Figure 4. Round and round and round it goes. Note how the dam fits naturally into the hydrologic cycle. Source: National Research Council (1991, 18). Permission to reproduce this figure was granted from the Copyright Clearance Center (CCC).

One need not be a skeptic to question the hydrologic cycle’s astonishing stability, however; one need only live in a part of the world that does not share the astonishingly temperate hydrological conditions of northwestern Europe and northeastern North America, from where the sacred and the modern hydrologic cycles sprang forth. In contrast with northern temperate regions, mean annual precipitation varies from practically none—in parts of northern Africa, the northern polar region, central Asia, central Australia, and parts of South America—to more than three meters in the equatorial zone and as much as ten meters in some tropical mountainous and monsoon regions. Also, the relative evenness of precipitation enjoyed from month to month and year to year in the temperate regions is belied by the experience of hydrological variability among a very large—and growing—proportion of the world’s population. Delhi, for example, receives about the same amount of annual precipitation as London, but this typically arrives in torrents in July and August (about 180 mm each) and is negligible in November (about 10 mm). Furthermore, in western Europe and eastern North America, annual rainfall varies by less than 15 percent per year, whereas in semiarid and arid regions, it tends to fluctuate by 40 percent or more (Bergman and Renwick 2002, 72). As Mike Davis has said of the Mediterranean climates of places like Southern California, west and south Australia, parts of Chile, South Africa’s Cape Province, and the Mediterranean itself, “nothing is less likely to occur than average rainfall” (M. Davis 1995, 226).

By representing water as a constant, cyclical flow, the hydrologic cycle establishes a norm that is at odds with the hydrological reality of much of the world, misrepresenting the hydrological experience of vast numbers of people. Furthermore, the adoption of such a norm has the effect of conditioning expectations and coloring judgments. The hydrologic cycle helps uphold a long-standing Western prejudice against aridity, by which places (and often the people inhabiting them) lacking “sufficient” rainfall, or subject to “violent” swings in seasonal and annual precipitation must be regarded as deficient, abnormal, and in need of hydrological correction. Tuan cited the hydrologic cycle as “a factor that led to the slighting of the dry lands” (Tuan 1968, 144).6 Although he was referring to what I have distinguished in terms of the sacred hydrologic cycle, the modern variant also helps sustain the prejudice.

It can be argued that the temperate bias of the modern hydrologic cycle helped sustain—until very recently—what might be described as hydrological Orientalism: the (mis)apprehension and portrayal of deserts, arid lands, and tropical regions as respectively barren, poor, uncivilized, lawless, and violent places (and peoples) that require the intervention of hydrological engineering to be made civilized. “Imperialism after all,” wrote Edward Said, “is an act of geographical violence through which virtually every space in the world is explored, charted, and finally brought under control” (Said [1988] 2000, 297). Of few spaces does this ring truer than the waterways of colonized peoples and places. To borrow a phrase used by Donald Worster, “imperial water” had been brought to every continent by the mid-twentieth century (Worster 2006; see also Gregory 2001, 96–97).

Imperial water did not stop flowing with the end of imperialism proper, however. In the second half of the twentieth century, along with the hydrological engineering of its own internal empire (see later), the United States helped carry the imperial conquest of water forward in the name of international development. Immediately after World War II, Michael Straus, President Truman’s Commissioner of Reclamation, described the control of water “as a prerequisite of all development and elevation of living standards” and vaunted that “the American concept of comprehensive river basin development . . . has seized the world imagination. Yellow, black, and white men of various religions in all manner of garb are seeking to emulate the American pattern of development” (Worster 2006, 11).What first seized theworld imagination—including that of local elites in the development process—was the idea that even-flowing rivers and lakes (or artificial reservoirs) characterize a civilized world, and that no country can embark on a respectable program of modern development without them. Jawaharlal Nehru’s famous description of dams as “temples of modernity” reflected a widespread urge to reassign the sacredness of specific rivers and their unique hydraulic regimes to the worship of even streamflow.

The modern hydrologic cycle can thus be seen as helping uphold a discourse that makes the association of dams and development seem only natural (Figure 4). Its invention—in the eastern part of the United States in the early 1930s—corresponds to the Americans’ own home-grown brand of contempt for aridity. As Worster (2006) has so well elaborated, “from the mid-1930s to themid-1960s, the federal government managed to turn every major river in the arid [American] West into a series of man-made lakes, building thousands of dams and reservoirs” (10; see also Worster 1985). Several commentators have recognized the urge to procure temperate hydrological conditions in the arid American West as a cognitive error (and identity problem) of gargantuan proportions. Describing what he calls the “humid fallacy, ”Mike Davis notes how “deeply engrained prejudices about climate and landscape that had been shaped by the environmental continuum of North-western Europe and the Eastern United States . . . still condition environmental expectations in Southern California” (M. Davis 1995, 226).The “humid fallacy” as Davis describes it has inspired hydraulic manipulation in the southwestern part of the continent on a scale sufficient to lubricate the dreams of Southern Californians and provide (at least temporarily) some measure of security against their “almost irrational fear of aridity” (M. Davis 1995, 224; see also M. Davis 2002, 87). Wallace Stegner has poked an equal measure of fun and scorn at the drenched imaginations of those who will not or cannot see that “living dry” is the only appropriate human response to the American West (Stegner 1998, 213–29). “Aridity,” he cautions, “makes all the difference.” Failing to recognize this difference and the hydrosocial imperatives that aridity implies, however, the typical response has been “engineering it out of existence” (Stegner 1998, xii, 229).

The Hydrologic Cycle and “Blue Water” Bias

In addition to its cyclicity, another obvious feature of the hydrologic cycle is what we might call its “blue-water bias.” The hydrologic cycle normalizes an experience of water that presumes the prominence of streamflow, or flowing, liquid surface water. Because descriptions and diagrams of the hydrologic cycle always include the flow of water over and through the land en route to the sea as an essential phase of the cycle, they help contribute to the idea that water resources should be envisioned predominantly as lakes and rivers—or blue water (Falkenmark 2005). As with the humid fallacy more generally, the “blue water” bias of the hydrologic cycle internalizes a particular human experience with water and generalizes this experience to make it the norm (Falkenmark 2005, 9–10). Here, I mean “make it the norm” in the active sense of applying technologies that enable people to exploit—or create—stocks of liquid water wherever and whenever water resources are required. So long as blue water is integral to its design, sustaining the hydrologic cycle means ensuring the adequacy of these stocks for human purposes. The irony—as suggested in the quotes by Gleick and Hunt cited earlier—is that by engineering the accumulation of these stocks on a scale that has produced obvious and harmful consequences for aquatic ecosystems, the hydrologic cycle itself is thought to be at risk.

This concept of blue water derives from the work of Swedish hydrologist Malin Falkenmark. Falkenmark has long advocated water resource management techniques that are better suited to the actual conditions— hydrological as well as social—of people living in arid and semiarid regions than the techniques that have dominated international water development (e.g., Falkenmark 1986, 1989, 1996, 2005). Among her concerns has been the common predisposition to see the storage and distribution of liquid water as the natural means of developing water resources.7 Such a view has regard only for blue water, which in many places only constitutes a small portion of the overall water resource. Blue water, for instance, does not include soil moisture destined for transpiration by plants, a distinct resource Falkenmark calls “green water,” which is “the main water resource involved in rain fed crop production and in biomass production in natural terrestrial ecosystems. Therefore,” she stresses “one urgent shift in thinking is to move from seeing only blue water as the economic resource to also seeing green water as a resource” (Falkenmark 2005, 9–10).

Falkenmark’s green water corresponds to a portion of the hydrologic cycle that traditionally has been considered by hydrologists in terms of “losses” (Klemes 1988, 20). The notion that only liquid water runoff and streamflow may be considered useful to people is embedded in the very constitution of the hydrologic cycle, wherein Horton took pains to “define runoff as equal to rainfall minus water losses. Water-losses are of three kinds, all evaporative in their nature: (a) Interception; (b) transpiration; (c) direct evaporation from soils and water-surfaces” (Horton 1931, 190). By subtracting transpiration from runoff and by describing it as a loss, this formulation effectively removes green water from the category of useful water resources. Other potential and actual sources of exploitable water—such as intercepted rain or fog—are similarly left out of the picture. Although such an appraisal might have seemed natural in the historical and geographical context of industrial America in the 1930s, the application of “losses” to these portions of the hydrologic cycle seems amiss in other circumstances: Evaporation is not a loss to the hydrosphere, or to nonhuman nature; it may be considered a loss only by those for whom the available water flowing in rivers, stored in lakes, or held in aquifers is what really counts—in other words, those for whom only flowing, liquid water is seen as a resource.

The modern hydrologic cycle emerged within a particular set of historical and geographical circumstances wherein the financial and technological capacities of the state were being harnessed for the purpose of exploiting available supplies and flows (as in hydroelectrical generation) of surface water. Those historical and geographical circumstances no longer pertain in the United States and elsewhere. With some exceptions (most notably China and India), the state is no longer in the business of building dams and ancillary waterworks on the scale of the late twentieth century. Even were it to have the political capacity to do so, the intensity of water development in the past has effectively used up readily available supplies; moreover, much of what is left is now considered necessary to maintain aquatic ecosystem functions (Gleick 2000).

These new historical circumstances have produced a paradigmatic change in the way resource managers think about satisfying demands for water (Gleick 1998, 2000). Under the old paradigm, water management was conceived mainly in terms of harnessing and transferring liquid water supplies for various and growing human needs, a program that was easily conceptualized and visualized through the hydrologic cycle. The overall goal of water management, as described by a leading authority, was “that man can progressively increase his ability to modify the hydrologic cycle to his advantage” (Thomas 1956, 556). The notion of modifying the hydrologic cycle fits awkwardly, if at all, into the new paradigm, hence the calls for maintaining its “integrity” and its “operation.” Peter Gleick defines the “changing water paradigm” as

a shift away from sole, or even primary reliance on finding new sources of supply to address perceived new demands, a growing emphasis on incorporating ecological values into water policy, a re-emphasis on meeting basic human needs for water services, and a conscious breaking of the ties between economic growth and water use. . . . At the same time, new methods are being developed to meet the demands of growing populations without requiring major new construction or new large-scale water transfers from one region to another. (Gleick 2000, 127)

Given the comfortable—even symbiotic— relationship between the hydrologic cycle and the old, supply-oriented paradigm of water resource management, one wonders whether this relationship, and the hydrologic cycle itself, will be able to withstand the challenges that are certain to redefine the nature of water resources over the next century.

Is the Hydrologic Cycle Losing Steam?

Perhaps a greater challenge is suggested by recent indications from the hydrological sciences that the modern hydrologic cycle might be losing its grip on the world’s water. As already noted, the hydrologic cycle continues to serve the purpose of framing the field and scope of hydrology, as it has done since Horton’s time. Nonetheless, hydrologists seem wary of the concept. As early as 1968, Tuan observed of his contemporaries in North America and Europe, “hydrologists are feeling less and less happy with the [hydrologic cycle] concept. As commonly stated and illustrated it appears so loose and generalized as to be almost meaningless. Certainly it is of little applied use” (Tuan 1968, 4). Today, possibly with greater frequency in British textbooks, the perfunctory introduction and diagram of the hydrologic cycle as the “central concept of hydrology” is hedged with caveats indicating the complexity of the actual behavior of water. “Inevitably,” declares one such text, “the simplifications and generalizations involved in the broad concept of the hydrologic cycle may be misleading unless treated with caution. Thus, the implication of a smooth, uninterrupted, sequential movement of water is belied by the complexity of natural events” (Ward and Robinson 2000, 4).

Further evidence of dissatisfaction with the modern, conventional hydrologic cycle comes from hydrologists working in places where it might always have been regarded as a foreign concept. An alternative outlook described by Ian Calder as The Blue Revolution provides an example (Calder 1999, 2005). Despite its title, the hydrological argument of the Blue Revolution bears similarities to Malin Falkenmark’s efforts to counter the presupposition by which water resources are so easily associated with the management of streamflow. Calder’s experience as former Chief Water Resources Officer in Malawi and as Hydrology Adviser to the British Overseas Development Administration has provided ideas for what he describes as “a revolution in the way land and water are managed” (Calder 2005, 1) that sheds at least some8 of the imperialisticmanagement tendencies alluded to earlier, thus gaining the attention of political ecologists (Forsyth 2003, 36–37, 90, 138).

At the center of this revolution is “a new understanding of how land use influences hydrological processes and water resources” (Calder 2005, 2). Understanding the dynamics of this influence has always been an important aspect of hydrological investigation, but in this case, the processes and resources in question are particular to local circumstances in the global south. From the perspective of researchers working in southeastern Africa, for example, the evaporative functions of different types of vegetation cover and the resource identified earlier as green water are more important than in temperate regions. In circumstances where evaporative demand typically exceeds the supply of transpirable water (i.e., green water), factors such as the height, aerodynamic resistance, and transpiration characteristics as well as the root depth of the vegetative cover, determine movement of water through the landscape. The Blue Revolution emphasizes investigation of the relationship between characteristics of vegetative cover and rates of interception, transpiration, and surface evaporation. Calder points out that hydrologists usually estimate evaporation using methods that focus on the atmospheric demand for evaporated water— methods that have been developed in temperate climates:

Evaporation equations, based on the concept of the energy balance and the aerodynamic transport equation . . . are [therefore] central to most of the modern hydrological methods of estimating evaporation from different surfaces. . . . This may be entirely appropriate in the temperate climates of the world where these evaporation equations were developed, but in many parts of the world, particularly in the very dry regions, the actual evaporation is perhaps only a small fraction of the demand and it may be more reasonable to estimate evaporation from considerations of limits on supply. (Calder 2005, 63–64)

Calder is perhaps best known for challenging hydrological “myths and mother statements” that continue to circulate partly as a result of the unexamined transfer of hydrological experience and methods in the global north to the south. He has been especially critical of what he calls “forest hydrology myths” (Calder 1998, 1999, 2005) that gained currency in the United States in the early twentieth century, and that link forest cover with benefits such as increased runoff, more evenly regulated streamflow, increased dry season flows, reduced erosion, and reduced flooding (Calder 2005, 29–62; Dodds 1969). Calder draws from numerous studies to show that in many cases, forests of the global south tend not to function in accordance with these observations: Instead of increasing and regulating runoff, they can actually promote evapotranspiration at rates much higher than for short crops, and have the overall effect of reducing the quantity of water available for runoff or groundwater recharge (Calder 2005, 20–29).

The implications of these investigations for land-use management are important, but what is of most interest here is that the Blue Revolution has no use for the hydrologic cycle, per se. As a framework for conceptualizing and visualizing the movement of water, the standard hydrologic cycle is hardly appropriate in regions where the pathways of interception, transpiration, and evaporation from vegetation and the soil are more significant than runoff and streamflow. The standard hydrologic cycle is of less relevance in circumstances where people are generally more concerned with promoting productive and sustainable land use than capturing and manipulating streamflow. Calder’s text includes no discussion or diagram of the standard hydrologic cycle; it does, however, feature a diagram (and detailed description) of “principal evaporation pathways” (Figure 5). This schema could be considered a special case of the hydrologic cycle that is relevant to a given place by emphasizing evaporation at the expense of runoff and streamflow. Even so, it suggests a shift in hydrological discourse—one that attends less to the universal nature of water than to local hydrological and social circumstances.

A latent threat to the hegemony of the modern hydrologic cycle may be found in the work of hydrologists and other earth scientists who address themselves to the historical condition that is best represented by the term Anthropocene to denote “the present, in many ways human-dominated, geological epoch” (Crutzen 2002, 23). Recognition of the increasingly social nature of water’s disposition on the face of the Earth is giving rise to models of far greater subtlety and complexity than the standard hydrologic cycle can withstand. The very idea of the Anthropocene is injurious to the hydrologic cycle, and not only because it renders any notion of “the natural circulation of water” problematic. In its association with anthropogenic climate change, for example, the Anthropocene upsets traditional notions of nature’s balance and stability. Growing preoccupation with climatic instability and the possibility of dramatic change in the natural conditions that sustain human societies is starkly antithetical to the presumption of order, balance, harmony, and equilibrium in natural processes—a presumption on which the hydrologic cycle rests.

In this regard, it might be pointed out that the standard hydrologic cycle reflects a scientific paradigm that is increasingly thought to be inadequate. Since the early 1980s, new models and metaphors have come from mathematics, physics, biology, and ecology that emphasize nonlinearity, historical contingency, and disturbance in natural processes at all scales (e.g., Botkin 1990; Worster 1990; Prigogine 1997). These developments have had considerable impact within and beyond the “natural” sciences. Political ecologists, for example, have focused critical attention on the way “equilibrium thinking” pervades discourses of development, environmental intervention, and management of natural resources (Scoones 1999). Given its implications for theorizing the relationship between humans and nature, the potential for “integrating the ‘new ecology’s’ interpretation of nature into human geography” has been recognized within the discipline as an important avenue of investigation for over a decade (Zimmerer 1994, 115). Among physical geographers also, there is felt the need to reflect critically on the ahistorical-process approach that has served as a paradigm for geomorphology since Strahler’s intervention in the early 1950s (Strahler 1952). “What is needed is a broadening of the dynamic basis [of geomorphology] by expanding the notion of process to encompass mechanistic, historical, and ‘nonlinear dynamical’ geomorphological explanations” (Rhoads 2006, 17; see also Roy and Lane 2003). Scholars in a wide variety of fields, it seems, are interested in new ideas and models that would better reflect an understanding of natural processes as time dependent and contingent.

In such circumstances it is somewhat surprising that the hydrologic cycle has not already been singled out for critique. Even before Strahler, Robert Horton formulated a quantitative, dynamical basis for geomorphological investigation that was instrumental in eventually overturning the long-standing Davisian model of landscape development (Kennedy 2006, 102–06) Thus Horton’s (1945) paper detailing a “Hydrophysical Approach to Quantitative Morphology” has been identified as “the crucial springboard” for the “Reductionist Revolution” in geomorphological thought, which is usually associated with Strahler (Kennedy 2006, 98; see also Rhoads 2006; note 3 in this article). It is no mere coincidence that the inventor of the modern hydrologic cycle and the instigator of the reductionist process paradigm are one and the same person. The hydrologic cycle offers a prototypical model of a quantitative dynamic process that seems increasingly at odds with contemporary thought in all the sciences. Its longevity is all the more remarkable given that some hydrologists have drawn attention to the way water exhibits extremely complex, nonlinear responses “resulting from the effects of spatial variability in rainfall, vegetation canopy, soil structure, and topography” (Beven 1987, 400; see also Beven 2000).

Figure 5. Principal evaporation pathways. Source: Calder (1999, 7). Permission to reproduce this figure was granted from the publisher, Earthscan.

The intellectual conditions that call for a reconsideration of the hydrologic cycle might just as soon arise out of popular discourse as from scientific scrutiny. It is now common knowledge that hydrological phenomena are bound to exhibit rather wild tendencies in association with climate change. Considering the content of the daily news, these phenomena are already very much in the public eye. Anomalies in such things as annual and seasonal precipitation, sea levels, lake levels, river flows, rates of evaporation, rates of glacier and permafrost melting, and frequency and intensity of floods and droughts are monitored by the media and the public with a high degree of apprehension. As change and flux condition the hydrological awareness and expectations of more andmore people, onewonders what future there is for the modern hydrologic cycle in the public imagination, with its reputation for being “so astonishingly stable that it seems purpose-built for regulating life” (de Villiers 1999, 29).

Where alternative concepts do arise in scientific discourse, they appear to be formulated for the purpose of conceptualizing the (social) nature of water in the twenty-first century. Although hydrologists and others have long considered the question of human impact on the hydrologic cycle (e.g., Thomas 1956), the incorporation of human society in our understanding of the natural disposition of water demands new forms of representation. The hydrologic cycle, we might say, can no longer withstand the human assault, such that its very character is being altered: “Evidence now shows that humans are rapidly intervening in the basic character of the water cycle” states the Global Water System Project, a major international research effort that facilitates integrated study of the “biogeophysical and social dimensions of the water system” (Vӧrӧsmarty et al. 2004, 509, 514). “The freshwater cycle,” concludes the framing statement of the Project, “is under rapid transformation” (513).

This statement may be understood in two ways: Clearly, as the authors point out, anthropogenic interventions—like climate change, basin-scale water balance changes, river flow regulation, sediment fluxes, chemical pollution, microbial pollution, and changes in biodiversity—are having the effect of “transforming the contemporary global water system” (Vӧrӧsmarty et al. 2004, 514).Although not entirely dispensing with the traditional language of the “water cycle,” it is also clear that they—the authors of the article—have radically transformed it (Figure 6). The “water cycle” is now understood as the integration of physical, biological, biogeochemical, and human components of a more general “global water system.” Now it is the water system that represents the nature of water, a nature that is highly complex, and arguably—to apply a term of the sort used more and more by critical geographers— “indeed social through and through” (Braun and Castree 1998, xiii).

Conclusion: What Becomes of Water

The growing awareness of and attention to the social nature of water poses a serious threat to the integrity of any concept that purports to represent water’s essential nature. As water breaks free of the constraints imposed by the modern divide between nature and society (Latour 1993), the adulteration of the hydrologic cycle by humans becomes an obvious matter of concern, as suggested in the earlier quotes from Gleick and Hunt. By now, however, it should be equally obvious that striving to maintain the integrity of such an abstraction as the hydrologic cycle is futile, except in the abstract, discursive sense in which it is sustained. A more constructive option is in treating the integration of water and people as a perfectly natural process rather than a form of pollution. Far from being an unthinkable disaster, the disintegration of the hydrologic cycle might portend the arrival of a new and promising era for water and for the people who cannot help but get mixed up with it.

Figure 6. The global water system. Source: Vӧrӧsmarty et al. (2004, 509). Copyright © 2004 American Geophysical Union. Reproduced by permission of the American Geophysical Union.

Geographers are in the forefront of research to articulate the “socioecological nature of water.”9 Some have suggested “hybrid freshwater ecosystems” as a point of departure for the production of healthy waterways where “it might not be possible, andmight even be detrimental, to delineate between the natural and the artificial” (Crifasi 2005, 626; see also Swyngedouw 1999; Urban and Rhoads 2003). It is in the study of urban water systems, however, where the distinction between the social and the natural is least tenable, and where geographers have most fruitfully developed concepts of hydrosocialmetabolism. For Erik Swyngedouw, the “hybridized waters” of cities offer a politically useful means of conceptualizing how “water . . . embodies, simultaneously and inseparably, bio-chemical and physical properties, cultural and symbolic meanings, and socioeconomic characteristics” (Swyngedouw 1996, 80, 76; see also Kaika 2005). Water’s collaboration in “the making of metropolitan nature” is further politicized in the writings of Matthew Gandy, offering a conceptual means to “to ‘rematerialize’ the city” in ways that promote environmental justice and uphold “the continuing political salience of the public realm” (Gandy 2003, 1022; see also Gandy 2005, 40–41). Increasingly, it is the “hydrosocial cycle” that—for geographers— describes the process by which water is enlivened by human affairs, and human affairs are enlivened by water (Bakker 2002, 2003; Swyngedouw 2004, 2005; see also Swyngedouw, Kaika, and Castro 2002). The task, already begun, is to put the “hydrosocial cycle” to work in helping promote social justice and environmental sustainability not just in cities, but wherever intervention in the hydrologic cycle has produced inequitable or uneven access to water and water services (e.g., Swyngedouw 2004; Budds forthcoming; note 9 in this article).

The adoption of these concepts and terms does not reflect a physical change in water as much as a change in the way water is seen. Rather than distinguishing something essential or natural—as in “the natural circulation of water on earth”—we tend to see a good deal more of ourselves in water than has been the case in recent (modern) history. Formerly, humans intervened in the natural water process, with the hydrologic cycle providing a means of visualizing and situating these interventions. Shifting from the hydrologic cycle to the hydrosocial cycle, from aquatic ecosystems to hybrid ecosystems, means seeing ourselves in the products of our collaboration with water instead of seeing water as something apart from ourselves. Itmeans that instead of trying to maintain the integrity of the hydrologic cycle we devote our efforts to maintaining a healthy working relationship with water, one that is conducive to the well-being of people, fish, benthic invertebrates, and the many others with a stake in this relationship.


Research for this article was supported by a doctoral fellowship from the Social Sciences and Humanities Research Council of Canada, which I am grateful to acknowledge. My sincere thanks go to Simon Dalby, Bill Nuttle, and Iain Wallace for their suggestions and support, particularly in the early phases of research. I also wish to acknowledge Karl Zimmerer and three anonymous reviewers, whose comments and suggestions have greatly improved this article.


1. Although Horton does not acknowledge it, Russian hydrologists had been working with a similar concept, “the rotation of water in nature,” since the late nineteenth century. The Russian term krugovorot vody v prirode (literally “rotation of water in nature”) may be defined as “the continual process of circulation of water on the globe, taking place under the influence of solar radiation and the force of gravity” (Robert North, personal e-mail correspondence, 18 May 2007). As pointed out by the Russian/Soviet hydrologist M. L’vovich, it was on the basis of this “great process” that Russian hydrologists worked out calculations for regional and global water balances beginning in the late nineteenth century (L’vovich 1972, 402). Although it bears obvious similarities to Horton’s hydrologic cycle, krugovorot vody v prirode does not appear to have provided a basis for the simple visual form by which the hydrologic cycle is typically represented (Linton 2006b).

2. The term “hydrological” cycle has been favored in the United Kingdom. Elsewhere, the hydrologic cycle had been translated, literally and diagrammatically, into many languages and found its way into hydrology textbooks around the world by the 1970s.Aswith the textbooks written in English, the hydrologic cycle appears to have been used for the same purpose of coordinating the discipline and framing its field and scope in the hydrology textbooks of other languages (see UNESCO 1974a, 1974b).

3. Robert Horton has been identified as the “father of American hydrology” (Hall 1987; National Research Council 1991, 41; Reuss 2001, 275), the foremost “leader” of the science (Leopold 1987, 27), and “the dean of American hydrologists” (Nace 1978, 23), but not for the reasons suggested in this article. Rather, it is his development of a quantitative approach to the development of streams and drainage basin topography that is always cited as his major contribution to hydrology, particularly his 1945 paper outlining a “hydrophysical approach to quantitative morphology” (Horton 1945).

4. The standardization of this depiction of the hydrologic cycle offended some meteorologists, who proposed, literally, redrawing it to account for atmospheric phenomena that they felt the hydrologists had left out of the picture (see Thornwaite 1937–1938; Leighly 1938; Jenkins 1940).

5. Winner of the (Canadian) Governor General’s Award for Non-Fiction in 1999.

6. It is reasonable to speculate that the roots of this prejudice may be located in biblical renderings of “wilderness” and “deserts,” inhospitable places bereft of water as well as the spirit of God (e.g., Jeremiah 17, 5–8).

7. The appropriate means of addressing the water needs of subsistence farmers in tropical, arid regions, Falkenmark has long argued, is to apply “a modified approach” that consists of exploiting the prerunoff portion of the hydrologic cycle instead of concentrating on conserving the streamflow portion (i.e., building dams), which has been the favored (most capital-intensive) Western approach. Her “modified approach” calls for small-scale projects directed toward what she calls “the short plant-producing branch” of the hydrologic cycle (Falkenmark 1986).

8. My comments are limited to the hydrological aspects of Calder’s book. The Blue Revolution advocates a suite of public policy prescriptions, many of which in my view do not necessarily flow from Calder’s hydrological investigations.

9. This was the title of a series of six sessions at the 2007 meeting of the American Association of Geographers (Association of American Geographers 2007, 180, 203, 226, 247, 454, 475). At the time of writing, the author is coorganizing (with Jessica Budds of the Open University) a panel and series of paper sessions on the theme of “the hydrosocial cycle” for the 2008 meeting of the AAG.


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