After describing the hydrological cycle and defining hydrology in the introduction, the early historical development of hydrology is briefly presented in the second section. Then the incorporation of hydrology within the IUGG and the subsequent development of the association are described chronologically. This description is organized into five sections corresponding to five different periods, focused on the scientific and organizational development of the association during each period. Finally, in the conclusions, the present state of the association is discussed together with an outlook for the future.
Determining what happens to
the rain when it hits the ground eventually leads to the concept of
When considering the central role of the hydrological cycle in the
definition, hydrology is primarily thought of as a branch of
The many diverse forms and occurrences of water on the Earth, and the many
different ways of utilizing water resources, gave rise to the concept of
The development of hydrology in the 19th century was dominated by the
emerging needs for
Towards the end of the last century, the growing
Philosophical descriptions of the hydrological cycle were developed in ancient Asian and Middle Eastern civilizations, where large irrigation and flood protection works were carried out. The concept of hydrology was described in both the old Greek (e.g. Aristotle) and Roman (e.g. Marcus Vitruvius) cultures, where impressive water engineering projects were developed, such as aqueducts and bridges.
It was, however, not before the beginning of the 1500s that a scientific approach to hydrology started to take off, albeit with a very slow starting speed. Leonardo da Vinci undertook physical experiments, e.g. measuring stream velocity, to support his advanced thoughts about hydrology (Pfister et al., 2009). In 1575, Bernard Palissy, based on observations in nature, claimed that springs originated from rain, and 100 years later, in 1674, Pierre Perrault measured the rainfall, runoff and drainage area of the Seine River and concluded that rainfall was enough to support springs and rivers. The pathways, however, were not correctly described. In 1686, Edme Mariotte supported the findings of Perrault by contributing infiltration experiments, relating them to precipitation regimes and developing better streamflow measurements. Around 1700, Edmond Halley published the results of evaporation measurements, thereby contributing significantly to closing the hydrological cycle. Nevertheless, it was not before 1802 that John Dalton became the first to give a complete and correct description of the cycle based on reliable observations (Dooge, 1974; Rodda, 2006). Thus, it took 300 years to lay the foundations for modern hydrology.
Leonardo da Vinci conducting experiments on the
velocity-distribution in streams. Source:
In 1738, Daniel Bernoulli published the equation for frictionless pipe flow. The 18th century brought further progress. Laminar pipe flow and turbulent river flow were described by, respectively, Gotthilf Hagen and Jean Poiseuille in 1840 and Antoine Chézy in 1776. During the 19th century, engineering became an important driver for further progress in hydrology. The fundamental equation for groundwater flow was developed by Henry Darcy in 1856. Flow from urban catchments was addressed by introducing the time of concentration by Thomas Mulvany in 1850, leading to the rational method for peak flow design, and in 1883, Wenzel Rippl introduced the mass curve for reservoir design.
The first half of the 20th century brought additional basic development. A description of soil infiltration and saturation was provided by William Green and Gustav Ampt in 1911, while Weston Fuller introduced statistical frequency analysis in hydrology in 1914. Later fundamentals comprised the equation for unsaturated flow by Lorenzo Richards in 1931 and introduction of the unit hydrograph by Leroy Sherman in 1932. In 1935 Charles Theis presented the equation for the drawdown of the piezometric surface caused by pumping from a well, and finally, to conclude the 50 years, in 1948 Howard Penman developed an equation for estimating potential evaporation based on measured meteorological variables.
In the following, the main emphasis will be on the institutional development during the last centennial to support hydrology. For a more science-oriented description of the development, the reader is referred to Sivapalan and Blöschl (2017).
At the general assembly of the IUGG in Rome in 1922, a delegate proposed a
motion to form an additional section within the union to deal with the
scientific problems in hydrology, such as “river-gauging, lake phenomena
including seiches, run-off and evaporation, transport of material in
suspension and in solution, glacier movement, etc.” A committee was set up
to give its opinion on the desirability of such a new activity. The committee
gave favourable advice and proposed that the new organism should be named
First IAHS President Edward Wade (left) taking flow measurements in the Nile River at Aswān in the early 1920s.
One of the reasons presented in the proposal was that the new organization would allow incorporation of the International Glacier Commission (CIG) that was founded in 1894, but had almost ceased to exist because of the First World War. At the 1924 General Assembly of the IUGG in Madrid, the Hydrology Branch created a “Commission for Glaciers” with the mission to assemble and publish data relating to glaciers. The inclusion of CIG in the Commission for Glaciers was approved at the Prague Assembly in 1927. Since snow issues became of greater interest, a “Commission on Snow” was subsequently created in the early 1930s. At the Edinburgh Assembly in 1936, it was decided to amalgamate the two glaciological commissions into a new “Commission on Glaciers and Snow”.
During the Madrid Assembly, a “Commission on Statistics” was constituted
with the task of trying to bring some uniformity into the publication of
hydrological data, and into the signs and symbols used. In addition, an
effort was made to bring together data on the state of hydrology in different
countries and to make an inventory of the water resources of these countries.
The first publications of the branch comprised mostly national reports from
this commission that served as background for two fundamental reports on,
respectively, surface waters and subterranean waters. The scientists
interested in this type of work were mostly hydraulic engineers, including
teachers of hydraulics, who supplemented their teaching with the principles
of hydrology. The report from the Madrid Assembly (IAHS, 1924) became the
first in the
Already in 1902, the first experimental basin study was initiated in the Emmental region of Switzerland (Whitehead and Robinson, 1993). In the 1930s, several additional studies were established assuming that in small experimental basins, it is easier to establish a water balance, and hydrological processes can be monitored and studied in detail. This methodology is generally accepted by the hydrological community as key to examining and observing small-scale hydrological phenomena.
The association began to cover an increasing number of hydrological
disciplines, and new commissions on potamology, limnology, instruments and
measurements, and subterranean waters were established. At the time of the
Washington Assembly in 1939, the association had produced 27 publications in
the series of Red Books. Because of the world war no IASH reports were published over the period 1939–1947. In 1935 the
Before World War II (1939–1945), hydrology, as it is understood today, was unknown to the public. Hydrology was not taught at universities as a separate subject. Fundamental aspects of it were included in such disciplines as physical geography and hydraulic engineering. However, during the period 1948–1970, hydrology became a generally recognized science of great significance for economic development. This had, of course, an enormous impact on the activities of IASH and its position in international scientific circles.
Post-war economic growth entailed a greater utilization of the natural resources of the Earth, water being one of the most important. Control and management of this resource became necessary in order to ensure adequate water supply for all sectors, together with flood forecasting and prediction. This could only be achieved by hydraulic works and structures, such as storage dams and reservoirs, diversion canals, embankments and groundwater recovery. The hydraulic design of these works required hydrological data extending over a sufficient number of years and sound knowledge of hydrological processes. This is especially true for the prediction of extreme events, such as major floods and serious droughts and their frequency of occurrence. Soon it was found that, in many cases, this sort of information was missing, and not only in developing countries. It was realized that the scarcity of hydrological information formed an obstacle to economic development, and that the water resources were limited even in humid zones. Thus hydrology, often mistakenly confused with water control, became an important discipline in the view of both decision makers and the public. This development lies behind the expansion of IASH in the period 1948–1970.
The meetings held during the General Assemblies of the IUGG in Oslo in 1948, in
Brussels in 1951, and in Rome in 1954, were attended by an increasing number of
participants of various backgrounds, such as hydraulic engineering, physical
geography, geology, hydrometeorology and water management. A need was felt to
organize more frequent meetings than would be possible within the framework
of the union assemblies. The first meeting of this type was the Darcy
Symposium in Dijon in 1956 on the occasion of the centenary of Darcy's law,
where not only groundwater but also evaporation and floods were discussed.
The frequency of these meetings, organized independently from the Union,
increased, and in the 1960s, hardly a year passed by without one or even two
symposia being convened under the primary responsibility of the association.
All proceedings were published in the
The
Publication of the quarterly
While the International Meteorological Organization, founded back in 1873,
had undertaken some hydrological activities, it was not until it was
transformed into a full intergovernmental organization as
In 1965, a major programme was launched by UNESCO as the
The same economic factors that promoted the expansion of IASH during the 1960s also led to a spectacular increase in the activities of other technical organizations in the field of water: hydraulic research, irrigation and drainage, large dams, water supply, water pollution, and so on. All of these associations were established after 1950. They included in their programmes many topics that were closely related to the activities of IASH without creating serious competition or duplication at that time. A body for mutual consultation and coordination of the scientific and technical organizations was established later.
In 1964, the International Council of Scientific Unions (ICSU), which
included the IUGG, created a
In 1967, it was decided that IUGG general assemblies should be convened every 4 years. This decision was of little consequence for IASH as most of its activities took place outside the union assemblies. More serious was the increase in workload of the IASH Secretary General (13 symposia and 25 publications in the period 1965–1969). Sadly Léon Tison suffered a stroke in November 1970, when he was about to leave home to travel to New Zealand to participate in a symposium on Representative and Experimental Basins. His ill health threatened the very existence of the association.
When Tison was forced to relinquish his position, it became obvious that
because of the increasing workload and concurrent thrusts in hydrology, as
well as the new ideas about the grouping of the water sciences, the
association needed a change. Consequently, a revised set of Statutes and
Bye-laws was brought into force at the Moscow General Assembly in 1971,
including a change in the name to the
A new management structure was devised to cope with the increasing number of
activities and the growing work load. A treasurer and an editor were
appointed to operate alongside the secretary general. Annual meetings of the
bureau of the association were instituted at this time, and more frequent
meetings were held between the president and secretary general. An editorial
office – later named the
Another major development in the period 1971–1981 was the reorganization of the scientific structure of IAHS. This had to be enhanced because of the considerable progress that had been made in the analysis of hydrological processes. Before that, many basic questions could only be answered by applying semi-empirical approaches. Better understanding and a more sophisticated and a higher conceptual level were reached by the application of system analyses, stochastic methods and analysis of time series. These techniques of applied mathematics had been developed at least two decades earlier, but it took a long time before they became part of hydrological practice. The term “parametric hydrology” came into being. A “Committee on Mathematical Models” was set up, which later received the status of “Commission on Water Resources Relations and Systems”. The title indicates that the field of work had been broadened. Likewise, the scope of the “Geochemical Commission” was changed during the Moscow Assembly in 1971, reflected in the new name “Commission on Water Quality”.
When the IHD ended in 1974, the IAHS was one of the bodies that helped in the
establishment of the permanent
Generally, the development of hydrology after 1970 became heavily influenced by the emergence of computers. Hydrological modelling, first in the form of lumped, conceptual models, changed the scene. Later, the more computer-demanding so-called physically based hydrological models appeared. Since that time the hydrological science, like most other sciences, has developed with ever-increasing speed.
Brant Broughton gauging station, UK. Source:
During the 1980s, environmental change and particularly climate change became more prominent on the research agenda. The development of improved global circulation models seemed a dominant trend, but for hydrologists their inability to simulate the hydrological cycle with any degree of verisimilitude, and the difficulties of incorporating land–atmosphere relations in them, were considerable impediments to progress. This was frustrating, because the increased power of computers and the advent of PCs provided opportunities in hydrology to simulate hydrological systems to a much higher degree of accuracy than before. These opportunities were stimulated by the development of new sensors on the ground and on satellites, to the extent that remote sensing became an important tool for hydrologists.
In response to these developments, IAHS started its own series of scientific assemblies, the first being held in Exeter in 1982. The assembly attracted over 500 participants, and the proceedings were published in six volumes, with nearly 1800 pages. For the Hamburg IUGG General Assembly in 1983, in contrast to the 1970s, the associations in the IUGG were able to arrange their own programmes within the assembly, and the IAHS attendance and programme benefited considerably as a result. Later during this period, the number of committees in IAHS was increased, and the joint IAHS/WMO GEWEX (Global Energy and Water Exchange) Committee was established. Both of these actions resulted from the widening of the role of the association in response to the scientific challenges arising. The purpose of the GEWEX Committee was in particular to establish a visibility and role for hydrologists in the burgeoning field of large-scale hydro-meteorological field experiments.
In 1981, the association, in cooperation with UNESCO and WMO, started the
annual award of a silver medal, known as the
In 1983, the name of the bulletin was changed to the
Specialized symposia continued to be organized by the commissions and
committees of the association, independent of general assemblies and
scientific assemblies, to the extent that in the early 1990s, seven or eight
Intense debates took place within the association around 1990. It was contended that water resources management, and in particular flood frequency modelling, should not be considered part of hydrology. This contention was opposed by other hydrologists, who pointed to the many achievements emerging from engineering approaches in hydrology. To limit hydrology to a pure geophysical science would be unreasonable and harm the association. No one really won the argument, and the disagreements were eventually reconciled. What was left by the crusade was a strengthening of the links between hydrology and geophysics.
Probably the most important IAHS initiative in support of the transfer of
knowledge to developing countries was started in 1991, when the association's
“Task Force for Developing Countries” (TFDC) commenced the mailing of
Two other heated debates within the association took place around the new millennium. One subject that involved much emotion was the wish of the glaciological community to leave IAHS in favour of a new cryosphere association within the IUGG. Snow and ice are integral parts of the hydrological cycle, and for that reason there was strong opposition in IAHS to accepting the new association. Again a compromise was achieved, which encompassed both a new glaciological association, the International Association of Cryospheric Science (IACS), in parallel to IAHS and a restructured commission on snow and ice hydrology within IAHS. Another subject was the suggestion that the commission structure should be abandoned and substituted by a purely project-driven organization. This was strongly contradicted by many hydrologists, who, among other things, pointed to the benefit of the many symposia organized by the commissions and working groups. No one could deny that a project structure might attract young hydrologists and revitalize the association, but it should not be at the expense of the advantages provided by the commissions. In the end, a compromise was achieved leading to a cross-cutting decadal project on prediction in ungauged basins, named PUB.
At present, there are few continuous flow records for most of the world's rivers. Where these measurements are made, they are subject to measurement errors, particularly during floods and droughts, the records can be short and interrupted, the calibration of the gauging stations can be poor and old records are often lost. River gauging is subject to cutbacks in government funding and is vulnerable to strife. However, reliable knowledge of flow and other hydrological variables is vital for planning and operating water resources projects, for flood forecasting and prediction, combatting water pollution and a host of other purposes. Such knowledge is the very basis of sustainable development.
The continued lack of comprehensive understanding about what happens to the rain at the catchment scale when it hits the ground surface has led to a plethora of models being developed and used for predicting runoff. These models differ markedly in their model concepts and structure, their parameters, and the inputs they use. They also differ in terms of which dominant processes they represent and the scales at which they make predictions. Most models are developed by different individuals and groups, with different disciplinary backgrounds; they benefit from local observations, experiences and practices that are influenced by local climate conditions and catchment characteristics. Consequently, they tend to have unique features not applicable in other places: every hydrological research group around the world seemingly studies a different object, their local catchment. The net result has been considerable fragmentation, “a cacophony” and a dissipation of effort that is not conducive to further advances.
In this context, the IAHS Decade on Predictions in Ungauged Basins was launched in 2003, aimed at achieving major advances in the capacity to make predictions in ungauged basins, through harnessing improved understanding of climatic and landscape controls on hydrological processes. The vision of PUB was to help a transformation “from cacophony to a harmonious melody”. One of the clear tasks that the PUB initiative set out to achieve was to address the fragmentation of modelling approaches through comparative evaluation: “classify model performances in terms of time and space scales, climate, data requirements and type of application, and explore reasons for the model performances in terms of hydrological insights and climate-soil-vegetation-topography controls.”
The decade was a great success in giving new momentum to IAHS. It attracted
many young researchers around the world and created a forum for cooperation
of the commissions. It succeeded in developing models to better predict
availability of water in diverse climatic and economic circumstances and
water-use settings, and to better forecast and predict floods and droughts in
basins and regions in which there has been little or inadequate data on which
to base models. The PUB decade resulted in three major publications: a review
summary article in HSJ, “A decade of Predictions in Ungauged Basins (PUB) –
A review” (Hrachowitz et al., 2013), and two books,
Given the role of the IAHS as a leader in international hydrology, a new
series of
The success of the PUB decade made a follow-up essential. Consequently, IAHS launched, for the period 2013–2022, a new scientific decade entitled Panta Rhei – Everything Flows (Montanari et al., 2013). The initiative is dedicated to research activities on change in hydrology and society. The purpose of the Panta Rhei initiative is to reach an improved interpretation of the processes governing the water cycle by focusing on their shifting dynamics in connection with rapidly changing human systems. The practical aim is to improve our capability to make predictions of water resources dynamics to support sustainable societal development in a changing environment. The concept implies a focus on hydrological systems as a changing interface between environment and society, whose dynamics are essential for determining water security, human safety and development, and for setting priorities for environmental management. The Panta Rhei scientific decade will devise innovative theoretical blueprints for the representation of processes including change and will focus on advanced monitoring and data analysis techniques. An interdisciplinary path will be sought by bridging with socio-economic sciences and geosciences in general.
The Panta Rhei decade has three clear objectives:
The continuous fall in the number of river flow gauging stations and the decline of precipitation networks are challenging in hydrology. To circumvent this, new observational methods based on advanced technology are entering the scene. There is growing use of remotely sensed data from satellites, aircraft surveillance, weather radar and now from unmanned aerial vehicles (UAVs, i.e. drones). This trend will continue and is expected to provide new opportunities to hydrologists.
From 2014, IAHS, UNESCO and WMO decided to award two international prizes
each year in place of the International Hydrology Prize; these were denoted
the
With the success of the updated IAHS website and online news, the free
Flow measurements using a drone. Flight campaign by Sune Yde Nielsen, Henrik Karmisholt Grosen (Drone Systems.DK), Christian Josef Köppl and Filippo Bandini (DTU Environment).
The IAHS Bureau governs the association; it consists of the president, the president-elect or immediate past president, three vice presidents, the secretary general, the treasurer, the editor-in-chief and presidents of the scientific commissions in existence at the time, as well as the chair of the International Association of Hydrological Sciences Limited. The final authority of the association in all matters of administration and finance is vested in the plenary administrative session of the association. It consists of the above persons plus one voting delegate from each adhering country. The company IAHS Ltd. deals, i.a., with the IAHS publishing programme, including the arrangements for the scientific journal. IAHS offers free membership and has currently 7000 members distributed throughout almost 200 countries.
With the activities of 10 commissions, 4 working groups and an ongoing,
vibrant scientific decade, Panta Rhei, IAHS is in excellent shape. The
commissions and working groups are as follows:
International Commission on Surface Water (ICSW) International Commission on Groundwater (ICGW) International Commission on Continental Erosion (ICCE) International Commission on Snow and Ice Hydrology (ICSIH) International Commission on Water Quality (ICWQ) International Commission on Water Resources Systems (ICWRS) International Commission on the Coupled Land-Atmosphere System (ICCLAS) International Commission on Tracers (ICT) International Commission on Remote Sensing (ICRS) International Commission on Statistical Hydrology (ICSH) IAHS Working Group on Panta Rhei (everything flows) IAHS Working Group on Education in Hydrology IAHS Working Group on MOXXI (Measurements & Observations in the 21st Century) IAHS Working Group on CandHy (Citizen and Hydrology).
The work of the IAHS Task Force for Developing Countries continues. Hydrology
in Wallingford takes care of the peer-review process of HSJ (which now has 3
co-editors and 48 associate editors) and its publication in partnership with
the publishing company Taylor & Francis; the administration of the
proceedings series (PIAHS), published by Copernicus; and provides support to
the Bureau, maintaining the IAHS website (
The International Association of Hydrological Sciences is a coherent and
well-integrated organization across all its different activities. Perhaps
this is the reason why the wisdom of changing from “science” to
“sciences” in 1971 has recently been challenged. Hydrology is today a
well-defined science in its own right and not a collection of different
sciences. A discussion is ongoing, and perhaps we will soon see a renaming of
the association to, for example,
The authors declare that they have no conflict of interest.
This article is part of the special issue “The International
Union of Geodesy and Geophysics: from different spheres to a common globe” (
The contributions to the IAHS history by Arthur Askew, Henny Colenbrander, Christophe Cudennec, Pierre Hubert, Hubert Savenije, the late Adriaan Volker, Frances Watkins and Gordon Young are greatly acknowledged. Thanks are also due to the large number of hydrologists who have aided and promoted the association since its inception in 1922. The paper has been written with due consideration of Volker and Colenbrander (1995), Rodda (1999, 2012) and Cudennec et al. (2013). Edited by: Jo Ann Joselyn Reviewed by: one anonymous referee