Hydrology – The Meta-Science

Hydrology is the science of sciences.

There is no science that is as dependent on the other sciences and there is no science that is so fundamental to every other science. In fact, it is rarely the case that you would find a dedicated department of hydrology in any university, yet some aspects of hydrology are taught in almost every science department at every university.

Water is the base of measurement that is relied on in many fields of study.

Water defines the increment used for the Celsius scale at exactly 1/100 of the difference between the freezing and boiling points of water. The unit kelvin is defined as 1/273.16 of the thermodynamic temperature of the triple point of water. Water is the base for measurements of volume in SI units (one kg water = one liter) hence, water is used to define unit density, an important concept in physics. In geophysics, mean sea level is used as the datum for reference of all measurements at or near the Earth’s surface.

Water is fundamental to the lore of science.

The discovery of the Archimedes principle, which is fundamental to fluid mechanics and is the basis for modern aerodynamics, occurred while Archimedes was in the bath leading to the famous story of him running naked through the streets yelling Eureka! This was not the first, nor the last instance of water being the cornerstone of a new field in science.

Take geology for instance, the theory of plate tectonics transformed geology from a descriptive science into an explanatory science. The origin of the theory of plate tectonics is in the common knowledge that water flows downhill. Alfred Wegener struggled to reconcile this obvious truth with observations of fossils of water dwelling creatures in high mountains. It took many investigations over many years to prove his theory of continental drift, but it all started from the conundrum of water-borne sediments being discovered in places that defy the basic principles of water flow.

The atmosphere is a fluid and therefore meteorology is based on equations developed in the study of hydrology. The role of water in the study of meteorology is so profound that the term ‘atmospheric river’ is now used to describe an intense band of moisture, typically 400 to 600 km wide, which results in severe and sustained storm events. Both quantity and phase of water are important in predicting severe weather. Public perception of weather forecasting skill is lowest when temperature and pressure are near the triple point of water, where small error in one or the other variable is highly impactful on whether the resulting weather will be dry, snow, sleet, hail, or rain.

The greenhouse gas effect of water is variable. There is both a positive and a negative feedback to water’s role in the atmosphere. Water accounts for about 60% of the greenhouse warming effect, but because water is condensable, it does not control Earth’s temperature. Instead both the quantity and phase of atmospheric water is controlled by atmospheric temperature and pressure. As well as being a greenhouse gas, atmospheric water, especially in the solid phase, reflects sunlight, reducing the energy that reaches the Earth’s surface. Every other chemical in the composition of the atmosphere is highly predictable in terms of its quantity and state. The real skill in climatology is in predicting the ocean-land-atmosphere-biosphere-cryosphere exchange of water in all of its forms. In other words, climatology skill comes from understanding hydrology.

Water is the strangest chemical in the universe.

It expands when it freezes. This is why we have soil: water seeps into cracks in rocks, freezes, expands, and very systematically breaks rock into soil. Because frozen water is less dense than liquid water, it floats on the surface. If ice sunk, it would not be exposed to the sun or the atmosphere and the earth would very quickly turn into an ice ball. Instead, water under the ice provides refuge allowing life to survive through many ice ages.

Water enables the chemistry that is the basis of life.

Water is a universal solvent — the strange chemistry of water means that it can carry almost any substance or element either in suspension or in solution. Water enables multi-cellular life: every living multi-cellular organism is, essentially, nothing more than an elaborate system of tubes that use water to carry essential nutrients where they are needed and to remove metabolic waste from where it would other accumulate to toxic levels.

Whereas other sciences can trace their roots to the science of water, the science of water is also highly dependent on many other sciences.

Every hydrologist needs to be well versed in physics, chemistry, biology, geology, meteorology, climatology, geomorphology, math and statistics, fluid mechanics, soil science, and ecology. There is no other science that is as fundamentally inter-disciplinary as hydrology.

An understanding of basic principles of water flow allows me to better understand everything from traffic jams, to coffee percolation, to rocket science. Water is a substance that provides ample opportunity for discovery whichever discipline you come from or whatever problem you wish to solve.

Photo credit: U.S. Geological Survey  |  Building an ideal hydrologic technician

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