Hydrology 1

Vocabulary flashcards summarizing principal terms and definitions from the hydrology lecture notes.

Hydrologic Cycle

The continuous movement of water through evaporation, condensation, precipitation, infiltration, runoff, and return to the atmosphere, driven primarily by solar energy.

Precipitation

Any form of water—liquid or solid—that falls from the atmosphere to the Earth’s surface, including rain, snow, sleet, and hail.

Surface Runoff

Water from precipitation that flows over land surfaces toward streams, rivers, or other bodies of water rather than infiltrating the ground.

Infiltration

The process by which water on the ground surface enters the soil, governed by soil voids, moisture content, and hydraulic gradients.

Groundwater Flow

The subsurface movement of water through aquifers driven by hydraulic gradients.

Hydrologic Budget (Water Balance)

An accounting of all water inflows, outflows, and changes of storage within a system or watershed.

Hydrology

The science that studies the occurrence, movement, and properties of water on and beneath the Earth’s surface.

Hydraulics

The branch of engineering dealing with the mechanical properties of liquids and the application of fluid mechanics to practical problems such as water supply.

Areal Rainfall

Average precipitation depth over a specified area, estimated from point rainfall measurements by methods such as Thiessen, Isohyetal, or Reciprocal Distance.

Thiessen Polygon Method

An areal rainfall estimation technique that assigns weights to rain-gauge data based on the area of polygons constructed around each gauge.

Isohyetal Method

A technique for estimating areal rainfall by drawing contours of equal precipitation (isohyets) and averaging the rainfall between successive contours.

Reciprocal Squared Distance Method

A weighting approach that estimates areal rainfall where each gauge’s influence is inversely proportional to the square of its distance to the point of interest.

Rainfall Intensity

The rate at which rain falls, commonly expressed in millimetres per hour (mm hr⁻¹) or inches per hour (in hr⁻¹).

Terminal Velocity (Raindrop)

The constant speed a falling raindrop attains when gravitational force equals air resistance, increasing with drop diameter.

Return Period (Recurrence Interval)

The average time, in years, between events equalling or exceeding a given magnitude, calculated as T = (n + 1)/m.

Partial Duration Series

A frequency-analysis approach that uses all events above a chosen threshold in the record, allowing multiple values per year.

Specific Humidity (qᵥ)

The mass of water vapor per unit mass of moist air, often expressed in kg water / kg moist air.

Vapor Pressure (e)

The partial pressure exerted by water vapor in a mixture of gases, independent of other gaseous constituents (Dalton’s Law).

Saturation Vapor Pressure (eₛ)

The maximum vapor pressure that can exist at a given temperature when the air is saturated with water vapor.

Relative Humidity (RH)

The ratio of actual vapor pressure to saturation vapor pressure at the same temperature, expressed as a percentage.

Dew-Point Temperature

The temperature to which air must be cooled at constant pressure to reach saturation (RH = 100 %).

Evaporation

The process by which liquid water becomes water vapor at temperatures below boiling.

Transpiration

The release of water vapor from plant surfaces through stomata during metabolic processes.

Evapotranspiration (ET)

The combined water loss from a surface due to evaporation and plant transpiration.

Potential Evapotranspiration (PET)

The evapotranspiration rate that would occur if water supply to the surface were not limiting.

Latent Heat of Vaporization (Lᵥ)

The amount of energy required to convert unit mass of liquid water to vapor without temperature change (~2.45 MJ kg⁻¹ at 20 °C).

Psychrometric Constant (γ)

A constant (~0.066 kPa °C⁻¹) describing the relationship between temperature and vapor pressure used in evaporation formulas.

Energy Balance Method

An evaporation estimation approach that relates net radiation to latent heat required for vaporization: Eₑ = Rₙ / (ρₚLᵥ).

Aerodynamic Method

An evaporation estimation technique using wind speed and vapor pressure gradient: Eₐ = B(eₛ − e).

Priestley–Taylor Method

A simplified combined approach estimating evaporation as E = 1.3 (Δ/(Δ + γ)) Rₙ / (ρₚLᵥ).

Class A Evaporation Pan

A standardized U.S. National Weather Service instrument (1.21 m diameter, 0.25 m deep) used to measure open-water evaporation.

Condensation

The change of water vapor to liquid water when air becomes saturated and cools below the dew point.

Sublimation

The direct phase change of water from solid (ice/snow) to vapor without passing through the liquid state.

Deposition (Frost)

The direct phase change of water vapor to solid ice crystals without becoming liquid, forming frost or snow.

Hydrologic Void Ratio

The ratio of the volume of voids (air + water) to the total volume of soil, affecting infiltration capacity.

Terminal Velocity Equation

Relationship showing that raindrop terminal velocity increases with diameter due to balancing gravity and drag forces.

Hydrologic Gauge Network

An arrangement of rainfall or stream gauges designed to measure spatially distributed hydrologic variables across a watershed.

Hydrologic Water Distribution

The partitioning of Earth’s water among atmospheric, surface, subsurface, and biological reservoirs.

Bose–Einstein Condensate (Water Context)

A state of matter mentioned as the fifth state, theoretically reached near absolute zero, unrelated to hydrologic cycling but noted for completeness.