EESC/GEOG 205 - Hydrology Terms

hydrological cycle

the global-scale, endless recirculatory process linking water in the atmosphere, on the continents, and in the oceans

solar energy

driving force of hydrological cycle, specifically water vapor formation and transport

infiltration

the movement of rain or melted snow into the soil at the earth's surface

infiltration capacity

the maximum rate at which water can infiltrate the soil

percolation

The process by which water moves downward in the soil, toward the water table (porous soil and rocks)

evaporation

the physical process involving a phase change from liquid to vapor by which water is returned to the atmosphere

potential evaporation

the maximum rate of evapotranspiration from a vegetated catchment under conditions of unlimited moisture supply

transpiration

Evaporation of water from the leaves of a plant

surface runoff

water from rainfall or snowmelt that runs over the surface of the earth in sheets, rivulets, streams, and rivers

precipitation

the dominant process by which water vapor in the atmosphere is returned to the earth's surface either as liquid drops (e.g., rain) or solid particles (e.g., snow) under the influence of gravity

precipitation intensity

a measure of the rate of precipitation, commonly computed for a specified duration

interception storage

the process by which precipitation (either liquid or solid or both) is temporarily stored either on vegetation surfaces (canopy interception) or on litter surfaces (litter interception); intercepted water either can return to the atmosphere as evaporation or can become stemflow or throughfall

conservation of mass

the volume of a compartment is the difference of the inflow and outflow

water budget

Balance between the rates of water added and lost in an area

steady-state

inputs = outputs

runoff ratio

the ratio of average annual surface runoff to average annual precipitation for a given land area

dryness index

value is low = ratio: low PET to large water supply; value is high = ratio: high PET to limited water supply

budyko

EI(vap) = ET/P

catchment (or watershed)

an area of land, bounded by a divide, in which water flowing across the surface will drain into a stream or river and flow out of the area through a specified point on that stream or river.

vapor pressure

the actual partial pressure exerted by a vapor within an air mass; related to the concentration of water vapor in air

saturated vapor pressure

in a system in which both liquid water and water vapor are present, the partial pressure exerted by the water vapor during an equilibrium condition in which the rates of vaporization and condensation are equal; the saturated state of air increases as a non-linear function of air temperature

rain shadow effect

Precipitation falls on the windward side of a mountain range, resulting in lush vegetation & a warm, moist climate on one side, but a desert area on the leeward side.

orographic effect

The precipitation that occurs when moist air rises up the side of a mountain

continentality

the difference between marine and continental areas

hyetograph

a graph of precipitation vs time

isohyetal method

estimate mean precipitation over an area by drawing lines of equal precipitation

frequency analysis

a statistical technique used by hydrologists for estimating the average rate at which floods, droughts, storms, stores, rainfall events, etc., for a specified magnitude recur

exceedance probability

the probability that an event of a given magnitude will occur in a given year

return period

a measure of how often (on average) an event (precipitation, flood, etc.) will occur that is greater than some chosen value, the inverse of the exceedance probability

residence time

a measure of the average time a molecule of water spends in a reservoir.

residence time

defined for steady-state systems is equal to the reservoir volume divided by the inflow or outflow rate

Tr

storage size or volume of water / flow or flux (input or output)

intensity-duration-frequency analysis

relates rainfall intensity with its duration and frequency of occurrence

stemflow

precipitation that runs down the trunk or stem of a plant to reach the ground

throughfall

that portion of gross precipitation that is not held in storage by interception; it is also the precipitation that directly falls from the leaves to reach the ground

evapotranspiration

the sum of all processes by which water changes phase (from solid or liquid) to vapor and is returned to the atmosphere

penman equation

PET = change in net radiation + (psychometric constant (0.66 mb/ deg C) humidity gradient + windiness / (slope of sat vapor curve (mb/deg C) + psychometric constant (0.66 mb/ deg C)) latent heat of evap

actual evapotranspiration

the real rate of evapotranspiration from a land surface

surface energy balance

determine the amount of energy flux available to evaporative surface water and to raise or lower the temperature of the surface

latent heat of vaporization

the amount of energy per unit mass absorbed during a phase change from liquid to vapor at constant temperature; for evaporation of water at 0 deg C, it is 2.5 million Joules per kilogram of water

specific heat capacity of air

amount of heat that is required for something to change in temperature

sensible heat flux

H - the energy flux from surface to atmosphere carried by winds convection (the warmer the surface, the larger the heat flux)

latent heat

the portion of the internal energy of a substance that cannot be 'sensed' (i.e., is not proportional to absolute temperature); latent heat is the internal energy that is released or absorbed during a phase change at constant temperature

ground heat flux

the energy flux from surface to deep soil carried by conduction (direct contact) - tends to be small because not often bare soil

net radiation

incoming SW - outgoing SW + incoming LW - outgoing LW

saturated excess overland flow

a mechanism of runoff generation that is particularly important in vegetated catchments in humid regions in which a shallow water table intersects the ground surface, causing ponding of water at the soil surface and flow across the surface either in sheets or in small rivulets

infiltration excess overland flow

a mechanism of runoff generation in which the infiltration capacity of a catchment or a portion of a catchment is exceeded by the rainfall intensity, which results in ponding of precipitation at the soil surface and flow across the surface either in sheets or in small rivulets

groundwater

water found in the saturated zone of the subsurface

soil water

water that soaks into and collects in soil

saturated zone

a region of the subsurface where pores are completely filled with water and where water experiences a fluid pressure that is equal to or greater than local atmospheric pressure at the ground surface; the saturated zone is bounded at the top by the water table

unsaturated zone

a zone in a soil or rock between the earth's surface and the water table; pores in the unsaturated zone are partly filled with water and partly filled with air

river discharge

volume of water flowing through a river channel

discharge

the volume of flux of water

hydrology

the study of the occurrence and movement of water on and beneath the surface of the earth, the properties of water, and its relationship with the living and material components of the environment

recurrence interval

the interval between two events associated with a random variable attaining a value greater than some specified value

soil moisture

water that is held in soils and rocks under pressures less than atmospheric; water in the unsaturated zone

water table

a surface separating the saturated and unsaturated zones of the subsurface, defined as a surface at which the fluid pressure is atmospheric

Properties of water

very abundant, universal solvent, high cohesion, state of aggregation, thermal conductivity, electrical conductivity, transparency to EMR

Surface tension

water has a greater attraction internally than for air (high cohesive forces) but is affected by temperature

capillarity

suction due to surface tension & wetting

capillary fringe

layer where groundwater deeps up from the water table via capillary action to fill pores

density change of water

Increase density from 100C to 4C (water get colder)

density change of water

Decrease density from 4C to 0C (to become ice)

water temperature and oxygen content

Lower temperature = more oxygen

latent heat of vaporization

vaporization: 2256 (100C), 2469 (15C), 2511 (0C) - J/g

latent heat of sublimation

sublimation: 2846 J/g (0C)

latent heat of fusion

fusion: 335 J/g (0C)

specific heat

energy required to raise one unit mass of water through one unit of temperature

high specific heat capacity of water

cohesion

temperature and vegetation

Temperature cooler in vegetated areas because energy is put towards evapotranspiration instead of evaporation

relative humidity

amount of water in the air vs how much it can actually hold

cloud development

vapor condense on condensation nuclei to form tiny droplets (many droplets merge to be heavy enough to fall)

cloud properties

determined by number & size of particles, shape of ice crystals

droplet growth in clouds

main way that droplets grow within a cloud: collision & coalescence

cloud's liquid water content

range of droplet sizes

cloud thickness

thin cloud = less water

rain production

depends on updrafts (more updraft = more turbulence = more energy = less likely precip)

state of water at different temperatures in a cloud

Ice: < 0, Water: > -40, Supercooled: 0 to -20

Bergeron process

vapor pressure difference causes vapor molecules to move from liquid droplet to ice crystal (difference increase as temp decrease)

temperature profile for snow

temperatures consistently below 0

sleet and its temperature profile

freezing rain/drizzle and temperature profile

0 at 1/4 way down and go back to <0 right before reaching ground

ice pellets

same as freezing rain/drizzle but temp go back to <0 higher above ground level

hail and damage

opaque = freezing instant, transparent = freezing slow; agricultural & infrastructural damage

dew, frost & **** frost

air becomes saturated around a cooled surface, leading to condensation & deposition

mist & fog

low elevation clouds w/ same origin as dew; use as a water supply

fog drip

where water droplets in air stick to surfaces and can be harvested (normally missed by rain gauges)

rime

similar to fog drip, but its supercooled droplets that freeze on contact

cloud seeding

prevent hail damage by injecting enough nuclei to reduce size or induce precipitation

chemical composition of precipitation

depends on nuclei and aerosols (any solids or liquids suspended in atmosphere)

orographic lifting

air masses are forced up over topography and there's more precipitation on west side of mountain

frontal lifting

cold front - larger area, thunderstorms; warm front

convergent lifting

net horizontal inflow of air into a region - air converge at surface and is forced to rise

convectional lifting

normally occurs in areas with low pressure; very localized, associated with thunderstorms

manual precipitation measurement

manually measure depth of a bucket everyday at the same time

Rain gauge

must be put in clearings & usually only located in populated areas

Weighing gauge

measure total precipitation over a fixed time interval

Tipping bucket

measure number of tips per interval

surrogate measurement

Radar to measure precipitation; record time & intensity of reflection

satellite remote sensing

2 sensors - radar (size, type & volume) & microwave sensor (intensity)