Complete EESC/GEOG Hydrology 205 Final

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

DI = PET (demand for water (energy driven evap. demand)) / P (water supply available for ET)

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

precipitation intensity

Rate of precipitation over a specified time period

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. the 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. its 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

What is capillarity

suction due to surface tension & wetting

What is the capillary fringe

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

How does water change density as it changes states

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

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

How does water temperature affect oxygen content

Lower temperature = more oxygen

Latent heat of vaporization, sublimation and fusion

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

sublimation: 2846 J/g (0C)

fusion: 335 J/g (0C)

What is specific heat

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

Why does water have a high specific heat capacity

cohesion

How is temperature related to vegetation

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

Define relative humidity

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

How does cloud development occur

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

what are cloud properties determined by

phase of water

number & size of particles

shape of ice crystals

main way that droplets grow within a cloud

collision & coalescence

what does rain production depend on

cloud's liquid water content

range of droplet sizes

cloud thickness (thin cloud = less water)

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

electrical charge of droplets & electric field within cloud

State of water at different temperatures in a cloud (ice, water, supercooled)

Ice: < 0

Water: > -40

Supercooled: 0 to -20

What is the Bergeron process

water vapor grow at the expense of ice crystals

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

Ice has a lower vapor pressure than water

Temperature profile for snow

temperatures consistently below 0

Sleet & its temperature profile

rain + snow

<0 --> >0 halfway down

freezing rain/drizzle & temperature profile

supercooled rain that freezes on contact with cold surfaces

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

ice pellets

frozen rain/drizzle

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

Hail & damage it can cause

accretion of supercooled water on graupel, large frozen raindrop or other particle

opaque = freezing instant, transparent = freezing slow

agricultural & infrastructural damage

dew, frost & hoar frost

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

not significant part of hydrological cycle as it doesn't rly change catchment water balance

mist & fog; use as a water supply

low elevation clouds w/ same origin as dew

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

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

what is cloud seeding

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

chemical composition of precip 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

warm air forced up & over cold, denser air

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

normally occurs in areas with low pressure

convectional lifting

heat earth surface -> warm air rise -> cool air sink

very localized, associated with thunderstorms

Rain gauge

Measure precipitation (recording)

manually measure depth of a bucket everyday at the same time

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

capping/plugging

Weighing gauge

Measure precipitation (recording)

measure total precipitation over a fixed time interval

Tipping bucket

Measure precipitation (recording)

measure number of tips per interval

can get overwhelmed by high intensity precipitation

capping/plugging can be an issue

Radar to measure precipitation

surrogate measurement

record time & intensity of reflection

satellite remote sensing

surrogate measurement of precip

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

wind undercatch

wind turbulence at mouth of gauge result in not all precip getting collected

error increases with windspeed

error can be lessened using shielded gauges

methods of estimating precipitation over a drainage basin

1. arithmetic average (very inaccurate)

2. thiessen weighted average (when gauges not uniformly distributed or large precip differences within area)

3. isohyetal method: req a lot of data (lines of equal precip, measure area between isohyetes & calculate weighted precip)

Probability of exceedance & recurrence interval

how likely rainfall will exceed a certain amount

Intensity-Duration-Frequency (IDF) Analysis

how frequently we get a storm of a certain size & how long it rains at a high intensity

design storm drains, flood control structures, bridges etc.

impacts of land cover or management changes

Annual maxima series

identify the largest rain events each year at different durations

plot intensity vs duration for different return periods

essential factors for evaporation

energy supply, available water supply and a vapor deficit

define transpiration

phase change of liquid to gas occurring through the stomata

define potential evaporation

theoretical evaporation from a terrestrial surface if water supply is unlimited

measured using amt of ENERGY available to drive evaporation

equation for energy available for evap

Eevap = Qsn + Qln + Qh + Qg

Eevap: energy available for evap

Qsn: net SW radiation

Qln: net LW radiation

Qh: sensible heat flux (diff in temperatures)

Qg: soil heat flux