Ren R 350 Midterm

• water balance
• energy balance

• usually year (1 complete annual cycle)
• avg. across many yrs

• usually the watershed
• nationally/globally

• P = ET + Q +/- change in storage
• P(+) + ET (-) + Q (-) + (+/-) change in storage = 0

topographically delineated aarea of land that collects and discharges surface stream flow through one outlet

evaporation, transpiration, interception

water held in the soil mantle of a watershed

• describe hydrology of area
• basis of understanding impacts of land use on hydrology

~ +/- 10-15% best that can be expected

form of electromagnetic energy from rapid oscillations of electromagnetic fields

0.15-3.0μ

3.0-100μ

• symbol: α
• reflected incoming shortwave radiation

• symbol: ε
• absorbed or emitted incoming shortwave radiation

= 1

emit high energy, shorter λ

emit lower energy, longer λ

Q* = (K↓) + (L↓) + K(↑) + (L↑)

Q* = Qh + Qg + Qe

• symbol: ρ
• like thermal capacity but mass-based (cal/g * °C)

• symbol: c
• volume based (cal/cm^{3 * °}C)

• symbol: k
• how easy it is for energy to travel through a substance (cal/cm * min * °C)

• conductivity * potential energy gradient
• (conductivity=1/resistance)

• = change in temperature/distance bw points
• = ΔT/ΔZ

• thermal capacity (ρC): energy req. to raise temp of substance by 1°C
• thermal conductivity (k): ease of heat transport thru substance

Qg = (ρC) * -k(ΔT/ΔZ)

• turbulent transfer coefficient (Kh) velocity term
• thermal conductivity of air (k)
• wind speed (μ)

Qh = (ρC) * -kh (ΔT/ΔZ)

mass transfer in slowly moving air currents, changes temperature only

• Qi
• energy used or released during phase changes of water (L)
• (-) means energy required, (+) means energy released

• driving force: vapour pressure gradient
• wind (μ) helps maintain VP gradient
• C = coefficient to regulate for diff. situations

• Qe = LV * μC (Δe/ΔZ)
• LV = latent heat of vaporization

Lf = 3.3x10⁵ J/kg

Ls = 2.79x10⁶ J/kg

Lv = 2.45x10⁶ J/kg

ET = Qe/Lv

• bodies emit radiation as a function of their temperature
• since the atmosphere is cold at night, and the earth is warm from the previous day, at night there is energy being emitted from the earth (Q* no longer incoming, but outgoing)

β = Qh/Qe

• means Qh<Qe
• evaporation dominates
• daytime, moist conditions, conversion of water and conditions are not moisture limited

• means Qh>Qe
• heat production dominates
• often nighttime, dry conditions

• before shower, sunny day
• after shower, evaporation of water on surfact needs energy, so steals energy from heat production
• therefore the surface becomes cooler than the atmosphere because of evaporation
• once evaporation is done, surface will warm up and Qh flux will cause Bowens ratio to go back to (-)

• ambient vapour pressure
• vapour pressure in air mass at current temperature

• saturation vapour pressure
• max amount of vapour pressure that can exist in air mass at ambient/specified temperature

• ambient temperature
• temperature right now, aka dry bulb temperature

• dew point temperature
• temperature where condensation occurs (es=ea)

• wet bulb temperature
• when evaporation decreases temperature, usually measured with a psychometer

RH = (ea/es) * 100

• VPD (KPa) = (es-ea)
• affected by temperature

peaks, ambient temp, lowest

• lapse rate for a parcel of air that rises or falls without any significant energy exchange with the surrounding atmosphere
• does not lose or gain any water or energy
• changes in temperature of the air are due only to changing volume with pressure

• when volume expands w/ less pressure as you go up higher, less interparticle collisions, therefore lower temperature
• moist situation: gaseous vapour going to condense if cooled
• releases energy
• cools less than dry process because of state change, condensation releases energy that warms

comparison of environmental lapse rate with that of the adiabatic lapse rate

existing (real) temperature profile with elevation that is present

the rate at which air masses cool as they rise because of changes in atmospheric pressure

• Ta<Te
• temperature profile that does not demand more rising of air
• bc rising air ALWAYS cools at the adiabatic rate

Ta>Te

• forced lifting caused by topography
• air masses cool when riding up over the land surface (increase in elevation=cooling)

• forced lifting, warm and cool air masses in collision
• often involves oceanic air masses

• cold air moving under warm air and pushing it up fast
• produces short and high intensity precip. events

• warm air going up over receding cold air
• produces long distance areas of low intensity precip.

• unstable atmospheres
• combination of forced lifting and unstable air

• undercatch and overcatch
• ↑wind speed = ↓effective catch area of gauge opening

• total P vs. time/intensity (mm/hr)
• remote location, expensive

recording, non-recording, installation

• total P/daily P, monthly, seasonal
• inexpensive, suitable for local use only

• single gauge vs. network of gauges
• considerations: $, line of sight, access

-5 to -80%

spatial variation, more

• avg. of point values
• not spatial average

• spatial weighting
• point value is assigned to entire polygon
• acounts for spatial distribution of precip. bw stations
• accounts for non-uniform station distribution

• spatial weighting
• linear/non-linear interpolations bw stations
• continuous gradient (surface) of precip.
• more spatial resolution than Thiessen polygons and accounts for variation in elevation

precipitation/unit time (mm/hr)

increases, decline

p = m/(n+1)

Tr = 1/p

peak annual (or instantaneous) discharge against Tr

snow depth x snow density x water density

• elevation
• wind
• slope and aspect

• low density
• crystal structure
• high albedo

• increase in density
• granular structure
• lower albedo

total loss of water from a snowpack by snowmelt plus evap/sublimation

amt of liquid water produced by melting of snow that leaves the snowpack

increase in snowpack temp to 0°C

measure of "energy" needed to raise the avg temp of a snowpack to the melting point

snowmelt increases the water content in snow, but no output from the bottom of the snowpack

water held against gravity on snow crystals and in capillary channels in snowpack

• once ripe, any additional melt will be output from the bottom of the snowpack
• percolation water water through snowpack
• infiltrates soil if it's thawed/porous

water and energy

Th + Sf

Ic = Pg - (Th + Sf)

Ic + Il

Pg - I

• max amt of water held in all aerial portions of the vegetation and in the litter
• bucket metaphor

• branch arrangement
• crown form
• bark form/roughness
• leaf habit
• crown density, crown length

• snow vs rain
• storm sizes and frequency

• gross precip. (Pg) in an open area
• throughfall precip (Th) under the canopy
• stemflow

I = Pg - (Th + Sf)

• troughs: increased surface area, less rain gauges
• roving rain gauges: relocate after each "event", increases statistical power

VPD = Δe = (es-ea) across some distance

= Cμ (es-ea)

mechanism to move water + supply of energy

• net radiation
• vegetation and litter
• water availability

Θg = (mass wet-mass dry)/(mass dry)

θv = (mass wet-mass dry)/(volume wet)

storage = θv x profile depth

Ψt = Ψg + (Ψp + Ψm)

water potential gradient