Ren R 350 Midterm

  1. 2 major approaches to quantifying hydrologic cycle?
    • water balance
    • energy balance
  2. hydrological scale: temporal
    • usually year (1 complete annual cycle)
    • avg. across many yrs
  3. hydrological scale: spatial
    • usually the watershed
    • nationally/globally
  4. Water balance eqn
    • P = ET + Q +/- change in storage
    • P(+) + ET (-) + Q (-) + (+/-) change in storage = 0
  5. watershed
    topographically delineated aarea of land that collects and discharges surface stream flow through one outlet
  6. 3 components of ET?
    evaporation, transpiration, interception
  7. storage
    water held in the soil mantle of a watershed
  8. application of water balance knowledge?
    • describe hydrology of area
    • basis of understanding impacts of land use on hydrology
  9. precision of water balance estimations?
    ~ +/- 10-15% best that can be expected
  10. radiation
    form of electromagnetic energy from rapid oscillations of electromagnetic fields
  11. shortwave (K) wavelengths
  12. longwave (L) wavelengths
  13. albedo
    • symbol: α
    • reflected incoming shortwave radiation
  14. emissivity
    • symbol: ε
    • absorbed or emitted incoming shortwave radiation
  15. α+ε = ??
    = 1
  16. radiation emitted by hot objects?
    emit high energy, shorter λ
  17. radiation emitted by cold objects?
    emit lower energy, longer λ
  18. net radiation eqn (2 versions)
    Q* = (K↓) + (L↓) + K(↑) + (L↑)

    Q* = Qh + Qg + Qe
  19. specific heat
    • symbol: ρ
    • like thermal capacity but mass-based (cal/g * °C)
  20. thermal capacity
    • symbol: c
    • volume based (cal/cm3 * °C)
  21. thermal conducitivity
    • symbol: k
    • how easy it is for energy to travel through a substance (cal/cm * min * °C)
  22. transfer rate eqn
    • conductivity * potential energy gradient
    • (conductivity=1/resistance)
  23. thermal gradient eqn
    • = change in temperature/distance bw points
    • = ΔT/ΔZ
  24. 2 thermal properties of ground heat (Qg)
    • thermal capacity (ρC): energy req. to raise temp of substance by 1°C
    • thermal conductivity (k): ease of heat transport thru substance
  25. conduction of Qg eqn
    Qg = (ρC) * -k(ΔT/ΔZ)
  26. factors involved with convection of sensible heat (Qh)
    • turbulent transfer coefficient (Kh) velocity term
    • thermal conductivity of air (k)
    • wind speed (μ)
  27. convection of Qh eqn
    Qh = (ρC) * -kh (ΔT/ΔZ)
  28. sensible heat
    mass transfer in slowly moving air currents, changes temperature only
  29. latent heat
    • Qi
    • energy used or released during phase changes of water (L)
    • (-) means energy required, (+) means energy released
  30. latent heat exchange (Qe) factors
    • driving force: vapour pressure gradient
    • wind (μ) helps maintain VP gradient
    • C = coefficient to regulate for diff. situations
  31. Qe eqn
    • Qe = LV * μC (Δe/ΔZ)
    • LV = latent heat of vaporization
  32. latent heat of fusion
    Lf = 3.3x105 J/kg
  33. latent heat of sublimation
    Ls = 2.79x106 J/kg
  34. latent heat of vaporization
    Lv = 2.45x106 J/kg
  35. evapotranspiration eqn
    ET = Qe/Lv
  36. in an energy flux density vs time diagram, why would the Q* line drop below 0 at night time?
    • 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)
  37. Bowens ratio
    β = Qh/Qe
  38. what does it mean if β<1
    • means Qh<Qe
    • evaporation dominates
    • daytime, moist conditions, conversion of water and conditions are not moisture limited
  39. what does it mean if β>1
    • means Qh>Qe
    • heat production dominates
    • often nighttime, dry conditions
  40. what happens during an oasis effect that changes the Bowens ratio from (+) to (-)
    • 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 (-)
  41. ea
    • ambient vapour pressure
    • vapour pressure in air mass at current temperature
  42. es
    • saturation vapour pressure
    • max amount of vapour pressure that can exist in air mass at ambient/specified temperature
  43. Ta
    • ambient temperature
    • temperature right now, aka dry bulb temperature
  44. Td
    • dew point temperature
    • temperature where condensation occurs (es=ea)
  45. Tw
    • wet bulb temperature
    • when evaporation decreases temperature, usually measured with a psychometer
  46. relative humidity eqn
    RH = (ea/es) * 100
  47. Vapour pressure deficit
    • VPD (KPa) = (es-ea)
    • affected by temperature
  48. relative humidity ____ when ____ is ____
    peaks, ambient temp, lowest
  49. Adiabatic lapse rate
    • 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
  50. why does a moist adiabatic lapse rate process become less cold than a dry adiabatic lapse rate process?
    • 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
  51. atmospheric stability
    comparison of environmental lapse rate with that of the adiabatic lapse rate
  52. environmental lapse rate
    existing (real) temperature profile with elevation that is present
  53. adiabatic rate
    the rate at which air masses cool as they rise because of changes in atmospheric pressure
  54. stable atmosphere?
    • Ta<Te
    • temperature profile that does not demand more rising of air
    • bc rising air ALWAYS cools at the adiabatic rate
  55. unstable atmosphere?
  56. orographic storms
    • forced lifting caused by topography
    • air masses cool when riding up over the land surface (increase in elevation=cooling)
  57. cyclonic and frontal storms
    • forced lifting, warm and cool air masses in collision
    • often involves oceanic air masses
  58. cold front
    • cold air moving under warm air and pushing it up fast
    • produces short and high intensity precip. events
  59. warm front
    • warm air going up over receding cold air
    • produces long distance areas of low intensity precip.
  60. convective storms
    • unstable atmospheres
    • combination of forced lifting and unstable air
  61. #1 error in recording precipitation
    • undercatch and overcatch
    • ↑wind speed = ↓effective catch area of gauge opening
  62. precipitation gauges: recording
    • total P vs. time/intensity (mm/hr)
    • remote location, expensive
  63. 3 types of precipitation gauges
    recording, non-recording, installation
  64. precipitation gauges: non-recording
    • total P/daily P, monthly, seasonal
    • inexpensive, suitable for local use only
  65. precipitation gauges: installation
    • single gauge vs. network of gauges
    • considerations: $, line of sight, access
  66. average error due to exposure/wind (undercatch) when measuring precip?
    -5 to -80%
  67. the more ______ in an area, the _____ gauges you need per km
    spatial variation, more
  68. arithmetic mean
    • avg. of point values
    • not spatial average
  69. Thiessen polygons method
    • spatial weighting
    • point value is assigned to entire polygon
    • acounts for spatial distribution of precip. bw stations
    • accounts for non-uniform station distribution
  70. Isohyetal analysis
    • 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
  71. intensity
    precipitation/unit time (mm/hr)
  72. as storm duration____, intensity tends to ______
    increases, decline
  73. probability eqn
    p = m/(n+1)
  74. return period eqn
    Tr = 1/p
  75. plotting flood frequency?
    peak annual (or instantaneous) discharge against Tr
  76. calculating SWE
    snow depth x snow density x water density
  77. influential factors of snow accumulation
    • elevation
    • wind
    • slope and aspect
  78. characteristics of new snowpacks
    • low density
    • crystal structure
    • high albedo
  79. characteristics of a mature snowpack
    • increase in density
    • granular structure
    • lower albedo
  80. ablation
    total loss of water from a snowpack by snowmelt plus evap/sublimation
  81. snowmelt
    amt of liquid water produced by melting of snow that leaves the snowpack
  82. warming phase
    increase in snowpack temp to 0°C
  83. cold content
    measure of "energy" needed to raise the avg temp of a snowpack to the melting point
  84. ripening phase
    snowmelt increases the water content in snow, but no output from the bottom of the snowpack
  85. liquid water holding capacity
    water held against gravity on snow crystals and in capillary channels in snowpack
  86. output phase
    • 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
  87. 2 conditions needed for evapotranspiration
    water and energy
  88. interception: amt reaching forest floor =
    Th + Sf
  89. interception: canopy interception =
    Ic = Pg - (Th + Sf)
  90. total interception =
    Ic + Il
  91. interception: net ppt =
    Pg - I
  92. interception storage capacity
    • max amt of water held in all aerial portions of the vegetation and in the litter
    • bucket metaphor
  93. vegetation controls on interception losses
    • branch arrangement
    • crown form
    • bark form/roughness
    • leaf habit
    • crown density, crown length
  94. Precipitation controls on interception losses
    • snow vs rain
    • storm sizes and frequency
  95. interception measurement done my measuring
    • gross precip. (Pg) in an open area
    • throughfall precip (Th) under the canopy
    • stemflow

    I = Pg - (Th + Sf)
  96. measuring throughfall (2 methods)
    • troughs: increased surface area, less rain gauges
    • roving rain gauges: relocate after each "event", increases statistical power
  97. driving force of evaporation
    VPD = Δe = (es-ea) across some distance
  98. E =
    = Cμ (es-ea)
  99. Penmen eqn is a combination of:
    mechanism to move water + supply of energy
  100. 3 factors affecting soil evaporation
    • net radiation
    • vegetation and litter
    • water availability
  101. gravimetric water potential
    Θg = (mass wet-mass dry)/(mass dry)
  102. volumetric water potential
    θv = (mass wet-mass dry)/(volume wet)
  103. total storage in a given soil profile
    storage = θv x profile depth
  104. total water potential eqn
    Ψt = Ψg + (Ψp + Ψm)
  105. driving force of soil water movement?
    water potential gradient
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Ren R 350 Midterm
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