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Hydrology > Lecture Panel 5 > Flashcards

Lecture Panel 5 Flashcards

1
Q

What does water interception refer to?

A

water that never reached the ground

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2
Q

What things could happen to a raindrop falling in a forest?

A
  • throughfall (to the ground)
  • interception loss (canopy)
  • interception loss (stem) to stemflow
  • interception loss in leaf litter
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3
Q

What is Net Rainfall?

A

Net Rainfall = Gross Precipitation - Interception Loss

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4
Q

What is the hydrological significance of interception?

A
  • results in reduction of precipitation and transpiration
  • drop sizes are changed (larger under tree)
  • spatial variability of precipitation is changed (distribution on ground)
  • water chemistry is changed
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5
Q

How much precipitation does different foliage intercept and then lose to evaporation?

A

coniferous: 30-35%
deciduous: 15-25%
Tropical forest: 10-15%

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6
Q

What special adaptations do tropical forests have?

A

adaptations to move water to roots, eg. waxy leaves

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7
Q

What is the leaf area index?

A

-how much of a cylinder cross section would be covered by foliage (from ground up)

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8
Q

how much can a forest canopy store?

A

up to 25mm of precipitation in forests with multiple overlapping canopies

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9
Q

How does intensity affect interception?

A

lower intensity means higher interception

-high intensity overwhelms storage capacity of plants

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10
Q

how does precipitation duration affect interception?

A

-a large proportion of short duration precipitation is intercepted

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11
Q

How does wind speed affect interception?

A
  • blows precipitation further into trees, promoting interception
  • promotes evaporation as taller vegetation presents a rougher surface, thereby generating eddy convection necessary for vapour transport
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12
Q

How does precipitation type affect interception?

A
  • liquid water adheres readily due to surface tension

- snow is easily blown off, but sticky snow can accumulate greatly on branches

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13
Q

how does precipitation frequency affect interception?

A
  • there is only a certain amount of precipitation storage capacity
  • maximum interception occurs when there are short duration events with enough time for evaporation between them
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14
Q

What is horizontal interception by conifers?

A
  • needles act as condensation nuclei, intercepting water droplets in clouds
  • conifers have massive surface area which helps this
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15
Q

what is stemflow

A

water from leaves that gets sent down the stem to the roots

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16
Q

What intercepts precipitation in the arctic?

A

Shrubbery - 10% in sparse to 30% in dense

17
Q

What increases areal precipitation estimation?

A

density, time, and area

18
Q

methods for areal precipitation estimation

A
  • simple arithmetic average
  • thiessen polygons
  • isoheyetal method (line of equal water)
19
Q

What is the isoheyetal method?

A
  • most basic method of representing spatial distribution of rainfall
  • most accurate but most laborious method
  • locate all rain stations on a base map and record rainfall amount
  • draw lines of equal water by proportioning the distances between adjacent gauges according to different catch
  • calculate mean precipitation in each isoheyetal area
  • sum over all areas for average
20
Q

What is the inverse distance weights interpolation method

A
  • for any point you choose, you can use data from nearby gauges to extrapolate rainfall at that point, giving each gauge a weight based on distance that you choose
  • weight parameter is p, inverse exponent - set it large if you want far distances to have low weight
  • computer can help optimize p
  • user also can also set a distance limit for what points should be considered, and add directional preference for points
21
Q

Kriging

A
  • use semivariance between points on map for interpolation
  • asks “how well are points of a certain distance related to another point” (covariance)
  • could change temporally and directionally
22
Q

How can we compare interpolation models?

A

could leave out certain data points and see which one gets closer

23
Q

Spatial interpolation rules of thumb

A
  • the point values may contain error - determine sources of error and make corrections if necessary
  • don’t use a method that is more complicated than is warranted given the data quality
  • often the statistical criteria for the interpolation method are not valid given other spatial controls (eg. topography) on precipitation
24
Q

What methods try to account for topography effects on precipitation?

A
  • hysometric method - approximates the effects of topographic change on precipitation statistics (linear regression)
  • PRISM (parameter-elevation regressions on independent slopes model)
25
Q

What does PRISM use?

A
  • historic record of measured precipitation
  • geographic input, especially terrain
  • –prevailing wind direction, streamflow measurements
26
Q

How can we use gauges with PRISM?

A

to estimate the quantitative precipitation for a given event or time period

27
Q

hyetograph and hydrograph

A

hyetograph - rainfall intensity vs time
hydrograph - discharge vs time in a river, etc.
-obvious relation between these two

28
Q

Temporal representation of rainfall graph

A

cumulative rainfall hyetograph (aka rainfall mass curve) - summation of rainfall increments over time
-slope gives an idea of intensity

29
Q

What does the changing slope of a cumulative hyetograph mean?

A

changes in rainfall over time

30
Q

What are intensity-duration relationships? what are they good for?

A
  • self explanatory. they must be locally calibrated but applicable to global scale
  • yield straight line on log-log graph
  • eg McCallum model, I=kt^-n (k and n are location dependent constants)
  • good for predicting runoff
  • different types of storms have different slopes
31
Q

WHat are intensity-duration-frequency curves? What are they good for?

A
  • IDF curves are established for many regions. Statistical relationship between intensity corresponding to storm duration and frequency
  • helps when constructing a neighbourhood to withstand a 100 year storm, for example
32
Q

Probable Maximum precipitation

A
  • hypothetical concept
  • analytically estimated greatest possible depth of precipitation that is physically possible and reasonably characteristic over a geographical region at a certain time of year
  • defined wrt a given area, including estimates of of moisture inflow over the basin and the amount that could be precipitated
  • theoretical concept, hard to defend

Hydrology (10 decks)

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