L5. Interception and throughflow

Question 1

What is interception loss?

Answer 1

Proportion of precipitation that may be intercepted by a vegetation canopy and lost to the atmosphere via evaporation without reaching the ground

Question 2

What is the definition of interception?

Answer 2

Fraction of the gross precipitation input which does not reach the ground. Typically wets and adheres to above ground objects until it is returned to the atmosphere through evaporation.

Question 3

Define gross precipitation (P)

Answer 3

Precipitation that is measured above the canopy or in a clearing

Question 4

Define through-fall (T)

Answer 4

Precipitation reaching the ground directly or via canopy drip

Question 5

Define stemflow (S)

Answer 5

Water reaching the ground by flowing along tree trunks and plant steams

Question 6

Define total interception loss

Answer 6

Sum of all canopy interception and losses

Question 7

Define net precipitation (N)

Answer 7

Gross precipitation minus total interception loss

Question 8

Why is interception hard to measure directly during rainfall events?

Answer 8

Lots of spatial variability (vegetation density/type, wind, etc.). Lots of temporal variability since interception increase exponentially during a storm, until the interception capacity is achieved, and the weight of more rain overcomes the surface tension holding the water on the plants.

Question 9

What is canopy storage for conifers

Answer 9

1-2 mm per square meter

Question 10

What is canopy storage for deciduous trees?

Answer 10

less than 1mm per square meter

Question 11

What is canopy storage for tropical trees?

Answer 11

1-5mm per square meter

Question 12

What is canopy storage for grasses?

Answer 12

1-1.5mm per square meter

Question 13

Why is interception a critical hydrological process?

Answer 13

• Can be a significant water source for evapotranspiration
• has a strong influence on runoff
• canopy drip can increase local erosion

Question 14

What are 3 methods of interception measurements?

Answer 14

• above and below canopy (works in small areas but hard to get enough samples)
• plastic sheets (effective but doesn’t work over large areas and with snow)
• cantilever effect (accurate but would take way to long)

Question 15

How does precipitation intensity influence interception?

Answer 15

High intensity rainfall events can lead to water being delivered too quickly for the plants to accommodate whereas low intensity rain events can allow for more precipitation to be intercepted (new storage capacity is continuously created by ongoing drippage and stemflow)

Question 16

How does precipitation duration influence interception?

Answer 16

Most water from a short event can be interception (still dependent on intensity)

Question 17

How does precipitation frequency influence interception?

Answer 17

Long delays between consecutive events allow wet vegetation to dry out and more canopy storage to become available before the next storm

Question 18

How does wind speed influence interception?

Answer 18

Can promote interception loss by evaporation but could also increase interception by blowing water into the interior of plants and plastering wet snow against trees and shrubs

Question 19

How does precipitation type influence interception?

Answer 19

• If temp is below 0 rain can freeze to plants
• snow is more easily blown off plants than rain
• wet snow sticks to plants, and some snowflakes can bridge gaps between leaves resulting in considerable interception

Question 20

Define depression storage

Answer 20

gross precipitation or through-fall retained in puddles, stock ponds, ditches, and other depressions in the ground surface (can hold alot and make significant impact)

Question 21

Define wetlands

Answer 21

Transitional systems between terrestrial and aquatic systems where the water table is usually at or near the surface or the land covered by shallow water

Question 22

Criteria to determine wetlands (need at least 1 out of 3)

Answer 22

• at least periodically, the land supports predominantly hydrophytes
• the substrate is predominantly undrained hydric soil
• the substrate is saturated with water or covered by shallow water at some time during the growing season of the year

Question 23

What is the major hydrological benefit of wetlands?

Answer 23

They “trap” excess water in their depressions, leading to less runoff and less intense flooding

Question 24

What are the hydrologic conditions of wetlands?

Answer 24

Groundwater (water table) must be at the surface or with the soil root zone during all or part of the growing season

Question 25

What are hydric soils?

Answer 25

Soils that are saturated, flooded, or ponded long enough during the growing season to develop oxygen-free conditions in the upper 6 inches

Question 26

What is hydrophytic vegetation?

Answer 26

plants typically adapted to wetland and aquatic habitats, plants which grow in water or on a substrate that is at least periodically deficient in oxygen due to excessive water content.