Hydrologic Cycle & Forest Hydrology Notes & Answers
Candace Lutzow-Felling for Blandy Bay Academy 2012
SLIDE 1 TITLE SLIDE.
Learning goal: to understand the role of trees and forests in the water cycle
Water: essence of life
Availability determines where and how animals and plants exist on Earth
SLIDE 2. FOREST HYDROLOGY
Hydroecology: study of the interface between the hydrologic cycle and life sciences;
plant-water interactions; ecohydrology
Influence is bi-directional; involves feedback mechanisms; trees influence the water cycle
& the water cycle influences trees
Forest hydrology: a sub-field of ecohydrology; how trees influence the hydrologic cycle
in forest ecosystems
Hydrology is an interdisciplinary science that includes
 Chemistry: chemical properties of water and interactions with the environment
(including the biota)
 Physics: movement of water through the hydrologic cycle (gravity and E
absorption and transfer)
 Geology: water storage; water movement; soil dynamics
 Environmental Science/Ecology: interactions with biotic and abiotic
components
 Biology: intake, use and outflow of water from organisms
SLIDE 3. HYDROLOGIC CYCLE
Hydrologic cycle synonym = ___water cycle_____________________________
Hydrologic cycle definition: __the process by which water moves through the
Earth’s atmosphere, land surface (including rivers, lakes, and groundwater),
oceans, and subsurface_______________________
What is the source of energy and the main force that drives the hydrologic cycle?
Energy __solar______________
Force__gravity____________
What does FLUX mean? _change in water from one area to another________
SLIDE 4. GLOBAL WATER BUDGET
Water budget is a tool to quantify the water cycle; the rates of movement and change in
water storage in all or parts of the atmosphere, land surface, and subsurface.
What is the MAIN important factor to understand about the global water budget?
The total amount of water is constant.
Is there more precipitation over land or over the ocean? ocean
What is the ratio of precipitation over land to ocean? 1:>3
Why do you think there is more precipitation over the ocean than the land?
more ocean area on the earth/more water evaporating over the ocean
Water from the land to the ocean flows from these two sources land surface & rivers
& groundwater
Which source has the greater quantity of flow into the ocean? land surface
Does precipitation over land equal evaporation from the land? NO
If this land P/E cycle continues, what would happen to the land water budget?
There would be a net deficit.
What keeps the land water budget in balance? Evaporation from the ocean; this
water is moved over the land by air currents (advection).
SLIDE 5. FLUXES OF WATER
How does water move in the hydrologic cycle (what are the processes)?
How does water move from the atmosphere to the land? precipitation
How does water move from the land or body of water to the atmosphere? evaporation
from the ground to vegetation root uptake
from vegetation to the atmosphere transpiration/evaporation
from land to ocean rivers/groundwater/run-off
from ocean to land evaporation & advection
from earth’s surface to below ground infiltration/percolation
from below ground to vegetation uptake
within the ground groundwater flow
overland stream flow/sheet flow
This movement of water from one portion of the hydrologic cycle to another is called
flux.
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SLIDE 6. WHERE DOES WATER RESIDE ON EARTH?
All water of Earth resides in three compartments of the hydrologic cycle:
Earth’s water
Water
Atmosphere
Unconsolidated
particles
clouds
Land
rivers
lakes & ponds
groundwater
ice: glaciers
Oceans
liquid
solid (ice)
Diagram 1. Paolo D`Odorico, ecohydrologist, water compartments or
apportionment
Earth’s water
Atmosphere
clouds
Unconsolidated particles
Land Surface
rivers
lakes & ponds
oceans
ice
glaciers
Arctic ice
Subsurface
soil
groundwater
Diagram 2. USGS water compartments or apportionment: atmosphere, hydrosphere,
lithosphere
Where is water stored on Earth? What are the NATURAL reservoirs or water
storage areas? For each water reservoir, what is the main phase of water that is
stored?
1. lakes & ponds (liquid)
5. rivers (liquid)
2. ocean (liquid
6. plants & animals & microbes (biota) (liquid)
3. ground water: aquifers (liquid) 7. soil (liquid)
4. atmosphere (gas)
8. glaciers (ice)
Where do we find water stored as ice? oceans (arctic ice) & land (glaciers)
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SLIDES 7-12. FORESTS & DEFORESTATION IMPACTS
Example illustrating the hydrologic connection between upland forests and the ocean
Why are forests so important when studying the hydrologic cycle?
1. Forests occupy about 1/3 of the earth’s land area
2. Tree leaves account for >2/3 of the leaf area of land plants; therefore, play a very
important role in terrestrial hydrology
SLIDE 13. PARTS OF A TREE
What are the main parts of a tree involved in the cycling of water?
1.crown
2. leaves 3. roots
4. branches 5. trunk 6. vascular tissue
SLIDE 14. FOREST CANOPY
How does the forest canopy interact with the water cycle?
1. intercepts precipitation 2. promotes condensation
3. changes drop size & reduces velocity
SLIDE 15. LEAF LITTER
Why is leaf litter important to the hydrologic cycle?
1. increases infiltration
2. slows overland flow
(also traps sediments & sequesters nutrients)
SLIDE 16. DEFORESTATION IMPACTS
What are the major consequences of removing the forest canopy?
1. rain drops are not intercepted 2. erosion
SLIDE 17. RAIN SPLASH
What can happen during a precipitation event when the canopy & leaf litter is
removed?
rain drop velocity is not decreased, rain quantity is not reduced (from interception), &
soil particles can become detached
SLIDE 18. EROSION
Rain splash over a large area can have these impacts downstream in a watershed:
1. sedimentation (turbidity)
2. siltation (sediment deposited in lakes & rivers)
3. water quality decreases
4. water storage capacity decreases
SLIDE 19. TREE ROOTS
Three ways that roots impact the soil ecosystem are:
1. stabilize the soil components & stream banks
2. increase infiltration
3. draw water from deep in the soil
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SLIDES 20-21. DEFORESTATION: Impacts on watersheds.
Cutting or removing trees from an ecosystem can result in this series of events during a
heavy rainstorm:
1. increase water flow
2.increase erosion
3increase sedimentation
Example of large-scale slope erosion after a heavy rainfall.
Propose a landslide risk management strategy for this mountainous region.
SUMMARY
Why are forests so important when studying the hydrologic cycle?
1. SCALE. Forest occupy about 1/3 of the earth's land area.
2. LEAVES. Tree leaves account for > 2/3 of the leaf area of land plants; therefore, they
play a very important role in terrestrial hydrology. Leaves also can impact local humidity
levels.
3. ROOTS. Extensive root systems stabilize soil. They affect water movement in soil
through the capillary process.
4. VASCULAR SYSTEM. This system creates a soil-plant-atmosphere continuum
moving large amounts of water from the soil though the plant and into the atmosphere.
5. CANOPY. Intercepts precipitation
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