• Dalton developed an empirical equation based on vapor pressure deficit and a wind function.

  Penman combined Dalton's method with energy balance to develop a combination method for evaporation.

  Monteith improved the Penman method by expressing the Dalton component in physical (deterministic) terms.

c. What is albedo? What is the albedo of the Amazon rainforest? What is the albedo of the Sahara desert?

• Reflectivity coefficient of a surface. Amazon, a = 0.07-0.15; Sahara: a = 0.3-0.6.

d. What is the difference between potential and actual evapotranspiration?

• Potential evapotranspiration occurs under an ample supply of moisture.

• Actual evapotranspiration occurs in reality, when moisture may be limited.

e. What are the typical upper and lower limits for stream slopws in nature?

• Upper limit: 0.10 and more in mountain streams

• Lower limit: as low as 0.000006 in tidal streams.

f. What is a lysimeter?

• A lysimeter is an instrument or installation designed to measure actual evapotranspiration. Examples: The Coshocton, Ohio, and San Dimas, California lysimeters.

  It is difficult to biult a properly functioning lysimeter because the model's boundary conditions cannot emulate the true boundary conditions in nature, leading to lysimeter spatial gradients that do not correspond with reality.

g. What is baseflow? Where does it comes from?

• Baseflow is the dry-weather flow of rivers. It originates in groundwater exfiltration.

h. To what five factors is to be attributed the recurrence of debris flows in the San Gabriel Mountains of Northeast Los Angeles? State them in causal order.

1. The uplift (through tectonism) of the mountain range (reported to be the highest in the U.S.).

2. The type of vegetative ecosystem (mediterranean, chaparral), which has developed adaptations to survive through droughts, including waxed leaf surfaces to minimize evapotranspiration. The mediterranean ecosystem occurs in midlatitudes (30^o-35^o) that have exposure to westerlies (trade winds from the west).

3. The wind storms (Santa Ana), which affects the region.

4. The wildland fires, propelled by drought and wind, which recur approximately every thirty years in chaparral ecosystems. The fires vaporize the waxy substances (in the litter and standing biomass) at the surface, and condense 1-5 cm inside the soil, creating the hydrophobic soil layer.

5. The intense rainfall events, exceeding 1 in/hr, which follow the fire because of enhanced coalescence in the lower atmosphere due to ash particles produced by the fire.