What is deep percolation in the context of L'vovich's water balance? What is its value as a fraction of precipitation? Why? Explain the physical basis for this behavior.

Deep percolation is the fraction of precipitation that reaches the groundwater but does not return eventually to the surface waters as baseflow. Its global value is less than 5%, with an average of less than 2%. The value is a small fraction of precipitation because the predominant direction of groundwater follows a nearly horizontal gradient, toward the local/regional exit as baseflow.

Contrast the contributions of Dalton, Penman, Monteith and Shuttleworth-Wallace in evaporation modeling. Use a tabular form for the comparison.

Dalton	Penman	Monteith	Shuttleworth-Wallace
Mass-transfer method only	Combination method (mass transfer and energy balance)	Physically-based combination method, featuring two resistances, external and internal	Physically-based combination method, featuring five resistances, accounting for plant canopy evaporation and the soil or water in which they are growing.

Explain the controversy regarding how to account for initial abstraction in the runoff curve number method, as interpreted by hydrologic models in current use, such as HEC-HMS and EPA SWMM. How did Mockus propose to solve the problem of quantifying the initial abstraction?

Mockus proposed to plot runoff vs effective precipitation, but was overruled by his superiors. They zeroed on the initial abstraction as a constant fraction of precipitation, with the constant set at λ = 0.2 from the beginning (1954). Initially, the runoff curve number method was intended to be lumped in time. i.e., for precipitation not to vary within the storm duration. However, in practice, users have specified the initial abstraction as varying within the storm duration, effectively rendering it distributed. Currently, there is no standard on how to temporally account for initial abstraction.

Why is the Mockus approach to runoff generation, for the most part, better than Horton's for practical applications? Explain.

Why is the time of concentration calculated by the kinematic wave model likely to be much less than that calculated with a storage concept or diffusion wave? Explain the physical (mechanical) reason for this behavior.

(a) What is the mean albedo of the Earth's surface? (b) Has it changed from ancient times to the present time? How much, according to published studies? (c) How does albedo vary from rain forests to deserts? (d) Is it possible for humans to change the albedo of the ground surface? How?

Discuss the apparent reason for the persistence of the Sahel drought of 1970-85. What is the perceived role of transhumance (or the lack of it) in the Sahel drought?

Why is the diffusion wave model of catchment dynamics likely to be more accurate that the kinematic wave models of HEC-HMS and Li? What is the reason for their different numerical behavior?

What is the Walker cell? What is the root cause of the El Niño phenomenon? How often does an El Niño event likely to recur? What are the effects of an El Niño event?

How much is the mean annual global terrestrial precipitation, in mm? How was this value obtained (calculated)? For what part of the climatic spectrum of precipitation are droughts likely to be more persistent? Why? Give an example.