Geoscience Reference
In-Depth Information
Tschinkel, H. M. (1963). Short-term fluctuation in streamflow as related to evaporation and
transpiration.
J. Geophys. Res.
,
68
, 6459-6469.
VanBavel, C. H. M. (1961). Lysimetric measurements of evapotranspiration rates in the eastern United
States.
Soil Sci. Soc. Amer. Proc.
,
25
, 138-141.
(1967). Changes in canopy resistance to water loss from alfalfa induced by soil water depletion.
Agr. Met.
,
4
, 165-176.
VanBavel, C. H. M. and Reginato, R. J. (1962). Precision lysimetry for direct measurement of
evaporative flux.
Intern. Sympos. Methodol. of Plant Eco-Physiol.
, Montpellier, France,
pp. 129-135.
Webb, E. K. (1964). Further note on evaporation with fluctuating Bowen ratio.
J. Geophys. Res.
,
69
,
2649-2650.
Wesely, M. (1988). Use of variance techniques to measure dry air-surface exchange rates.
Bound.-Layer Met.
,
44
, 13-31.
Wittenberg, H. and Sivapalan, M. (1999). Watershed groundwater balance estimation using streamflow
recession analysis and baseflow separation.
J. Hydrol.
,
219
, 20-33.
Yarosh, E. S., Ropelewsky, C. F. and Mitchell, K. E. (1996). Comparisons of humidity observations and
ETA model analyses and forecasts for water balance studies.
J. Geophys. Res.
,
101
(D18),
23 289-23 298.
PROBLEMS
4.1
Derive Equation (4.4) from (2.41) and (2.44).
The local vertical vapor flux over a large, uniform, grass surface is measured to be 4 mm d
−
1
.
At 2.0 m above the surface, the air temperature, the relative humidity and the wind speed are
20
◦
C, 60% and 5 m s
−
1
. Calculate the value of the wind speed and the specific humidity at 10 m,
assuming a neutral practically isothermal atmosphere and a surface roughness of 1 cm. Ignore the
displacement height.
4.2
Suppose you are given the local evaporation rate,
E
(inmmd
−
1
), from a wet surface at ground
level. The surface temperature and the surface specific humidity are
T
s
and
q
s
, respectively. The
corresponding values at2melevation are
T
2
for temperature and
q
2
for specific humidity. Derive
an expression for the local turbulent sensible heat flux,
H
(inWm
−
2
), near the ground in terms
of these variables. (Do not use Bowen's ratio or the psychrometric constant as a variable in your
final expression.)
4.3
4.4
Prove Equation (4.6).
4.5
Show a derivation of Equation (4.28) from (4.4), (4.6) and (4.7).
4.6
Multiple choice. Indicate which of the following statements are correct. The empirical mass-
transfer approach consists of determining
m
ean evaporation from a water surface by means of an
equation of the type of (4.7), inwhich
f
e
(
u
1
) is some known function of the mean wind speed at
agiven elevation.
(a)
For long-term (say1dorlonger) averages, the wind function, which appears in Equation
(4.7), is also needed to calculate the Bowen ratio.
(b)
Equation (4.7) is less useful over crop-covered land, because it requires the determination
of
q
s
at a surface, which is often irregular and ill defined.
