Geoscience Reference
In-Depth Information
Figure A1.1
Characteristic annual
energy balances for ten different climatic
types (Köppen symbols and Strahler
classification numbers shown). The
ordinate shows energy flux density
normalized with the maximum monthly
net all-wavelength radiation (
R
n
) normal-
ized with the maximum monthly value
as unity. The abscissa intervals indicate
the months of the year with summer in
the centre.
H
= turbulent flux of sen-
sible heat and
LE
= turbulent latent heat
flux to the atmosphere.
Source
: From Kraus and Alkhalaf (1995),
copyright © John Wiley & Sons Ltd.
Reproduced with permission.
A novel feature of the system is that the thermal effi-
ciency is derived from the PE value, which itself is
a function of temperature. The climate types defined
by these two factors are shown in Table A1.1; both
elements are subdivided according to the season of
moisture deficit or surplus and the seasonal concen-
tration of thermal efficiency.
The system has been applied to many regions, but
no world map has been published. Unlike the Köppen
approach, vegetation boundaries are not used to
determine climatic ones. In eastern North America,
vegetation boundaries do coincide reasonably closely
with patterns of
PE
, but in tropical and semi-arid areas
the method is less satisfactory.
M. I. Budyko developed a more fundamental
approach using net radiation instead of temperature (see
Chapter 4C). He related the net radiation available for
evaporation from a wet surface (
R
o
) to the heat required
to evaporate the mean annual precipitation (
L
r). This
ratio
R
o
/
L
r (where
L
= latent heat of evaporation) is
