24
Climatic Geomorphology
(a) First-order morphogenetic regions, considered as non-seasonal by Beckinsale and
Chorley (1991), comprising the glacial, arid and humid tropical regions. These are
characterized by the occurrence of non-seasonal processes with low erosion rates,
except those related to sporadic events such as surging glaciers, desert storms and
mass movements. The central zones of these non-seasonal regions persist latitudinally
during climatic changes.
(b) Second-order morphogenetic regions, considered as seasonal ones by the same
authors, comprising tropical wet-dry, semiarid, dry continental, humid mid-latitude
and periglacial regions. These have seasonal processes, occasionally of high intensity
accompanying important changes. In these regions it is possible to differentiate
warmer climates (tropical wet-dry and semiarid) where geomorphic processes differ
significantly in terms of length of the wet season; and cooler climates (dry continental,
humid mid-latitude and periglacial) whose geomorphic processes differ mainly in
respect of summer temperatures and also partly with the precipitation amounts. These
authors detail a map modifying that elaborated by Tricart and Cailleux (1965) of the
current distribution of these eight morphogenetic regional types.
Data usually managed in geomorphology are those directly provided by climatology,
such as those used by Peltier (1950), Tanner (1961), Leopold et al. (1964), Wilson (1968,
1969), Chorley et al. (1984), and others. These data can be reasonably adequate to develop
broad overviews about geomorphic processes. Whatever the case, the utilized mean
numeric values are inadequate because most of the quoted surface processes have a
discontinuous nature with relevant variations in frequency and magnitude (Ahnert, 1987b,
1996; De Ploey et al., 1991). Therefore, it seems to be necessary to use other kinds of
numerical parameters such as rainfall intensity, wind velocity, frequency and duration
of freeze and so forth. Once these numerical data have been selected, a frequencymagnitude analysis can be performed to characterize the morphoclimatic elements. Ahnert
(1987b) proposed a magnitude-frequency index for precipitation from which can be
recognized the distribution of meteorological events of geomorphologic meaning.
De Ploey et al. (1991), using daily precipitation values, obtained a sort of quantification
of the accumulative potential erosion, which may serve to evaluate slope erosion by
laminar overland flows. This kind of approach is not only useful for the characterization of
morphoclimates but also can be applied to other branches of the science (Ahnert, 1987b).
This method cannot identify non-episodic climatic features such as seasonality; however,
it is a first step towards a more comprehensive morphoclimatology.
There is a general agreement about the concept and focus of climatic geomorphology,
but also some criticisms and objections have been made by some authors. Stoddart
(1969a) considered that is not realistic to take into account only a particular set of
factors, because clear misrepresentations may arise. Climatic factors are, of course,
important, but not the dominant ones; landscape builds from complex interactions among
climate, bedrock lithology and vegetation, and it is not possible to separate climatic
geomorphology from other geomorphologic approaches. Baker and Twidale (1991)
indicated that only the glacial and arid morphogenetic regions can be easily identified,
whereas the other climatic landscapes can hardly be recognized and defined. Twidale and
Lageat (1994) pointed out that the glacial, periglacial and arid morphoclimatic regions
represent 50 per cent of the Earth surface, and the other half is occupied by humid zones
Climatic Geomorphology
(a) First-order morphogenetic regions, considered as non-seasonal by Beckinsale and
Chorley (1991), comprising the glacial, arid and humid tropical regions. These are
characterized by the occurrence of non-seasonal processes with low erosion rates,
except those related to sporadic events such as surging glaciers, desert storms and
mass movements. The central zones of these non-seasonal regions persist latitudinally
during climatic changes.
(b) Second-order morphogenetic regions, considered as seasonal ones by the same
authors, comprising tropical wet-dry, semiarid, dry continental, humid mid-latitude
and periglacial regions. These have seasonal processes, occasionally of high intensity
accompanying important changes. In these regions it is possible to differentiate
warmer climates (tropical wet-dry and semiarid) where geomorphic processes differ
significantly in terms of length of the wet season; and cooler climates (dry continental,
humid mid-latitude and periglacial) whose geomorphic processes differ mainly in
respect of summer temperatures and also partly with the precipitation amounts. These
authors detail a map modifying that elaborated by Tricart and Cailleux (1965) of the
current distribution of these eight morphogenetic regional types.
Data usually managed in geomorphology are those directly provided by climatology,
such as those used by Peltier (1950), Tanner (1961), Leopold et al. (1964), Wilson (1968,
1969), Chorley et al. (1984), and others. These data can be reasonably adequate to develop
broad overviews about geomorphic processes. Whatever the case, the utilized mean
numeric values are inadequate because most of the quoted surface processes have a
discontinuous nature with relevant variations in frequency and magnitude (Ahnert, 1987b,
1996; De Ploey et al., 1991). Therefore, it seems to be necessary to use other kinds of
numerical parameters such as rainfall intensity, wind velocity, frequency and duration
of freeze and so forth. Once these numerical data have been selected, a frequencymagnitude analysis can be performed to characterize the morphoclimatic elements. Ahnert
(1987b) proposed a magnitude-frequency index for precipitation from which can be
recognized the distribution of meteorological events of geomorphologic meaning.
De Ploey et al. (1991), using daily precipitation values, obtained a sort of quantification
of the accumulative potential erosion, which may serve to evaluate slope erosion by
laminar overland flows. This kind of approach is not only useful for the characterization of
morphoclimates but also can be applied to other branches of the science (Ahnert, 1987b).
This method cannot identify non-episodic climatic features such as seasonality; however,
it is a first step towards a more comprehensive morphoclimatology.
There is a general agreement about the concept and focus of climatic geomorphology,
but also some criticisms and objections have been made by some authors. Stoddart
(1969a) considered that is not realistic to take into account only a particular set of
factors, because clear misrepresentations may arise. Climatic factors are, of course,
important, but not the dominant ones; landscape builds from complex interactions among
climate, bedrock lithology and vegetation, and it is not possible to separate climatic
geomorphology from other geomorphologic approaches. Baker and Twidale (1991)
indicated that only the glacial and arid morphogenetic regions can be easily identified,
whereas the other climatic landscapes can hardly be recognized and defined. Twidale and
Lageat (1994) pointed out that the glacial, periglacial and arid morphoclimatic regions
represent 50 per cent of the Earth surface, and the other half is occupied by humid zones