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Climatic Geomorphology
This indicates that in the past these dry zones underwent conditions much more humid
than at present. Hence, the recognition of processes and deposits in the humid tropics helps
in the interpretation of climatic variations in past times.
2. Climatic characteristics, vegetation and morphoclimatic domains
Climatic parameters play an essential role in the dynamics and intensity of geomorphological processes, as well as in the nature of the resulting landforms (Faniran and Jeje,
1983). For this reason, it is convenient to know the magnitude of these parameters and
their variability.
Temperatures in the humid tropics are moderate and do not exceed 34~ very different
from the tropical deserts, with values higher than 50~ Mean annual temperatures
fluctuate between 24 and 30~ measured at sea level. Seasonal and annual variations are
lower than 2~ This thermal uniformity is broken with increased altitude, which is
accompanied by cloud intensification.
In the humid tropics humidity is always high. Relative humidity often exceeds 80%,
and normal values throughout the year do not move far from this number. Maximum
potential evapotranspiration is recorded in the equatorial zones and varies between 1000
and 1500 mm/yr.
With the exception of very elevated areas, precipitation is in the form of rain. As
temperature is quite uniform, seasonality is marked by precipitation variability.
Thunderstorms are very common, and contribute some 90% to the total rainfall in
savanna zones. Most thunderstorms start in the afternoon and have short duration. The
strongest one ever recorded produced an 1870 mm rainfall in a single day, 16 March 1952,
in Cilaos on Reunion Island. In the humid tropics 40% of the precipitation has an intensity
higher than 25 mm/h and several records are known with intensities of up to 340 mm/h
for some minutes (Reading et al., 1995). Precipitation regimes are as follows (Birot, 1973):
(1) Tropical areas of equatorial regions influenced by the Intertropical Convergence
Zone, rainfall through all the year and one single maximum. Annual average precipitation
is about 2000 mm or much higher. (2) Areas within 10 ~ latitude north and south of the
Equator, with two dry and two rainy seasons and precipitation ranging between 1000 and
2000 mm. In this humid and dry tropical regime rainy seasons can be shorter and
precipitation can reach 650 to 1000 mm. (3) Dry regime, with precipitation between 250
and 650 mm, located on the desert margins.
Vegetation in the humid tropics is a direct response to the existing climatic regime.
An equatorial rain forest (pluvisilva) can be differentiated, which is constituted by very
close trees of up to 40 m high with large perennial leaves and thousands of tree species
(Figure 20.1). The high vegetation density generates a continuous shadow on the ground.
Coastal vegetation is represented by mangroves. The rainforest mainly develops in the
Amazon and Congo basins, Central America and SE Asia and Indonesia. The savanna is a
consequence of a humid-dry tropical climatic regime. It is formed by very isolated trees,
sometimes grouped in corridors following valley bottoms, that arise upon a grassland
of tall graminoids, commonly higher than a person (Figure 20.2). Summer fires in these
yellow dry graminoids are very frequent and are responsible for the grassland predominance over the forest. The savanna is mainly located in central and southern Africa,
Climatic Geomorphology
This indicates that in the past these dry zones underwent conditions much more humid
than at present. Hence, the recognition of processes and deposits in the humid tropics helps
in the interpretation of climatic variations in past times.
2. Climatic characteristics, vegetation and morphoclimatic domains
Climatic parameters play an essential role in the dynamics and intensity of geomorphological processes, as well as in the nature of the resulting landforms (Faniran and Jeje,
1983). For this reason, it is convenient to know the magnitude of these parameters and
their variability.
Temperatures in the humid tropics are moderate and do not exceed 34~ very different
from the tropical deserts, with values higher than 50~ Mean annual temperatures
fluctuate between 24 and 30~ measured at sea level. Seasonal and annual variations are
lower than 2~ This thermal uniformity is broken with increased altitude, which is
accompanied by cloud intensification.
In the humid tropics humidity is always high. Relative humidity often exceeds 80%,
and normal values throughout the year do not move far from this number. Maximum
potential evapotranspiration is recorded in the equatorial zones and varies between 1000
and 1500 mm/yr.
With the exception of very elevated areas, precipitation is in the form of rain. As
temperature is quite uniform, seasonality is marked by precipitation variability.
Thunderstorms are very common, and contribute some 90% to the total rainfall in
savanna zones. Most thunderstorms start in the afternoon and have short duration. The
strongest one ever recorded produced an 1870 mm rainfall in a single day, 16 March 1952,
in Cilaos on Reunion Island. In the humid tropics 40% of the precipitation has an intensity
higher than 25 mm/h and several records are known with intensities of up to 340 mm/h
for some minutes (Reading et al., 1995). Precipitation regimes are as follows (Birot, 1973):
(1) Tropical areas of equatorial regions influenced by the Intertropical Convergence
Zone, rainfall through all the year and one single maximum. Annual average precipitation
is about 2000 mm or much higher. (2) Areas within 10 ~ latitude north and south of the
Equator, with two dry and two rainy seasons and precipitation ranging between 1000 and
2000 mm. In this humid and dry tropical regime rainy seasons can be shorter and
precipitation can reach 650 to 1000 mm. (3) Dry regime, with precipitation between 250
and 650 mm, located on the desert margins.
Vegetation in the humid tropics is a direct response to the existing climatic regime.
An equatorial rain forest (pluvisilva) can be differentiated, which is constituted by very
close trees of up to 40 m high with large perennial leaves and thousands of tree species
(Figure 20.1). The high vegetation density generates a continuous shadow on the ground.
Coastal vegetation is represented by mangroves. The rainforest mainly develops in the
Amazon and Congo basins, Central America and SE Asia and Indonesia. The savanna is a
consequence of a humid-dry tropical climatic regime. It is formed by very isolated trees,
sometimes grouped in corridors following valley bottoms, that arise upon a grassland
of tall graminoids, commonly higher than a person (Figure 20.2). Summer fires in these
yellow dry graminoids are very frequent and are responsible for the grassland predominance over the forest. The savanna is mainly located in central and southern Africa,