CHAPTER 2 • The Maracaibo System: A Physical Profile
21
The geomorphology of the Maracaibo basin determines a distinctive synoptic climatology for the whole basin. The trade winds which predominate during the dry
season drive the air masses through the north-facing aperture of the basin and force
them first in a south-westerly direction over the Sierra de Perija and then in a southeasterly direction. At the same time the local winds over the lake cause a low pressure
area with its center over the mouth of the Catatumbo River, as already mentioned, and
creates a closed circulation pattern up to 2000 m altitude. The air forced over the Sierra de Perija originate, by convection, clouds of great vertical development which
produce frequent rains between 500 and 1500 m altitude. The low pressure over the
lake produces subsidence of the upper air and a scarcity of rain over the lake but at
the same time it forces down-valley currents of cold dry air from the Andes, creating
a convergence over the southern area of the lake (GOI1963). This convergence originates heavy rains through the whole year and is responsible for the large output of
the Catatumbo and other rivers of the south-western coast of the lake.
2.4.4
Water Balance
The large input of fresh water from the rivers, together with more modest volumes of
water from the direct precipitation over the lake, varies on a daily basis according to
the seasons. The deficiencies are compensated by the influx of sea water with the tides,
density currents and other phenomena. The first approximate water balance of the
basin was performed by Carter (1955). He calculated gains of 54.1 x 10 9 m3 yc' and
losses of 54.4 x 10 9 m 3 yc'. On a monthly basis he obtained negative values for February and March, compensated by an influx of sea water from the Gulf of Venezuela to
the lake.
A more detailed analysis was performed by Corona (1964) using the equation
s= Ve+V,-E"
where Ve is river runoff; V, is precipitation over the lake and E, is evaporation from the
lake. He obtained the the annual balance presented in Table 2.1 , including Tablazo Bay.
In this analysis all the monthly values are positive. The discharge from the mouth
of the estuary according to these results varies between 492 and 2695 m3 s-'. Based on
Carter (1955) analysis and on a balance of the Deuterium content in the waters, Friedman et al. (1956) deduced a residence time of 6 years and 10 months for the water in
the lake. Recently the residence time has been more accurately calculated in 5.99 years
based on precipitation data from 1958-1977 (Escam 1991).
Table 2.1. Annual balance
(x 109 m3 yr-') of the basin
Gains
Runoff (Ve)
51.1
Precipitation (Vl)
15.1
Total
66.2
To the sea (5)
Evaporation (El )
Losses
49.1
17.1
66.2
21
The geomorphology of the Maracaibo basin determines a distinctive synoptic climatology for the whole basin. The trade winds which predominate during the dry
season drive the air masses through the north-facing aperture of the basin and force
them first in a south-westerly direction over the Sierra de Perija and then in a southeasterly direction. At the same time the local winds over the lake cause a low pressure
area with its center over the mouth of the Catatumbo River, as already mentioned, and
creates a closed circulation pattern up to 2000 m altitude. The air forced over the Sierra de Perija originate, by convection, clouds of great vertical development which
produce frequent rains between 500 and 1500 m altitude. The low pressure over the
lake produces subsidence of the upper air and a scarcity of rain over the lake but at
the same time it forces down-valley currents of cold dry air from the Andes, creating
a convergence over the southern area of the lake (GOI1963). This convergence originates heavy rains through the whole year and is responsible for the large output of
the Catatumbo and other rivers of the south-western coast of the lake.
2.4.4
Water Balance
The large input of fresh water from the rivers, together with more modest volumes of
water from the direct precipitation over the lake, varies on a daily basis according to
the seasons. The deficiencies are compensated by the influx of sea water with the tides,
density currents and other phenomena. The first approximate water balance of the
basin was performed by Carter (1955). He calculated gains of 54.1 x 10 9 m3 yc' and
losses of 54.4 x 10 9 m 3 yc'. On a monthly basis he obtained negative values for February and March, compensated by an influx of sea water from the Gulf of Venezuela to
the lake.
A more detailed analysis was performed by Corona (1964) using the equation
s= Ve+V,-E"
where Ve is river runoff; V, is precipitation over the lake and E, is evaporation from the
lake. He obtained the the annual balance presented in Table 2.1 , including Tablazo Bay.
In this analysis all the monthly values are positive. The discharge from the mouth
of the estuary according to these results varies between 492 and 2695 m3 s-'. Based on
Carter (1955) analysis and on a balance of the Deuterium content in the waters, Friedman et al. (1956) deduced a residence time of 6 years and 10 months for the water in
the lake. Recently the residence time has been more accurately calculated in 5.99 years
based on precipitation data from 1958-1977 (Escam 1991).
Table 2.1. Annual balance
(x 109 m3 yr-') of the basin
Gains
Runoff (Ve)
51.1
Precipitation (Vl)
15.1
Total
66.2
To the sea (5)
Evaporation (El )
Losses
49.1
17.1
66.2