Introduction
Ecuador straddles the equator. Its day length, then, varies little through the year. Its climate, however, is much more complex than might be expected. This
complexity arises from the interaction between the prevailing winds, the Andes, and the pacific ocean currents.
Overall, these interactions lead to two regional climatic gradients. The temperature decreases with altitide, ranging from Tropical to Arctic. Rainfall, likewise,
ranges from practically nill in the southwest to as wet as possible. Furthermore, the seasonality of the rainfall varies considerably across the country, becoming
less pronounced the farther from the coast one gets.
That the climatic gradients do not coincide is one of the main reasons why there are few places in the world with so diverse an ecology as Ecuador.
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The Equatorial Trade Winds
The Andes
Pacific Ocean currents
The trade winds, originating over the Atlantic Ocean converge
over South America from the northeast and southeast, depositing
the moisture they have collected from the tropical Atlantic in
two main bands: the coastal mountains of northeast Brazil and
the Andes.
Before continental drift resulted in the rise of the Andes, the
rivers of S. America flowed east to west. Amazonian valleys, therefore,
are much broader near their source than they are near the sea
and are very sluggish and prone to massive flooding. Water is
thereby retained in the heart of the continent, allowing it to
be used
to feed the rainforest.
The water contained within the Amazon Basin is not, of itself,
capable of sustaining the ecosystem. The Rainforest does that
itself. The trees pump water back into the atmosphere far more
efficiently than evaporation of groundwater could. This saturates
the air and leads to local storms, dispersing water which otherwise
would collect uselessly in the river system, and spreading the
rain over time, making the Amazon less vulnerable to seasonal
fluctuations in the trade winds.
depleted land is then left for the forest to reclaim. This is a sustainable method only when practised on the small scale. If too much forest is destroyed, there can be no recovery, because there are no nutrients to fuel it. A degraded rainforest is one step from being a very wet desert.
The Atlantic trade winds, hitting the Andes are forced high in the atmosphere, depositing their moisture as rain on the eastern slopes. Were the Andes lower, this would probably lead to a rain shadow west of the mountains. Instead the low pressure caused by the uplift draws air in from over the Pacific Ocean.
In the south of the country, the Pacific is cold and the indrawn air dry. This results in arid conditions. Seasonal fluctuations in the ocean currents, however, result in marked wet and dry seasons, giving rise to deciduous tropical forests. In the north, by contrast, the Pacific is warm and the air wet. This gives rise to a second
belt of rain over the coastal highlands. The Bilsa forest, of which the Yorkshire Rainforest Reserve is a part, is in these mountains.
The Andes divide Ecuador into three distinct zones. In the east, the weather is uniformly hot and wet and results in typical Amazonian Rainforest. In the mountains, the temperature declines with height, resulting in a gradual change from tropical to alpine and even arctic vegetation. In the west, the weather is dominated by the effects of two converging ocean currents. A cold north flowing current and a warm southerly one create a rainfall gradient along the coast, and
one which shows seasonal variations. The flora as a result is exceptionally diverse.
Bellamy?s book, "Botanic Man" (Hamlyn 1978).
Without moving far from the Equator, it is possible, within a few tens of miles, to pass through vegetation typical of all the world?s latitudes.
The Peru Current and El Nino Events
The dominant oceanic current in the South Pacific flows counter-clockwise from the Antarctic, along the coast, turning west off the southern coast of Ecuador. This cold water gives rise to desert conditions along the Chile-Peru coast. A warm counter-current flows in the north, but this is much weaker because it flows counter to the prevailing winds, but it gives enough water to support rainforests from Ecuador northwards. When the Peru current fails, as it frequently does, the climate of the region changes dramatically. Around December the trade winds over the Pacific fail and the
Pacific coast of South America enters its rainy season. Because of this timing, the westerly winds which result are called "El Niño" (the boy child) after Christ.
Throughout the year, the prevailing easterly trade winds have
driven water into the western Pacific, creating a hill of water
which is heated by an equatorial sun. When the trades fail, this
water flows back, overlaying the cold Peruvian current and bringing
torrential rain to the previously dry Pacific coast of South America.
El Niño events are very irregular, both in strength and duration.
They bring rain to an otherwise arid region but they can also
bring destruction. In some years theocean surface can warm by
almost 7K and rise by 20cm. The anchovy fisheries which depend
on the cold Peruvian waters are destroyed, as is the guano industry,
which depends on the seabirds which feed on the anchovy. The 1994
El Niño event was very strong. It prevented loggers from entering
the Bilsa forest
throughout 1995, thus enabling Fundación Jatun Sacha to establish
a Biological Station of which the Yorkshire Rainforest Reserve
is a part.
