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The Cloudbridge
Nature Reserve - Research Reports
Rainfall and Temperature
Ian Giddy
Background Cloudbridge is on the Pacific side of the Talamanca mountain range. The climate of the Pacific is marked by the presence of a "dry" season that lasts for four months (and more in some zones). At Cloudbridge, there is no pure dry season -- it rains, at least for an hour or two, almost every day. The reason lies in the height of the Talamanca mountains. Further north, the warm moist air driven westward by the trade winds loses its moisture as it crosses the cordilleras and the resulting dry air gusts down the Pacific slopes drying out everything in its path. With such low moisture content, few clouds form to block the sunshine and the prevailing winds keep Pacific breezes from bringing moisture onshore, thus further promoting the dryness. The southern half of the Pacific slope is not
normally as strongly influenced by these effects because
the lofty Talamanca range blocks the drying winds to
some degree. This allows moist air to be brought in from the Pacific
Ocean. Air is forced up the mountainside, and as it cools it forms
mist, clouds or rain, even in the dry season. The cloud forest is
caused by air passing over hilly terrain and condensing its moisture on
the leaves of plants and trees.
The rainy period is interrupted by "veranillos," or little summers. The veranillos last for one to two weeks, almost always in July, when precipitation decreases considerably in all the Pacific Zone. When one occurs early (end of June), its known popularly as "Veranillo de San Juan." If it occurs in July or the beginning of August, sometimes with alternating dry and rainy days, people refer to it as the canicula. The following charts represent 3 years of daily tracking rainfall and temperatures at Casa Amanzimtoti
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Copyright
©2006 Ian Giddy. All rights reserved. Last revised 24 March 2006
At Cloudbridge, rain falls almost
every day, usually starting
in the early afternoon. This is common in the tropics. The sun warms
the ground during the day. By afternoon the
moist, unstable air is being forced to rise giving rise initially to
clouds and then to heavy rain that arrives rapidly.
