Figure 2.5. (left) Mean monthly temperature (°C) at 1460 m at Monteverde (•; mean ± mean monthly minimum and
maximum values), Limon (•), Ciudad Quesada (•), Irazu (+), San Jose (A), and Puntarenas (V). See Table 2.1 for site
descriptions. Figure 2.6. (right) Mean monthly precipitation depth (mm) at 1460 m at Monteverde (•; mean ± 1
S.D.), Limon (•), Ciudad Quesada (•), Irazu (+), San Jose (A), and Puntarenas (T). See Table 2.1 for site descriptions.The migration of the ITCZ controls the seasonally of
precipitation and the types of clouds and precipi-
tation, particularly on upper slopes and ridges in
Monteverde. In areas that are exposed to the trade
winds, moisture from clouds and wind-driven pre-
cipitation intercepted by the vegetation may represent
a major hydrological input; the actual contribution
to a forest is difficult to quantify (Stadtmuller 1987,
Cavelier and Goldstein 1989, Bruijnzeel and Proctor
1993, Cavelier et al. 1996). Terms for cloud water and
mist inputs include "occult precipitation" (Bollard et
al. 1983), and "horizontal precipitation" (sensu Stadt-
muller 1987, Bruijnzeel and Proctor 1993) when wind-
driven precipitation is included. We define "con-
vective precipitation" as precipitation that originates
from cumulus or cumulonimbus clouds (mean wind-
speeds < 2 m/s), "wind-driven precipitation" as pre-
cipitation that originates from stratus or stratocumu-
lus clouds with minimal cloud immersion (mean
windspeeds > 2 m/s), "mist" as precipitation that
originates from stratus clouds with cloud immersion,
and "cloud water" as nonprecipitating stratus cloud
immersion.
Three seasons are recognized in Monteverde on the
basis of cloud and precipitation types: (1) wet season
(May-October), characterized by clear sky in the
morning and cumulus cloud formation and convec-
tive precipitation in the afternoon and early evening;
(2) transition season (November-January), character-
ized by strong northeasterly trade winds, stratus and
stratocumulus clouds, and wind-driven precipitation
and mist during the day and night; and (3) dry sea-
son (February-April), characterized by moderate
trade winds, stratus clouds or clear-sky conditions,
and wind-driven mist and cloud water, particularly
during the night (Fig. 2.6). During the transition and
dry seasons, stratus cloud cover and wind-driven pre-
cipitation, mist, and cloud water depths typically in-
crease with elevation and exposure to the trade winds.
Maximum monthly precipitation in Monteverde
occurs in the wet season in June, September, and
October, when the ITCZ is directly over Costa Rica
(Fig. 2.6). This occurs during maximum solar heating
of land and sea surfaces, which results in high rates
of heat (sensible heat) and water vapor release (latent
heat) to the atmosphere (referred to as sensible and
latent heat exchange, respectively). Absorbance of sen-
sible heat by the atmosphere produces warm, buoyant
air masses and generally unstable atmospheric condi-
tions. Adiabatic cooling of these moist, ascending air
masses causes water vapor to condense and leads to
the formation of cumulus and cumulonimbus clouds
by the late morning and early afternoon. Cloud height
may reach over 15,000 m. Clouds typically produce
convective precipitation by the afternoon or early
evening, often associated with intense lightning ac-
tivity. When the ITCZ is at its northern boundary in
late July and August, convective precipitation activ-
ity is typically reduced in Monteverde, a period re-
ferred to as the "veranillo" (little summer); light to
moderate winds with mist and precipitation are in-
terspersed with periods of convective precipitation.18 The Physical Environment