Abstract
We present the results of fog water collection obtained with cylindrical fog gauges at three locations on the northern side of Tenerife island (Spain): La Esperanza (1093 m a.s.l.), Taborno (1015 m a.s.l.), and El Gaitero (1747 m a.s.l.). Concomitant meteorological variables were also measured. We show that fog precipitation was more frequent than rainfall. However, the volumes and frequency of daily fog water collection varied among the three studied sites, usually not exceeding 10–40 L d−1/m2 of collecting surface. In La Esperanza, fog water harvesting occurred frequently, but was considerably lower than in the other two locations. However, while in Taborno fog water collection episodes were distributed throughout the period, in El Gaitero these were mainly concentrated in two periods, during autumn and winter 2012–2013. The study of the relationships between daily fog water yields and the averages of meteorological variables did not show any clear trend, but it suggested that the greater volumes of collected fog water were logically associated with higher wind speeds and lower solar radiation conditions. Fog water collection in La Esperanza and in Taborno typically occurred within a similar temperature interval (7.5–12.5 °C), while in El Gaitero the phenomenon was associated with a lower temperature range (2.5–10 °C).
Highlights
The vertical thermic structure of the atmosphere in the Macaronesian region is characterized by an increase in temperature with height
More recent studies using regular radiosonde data have confirmed these findings [3,4]. This leads to the presence of frequent low clouds or fog mainly on the northern slopes of the western Canary Islands. Despite these foggy conditions prevailing in the Canarian cloud forests, it is not yet clear whether horizontal precipitation represents a significant water input [5], or by contrast the role of fog is to reduce the vegetation water losses by evapotranspiration [6,7]
According to the number of recorded events, fog water collection proved to be more frequent than rainfall at the three monitoring sites
Summary
The vertical thermic structure of the atmosphere in the Macaronesian region is characterized by an increase in temperature with height This results from the atmospheric subsidence associated with the descending branch of the general circulation northern Hadley cell [1]. More recent studies using regular radiosonde data have confirmed these findings [3,4] This leads to the presence of frequent low clouds or fog mainly on the northern slopes of the western Canary Islands. Unlike the dew phenomenon, which implies water vapor condensation, fog water capture does not involve water phase changes This basically consists in collecting, mainly by impaction, the water droplets (0.1–200 μm in diameter; typically 50 μm; [12,13]) that travel suspended in a mass of water vapor saturated air. Liquid water content determines the potential (maximum) volume of water that can be obtained from the fog
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