Quantification of cloud water interception along the windward slope of Santa Cruz Island, Galapagos (Ecuador)

Abstract

International audienceThe Galapagos Archipelago is nearly devoid of freshwater resources, but during six months of the year, a fog layer covers the windward slopes of the main islands. In order to investigate the hydrological importance of this phenomenon, a monitoring network was set up on Santa Cruz Island, at the center of the archipelago. Meteorological parameters were monitored together with throughfall and stemflow at two stations: a first in a secondary forest at the lowest fringe of the fog layer (400 m a.s.l.), and a second in shrub lands of the Galapagos National Park, at the center of the fog layer (650 m a.s.l.). Cloud water interception was quantified from the wet canopy water budget, based on a modified \emph{Rutter}-type canopy interception model. This methodology allowed the estimation of fog interception for short time intervals (15 min) and avoided the subjective separation into individual rainfall events. Fog was found to be a negligible water input at the lower site, but contributed up to 26 $\pm$ 16\% of incident rainfall at the higher site. Wind was shown to enhance fog interception, but this alone could not explain the difference in fog catch between the two sites. Higher liquid water content and more frequent fog occurrence contributed to the difference as well. This study highlights that the presence of fog may induce a marked increase of net precipitation, but this effect is restricted to the summit areas exposed to winds, located in the center of the cloud belt

Hydrogeological settings of a volcanic island (San Cristóbal, Galapagos) from joint interpretation of airborne electromagnetics and geomorphological observations

“…415 mm yr −1 per 100 m elevation from the coast up to the elevation of 440 m a.s.l. (d 'Ozouville, 2007b;Pryet et al, 2012). On the basis of these values, the median annual total along the windward side of San Cristóbal is estimated to 1580 mm .…”

El Niño evolution during the Holocene revealed by a biomarker rain gauge in the Galápagos Islands

“…Lowelevation clouds prevent the lake from desiccation during the winter time, and a light drizzle, known locally as garúa, may contribute up to 25% of the water to the lake catchment annually (Pryet et al, 2012). As the lake is filled by rain falling within the narrow crater rim, its depth fluctuates slightly with the seasons.…”

Galápagos hydroclimate of the Common Era from paired microalgal and mangrove biomarker 2 H/ 1 H values

“…At the 670-m elevation of El Junco Lake, for reasons that are not well understood, Galápagos highlands receive the majority of annual precipitation as frequent light rains in the cool season when the ITCZ is furthest north and the lowlands remain dry (23). Highland sites also receive 26 ± 16% of cool season rainfall from direct cloud water interception associated with garua fog (30). Changes to the intensity and or distribution of either of these moisture sources may have altered the hydrologic balance of El Junco in ways that did not manifest equally in the sand and biomarker isotope records and may have caused an earlier onset of wetter conditions (Fig.…”