Abstract
The Galapagos Archipelago is a semiarid zone scarce of superficial water resources. Due to its geographic location and the presence of oceanic currents, these islands are covered by fog during seven months along the year which could represent a potential source of water supply. In this study, the feasibility of fog collection for domestic rural use and irrigation was investigated using two Standard Fog Collectors (SFC) of 50% and 35% shade coefficient of 1 m2 and a cylindrical fog net (CFN) of 0.15 m2 at 600 m of elevation in the windward side of San Cristobal Island (Galapagos). The methodology applied consists in the quantification of the monthly and annual water balance at different altitudes in an average and dry years, using the orographic gradients of rainfall, evapotranspiration and cloud water interception. The latter was used to estimate the fog water availability to satisfy any water deficit. Fog water interception was estimated using a geometric model and the use of different climatic variables. On the other hand, water demand in the rural zone for domestic consumption and livestock was estimated with the quota method, and the water demand for agriculture was estimated through the water balance. Results show that the amount of fog captured reaches 7.9, 5.9 and 3.4 mm/d with 50-SFC, 35-SFC and CFN, respectively. Comparing these results with other locations in the world, fog water collection in Galapagos is above the average. A fog gauge system of 50-SFC was designed at different elevations to cover the 25% and 15% of the water deficit in the average and dry year, respectively.
Highlights
The Galapagos Archipelago is a semi-arid zone where most of their islands suffer from the lack of superficial water resources, which limits the development of productive activities, and it affects the life quality of their inhabitants
Fog estimated at 50-Standard Fog Collectors (SFC), 35-SFC and cylindrical fog net (CFN) represents 490%, 394% and 229% of total rainfall, respectively, which is a considerable amount in a water balance
Even though CFN impaction efficiency is improved by the small holes of the mesh and its high shade coefficient, fog interception is reduced because the drops captured by the mesh can block the air flux, decreasing its permeability, so this air flux is not able to pass through but it could carry the drops that were already impregnated in the mesh with it, preventing this fog water to reach the gutter
Summary
The Galapagos Archipelago is a semi-arid zone where most of their islands suffer from the lack of superficial water resources, which limits the development of productive activities, and it affects the life quality of their inhabitants. It is necessary to find alternatives to enhance water supply in Galapagos, such as fog harvesting. These islands are covered by a semi-permanent fog layer in the windward side (above 250 m a.s.l.), from June to December. Such circumstances could be resourceful to consider fog as a potential source for water supply
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