THE OCCURRENCE OF FOG IN CHILE

The topography in Chile is extremely complex and many types of fog are found; both factors complicate the presentation of the data. Despite this, measurements from standard meteorological stations suggest a latitudinal maximum in fog frequency between 35-degrees and 40-degrees-S for coastal stations. This is supported by data from inland stations in Chile and the available observations from Argentina on the Atlantic coast of South America. Along the Chilean coast the average number of days with fog ranges from 3 to 59 per year. The variation in fog frequencies is related to persistent synoptic-scale circulation patterns and to ocean currents.Specialized fog observations were made at three remote locations in northern Chile to determine fog frequencies on the coastal mountains. The sites were in a very arid region (26-degrees-28-degrees-S) near a large-scale fog-water collection project. Fog frequencies as high as 189 days per year with another 84 days of patchy fog were reported at an altitude of 860 m. These are 3-15 times higher than at low-elevation coastal locations at similar latitudes. Clearly, observations from standard meteorological stations are not suitable for estimating higher-elevation fog frequencies

FOG COLLECTIONS ROLE IN WATER PLANNING FOR DEVELOPING-COUNTRIES

In certain locations, the combination of meteorological conditions and topography are such that persistent fogs cover coastal or interior mountains. The droplets from these fogs are collected by trees or other tall vegetation. They can also be collected by appropriately designed man-made collectors, to provide large volumes of water for domestic, agriculture or forestry uses. The largest project to date has provided, since March 1992, an average of 11 000 litres of water per day (l/d) to a village of 330 people in the arid coastal desert of northern Chile. This project and others are reviewed. The impact of the deforestation of high elevation areas, and the subsequent loss of fog water input in a watershed are discussed, as are guidelines for water planners

A PROPOSED STANDARD FOG COLLECTOR FOR USE IN HIGH-ELEVATION REGIONS

The collection of fog droplets by vegetation is an important wet deposition process. It can, in fact, dominate the chemical and hydrological input to certain high elevation watersheds. However, measurements of fog deposition are rarely made and, where they do exist, comparisons of deposition rates in different locations have been hampered by the use of innumerable types of collection devices. A simple, inexpensive, 1-m(2) fog collector that can produce measurements of the deposition of fog water to a vertical surface is described here. The collector has been used successfully in five countries to investigate the variation of fog deposition in complex terrain and to estimate the deposition to trees and to much larger fog collectors. It is proposed that it be employed widely as a standard to quantify the importance of fog deposition to forested high, elevation areas and to measure the potential collection rates in denuded or desert mountain ranges.The standard fog collector costs about the same as a rain gauge ($100 U.S.) to construct and can be used with a variety of recording devices. It is a flat panel made of a durable polypropylene mesh and mounted with its base 2 m above ground. Fog collection rates are typically 1-10 L m(-2) of vertical collecting surface per day but can reach values of 30-40 L m(-2) day(-1). The presence of drizzle or light rain with the fog, coupled with 10 m s(-1) winds, has produced collection rates as high as 300 L m(-2) day(-1). If a standard fog collector is installed at a site with wind speed measurements and a conventional rain gauge, a reasonable estimate can be made of the proportions of fog and rain being deposited on the vertical mesh panel. This information is fundamental to the understanding of acidic wet deposition at higher elevations and to comprehensive hydrological calculations in watersheds

FOG-WATER COLLECTION IN ARID COASTAL LOCATIONS

The recent success of a large-scale pilot project to collect fog-water in northern Chile, indicates that this is a resource that should be serioulsy examined for use in certain semi-arid and arid regions of the world. Fifty 48 m2 collectors at a site in Chile have produced an average of 7200 L of water per day during three drought years. This paper reviews the fog-water collection process and lists 47 arid locations in 22 countries on 6 continents where collection of fog-water by vegetation or artificial collectors has been documented. One of the most exciting aspects of this resource is that in many regions the supply of water will be limited only by the number of collectors one chooses to install. In addition, since the source of the fog is normally the movement of marine stratocumulus decks over coastal mountains, the water quality is good and the water can be used for drinking and for other domestic and agricultural purposes

Fog as a Fresh-Water Resource: Overview and Perspectives

The collection of fog water is a simple and sustainable technology to obtain fresh water for afforestation, gardening, and as a drinking water source for human and animal consumption. In regions where fresh water is sparse and fog frequently occurs, it is feasible to set up a passive mesh system for fog water collection. The mesh is directly exposed to the atmosphere, and the foggy air is pushed through the mesh by the wind. Fog droplets are deposited on the mesh, combine to form larger droplets, and run down passing into a storage tank. Fog water collection rates vary dramatically from site to site but yearly averages from 3 to 10 l m(−2) of mesh per day are typical of operational projects. The scope of this article is to review fog collection projects worldwide, to analyze factors of success, and to evaluate the prospects of this technology