To conceive a sustainable development in arid regions of the world is a difficult task due to the lack of water and extreme fragility of the environment. Often these areas have important natural resources that cannot be used due to water shortage. Solar radiation and wind are abundant and propitious for clean and productive energy; the elements of climate, temperature and humidity usually are of great benefit for agriculture; in the Chilean case, rich minerals, such as copper, gold, silver, iron and nitrate are found in abundance, as well as the cold marine waters, rich in oxygen and nutrients allow a varied fauna and flora. Nevertheless, the environment is a big empty space. People live in large cities and there are only few rural settlements with small population (3% rural). History has shown until now, that these natural resources do not permit a sustainable development when water is not easily available. In the case of minerals and fishery, once the resource is exhausted or the prices are not suitable, the coves, camps, towns or cities are abandoned and the progress achieved usually changes into a miserable empty environment. That is the Chilean reality in the big “pampas”, in the coast and in the mountains of Atacama Desert, where many phantom towns are scattered along the old dirt roads. People then migrate to cities and engross the marginal suburbs and slum areas, where the quality of life is very poor. To avoid this situation or at least diminish these effects, a development of rural areas based in more than one resource should be in the mind of planners. The use of the natural resources with alternative technologies may give the possibilities to have a development with social justice and economical and environmental viabilities. The big deserts located in the western coasts of the continents usually have frequent fog. It is an advective cloud generated in the sea that rolls into the littoral plains and mountains that give moisture to the soils and in some cases allow vegetation and fauna. The importance of fog in arid ecosystems and as an economical and social water resource Pilar Cereceda*, Pablo Osses, Felipe Osses, Horacio Larrain, and Martín Farías Instituto de Geografía Pontificia Universidad Católica de Chile 1. Introduction: To conceive a sustainable development in arid regions of the world is a difficult task due to the lack of water and extreme fragility of the environment. Often these areas have important natural resources that cannot be used due to water shortage. Solar radiation and wind are abundant and propitious for clean and productive energy; the elements of climate, temperature and humidity usually are of great benefit for agriculture; in the Chilean case, rich minerals, such as copper, gold, silver, iron and nitrate are found in abundance, as well as the cold marine waters, rich in oxygen and nutrients allow a varied fauna and flora. Nevertheless, the environment is a big empty space. People live in large cities and there are only few rural settlements with small population (3% rural). History has shown until now, that these natural resources do not permit a sustainable development when water is not easily available. In the case of minerals and fishery, once the resource is exhausted or the prices are not suitable, the coves, camps, towns or cities are abandoned and the progress achieved usually changes into a miserable empty environment. That is the Chilean reality in the big “pampas”, in the coast and in the mountains of Atacama Desert, where many phantom towns are scattered along the old dirt roads. People then migrate to cities and engross the marginal suburbs and slum areas, where the quality of life is very poor. To avoid this situation or at least diminish these effects, a development of rural areas based in more than one resource should be in the mind of planners. The use of the natural resources with alternative technologies may give the possibilities to have a development with social justice and economical and environmental viabilities. The big deserts located in the western coasts of the continents usually have frequent fog. It is an advective cloud generated in the sea that rolls into the littoral plains and mountains that give moisture to the soils and in some cases allow vegetation and fauna. One aspect that has not been sufficiently studied is the role that fog plays in the natural environment and ecosystems of deserts and semi deserts, specially the amount of water that is used by plants and animals from this resource. There are important studies done from the botanical point of view of this foggy environments, and usually there is no doubt that fog is the element that maintains the flora and fauna; nevertheless, how much water there is in the fog, how much water a plant is capable to intercept and use, how animals acquire and use its water, are some of the questions that still need a response. The ecosystems that survive in these areas are called fog oasis. They are located in a very fragile environment, many times are relicts of vegetation that lived in the past with much more water and maintain them solely by the presence of fog. A rich variety of species is present in these ecosystems, they survive during long dry periods. Important occasional rains occur every so often, usually due to the El Niño Southern Oscillation phenomenon.FONDECYT53FONDECYT