Exploring fog as a supplementary water source in Namibia
Introduction
The Namibian coastal region is a hyperarid environment where sources of freshwater are scarce. Fog occurs on 60–200 days per year along the coast and extends for some distance inland. Fog precipitation exceeds rainfall and is therefore a more reliable source of water than rainfall for the desert fauna and flora, and it could also be used as a supplementary source of water for human settlements in this area Lancaster et al., 1984, Pietruszka and Seely, 1985, Henschel et al., 2000.
The ecological implications and uses of fog by fauna and flora of the Namib Desert have been investigated for some time (e.g., Hamilton and Seely, 1976, Seely et al., 1998). However, investigations of fog collection for water supply to human settlements in the Namib only started in 1995 (Henschel et al., 1998).
This paper presents an overview of the Namibian fog collection programme. It discusses the climatology and chemistry (major ion composition) of fog in the Central Namib Desert and the potential of fog collection for water supply to settlements in this area. The paper also discusses the feasibility of mixing fog water and saline groundwater in order to supply water of satisfactory quality for drinking purposes to settlements in the Namib Desert during seasons when the conventional groundwater sources display high salinisation. This approach to the use of fog water could contribute to a better diversification of alternative sources of freshwater in this area and could also be applicable to other fog-occurring desert environments where fog water is currently used for water supply.
Section snippets
Climate
Ninety-seven percent of Namibia is a hyperarid to semiarid environment (Hutchinson, 1995) (Fig. 1).
The Namib Desert is the most arid part of the country and rainfall is low and highly variable in time and space Lancaster et al., 1984, Henschel et al., 2000. Average annual rainfall is 18 mm at the coast at Swakopmund and is 21 mm at 56 km inland at Gobabeb Nagel, 1959, Lancaster et al., 1984 (Fig. 1). However, it is common to experience consecutive years without rain, for instance, Swakopmund
Fog collection
The results of fog collection experiments with SFCs from 1996 to 1997 at the sites inland indicate a seasonal variation in fog frequency with most fog occurring from August to February (Fig. 3).
The daily average fog collection at the test sites was 508 ml/m2/wet day at Gobabeb, 3308 ml/m2/wet day at Klipneus and 2390 ml/m2/wet day at Swartbank. Fog collection throughout the test period, including days without fog, was 104 ml/m2/day at Gobabeb, 1074 ml/m2/day at Klipneus and 774 ml/m2/day at
Conclusions
In conclusion, it appears that despite the poor quantity and quality of traditional sources of freshwater in the central Namib, there are possible solutions to alleviate the water scarcity. Fog is a viable source of water that can supplement traditional sources in rural settlements and perhaps urban water supply schemes in the Namib Desert. The timing of high groundwater salinity and peak fog deposition in the Namib Desert is most favourable for dilution of saline groundwater for drinking
Acknowledgements
We thank Namwater, particularly Mrs. Merylinda Conradie, for the chemical analysis, as well as Mr. Vilho Mtuleni and the other members of the staff of the Desert Research Foundation of Namibia for the assistance with data collection. We are also grateful to Ms. Annabel Smith, a student at Royal Holloway University (Britain), for editing this manuscript. The University of Namibia provided logistic support during fieldwork at its Henties Bay Campus.
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