Analysis of dew precipitation in three habitats within a small arid drainage basin, Negev Highlands, Israel

Water availability is the most important limiting factor in arid lands. Any additional source of water, such as dew and fog, may have a positive impac t upon the ecosystem. Dew and fog precipitation are largely dictated by wea ther conditions and habitat. Dew and fog measurements were carried out for 29 days in the fall of 1987-1 989 at three distinctive habitats within a single drainage basin in the Neg ev Highlands, Israel. The habitats were a sun- and wind-exposed habitat, at two hilltops, a sun-shaded habitat, at the north- and west-facing footslop es, and a wind-protected habitat, at two wadi beds. Morning weather conditi ons (cloudiness, wind speed) were also monitored. An analysis of the dew an d fog quantities and duration was performed. Clear mornings and a single foggy morning recorded were characterized by hi gh dew and fog amounts and duration, whereas lower values were recorded dur ing cloudy and especially windy mornings. The hilltop stations and especial ly the sun-shaded footslope stations obtained significantly higher values o f dew and fog for a significantly longer duration than the wadi bed station s. Whereas the results did not support the hypothesis that advective conden sation is responsible for the high dew amounts at the sun-shaded habitat, t he data showed a continuous dew condensation even after sunrise. This conti nuous condensation, averaging up to 1.1 h following sunrise, was especially pronounced at the sun-shaded habitat and may explain the higher dew values and longer time duration obtained at this habitat. Since maximal dew value s may not necessarily be obtained at sunrise and may change according to ha bitat, dew collection time should be carefully considered. (C) 2000 Elsevie r Science B.V. All rights reserved.