Altitude dependent dew and fog in the Negev Desert, Israel

Dew and fog measurements at different altitudes were carried out in order to evaluate the impact of altitude upon dew and fog condensation in the Negev Desert, Israel. Measurements were taken along the 90-100 mm isohyet at Nizzana, Sede Boqer and Har Harif, approximately 250, 500 and 1000 m above sea level, respectively, during the late summer and fall of 1992. The data was compared to long term dew measurements which were carried out during 1987-1994 in Sede Boqer and during 1990-1995 in Nizzana. Average dew and fog amount increased with elevation despite the greater distances from the sea of the more elevated sites and consequently their lower moisture supply. Thus, an increase in approximately 0.015 and 0.03 mm in the average daily dew and fog amounts, respectively, per 100 m increase in elevation is expected, resulting in a 2 to 3-fold increase in average daily dew and fog amounts from sea level to 1000 m above m.s.l. An increase in the percent of days with heavy dew or fog with altitude was also noted. The data, thus, indicate the important effect of topographical elevation upon dew and fog precipitation in the Negev and may assist in evaluating the role of dew in plant yield under natural conditions and upon agricultural practices. (C) 1999 Elsevier Science B.V. All rights reserved.