In a desert, dew can serve as an important source of moisture for small animals, plants, and biological crust development. Parts of desert sand dunes can be covered by a thin intact surface layer formed by biological activity. The existence of such a layer is very important as it can help to initiate or enhance sand dune stability. Dewfall at night is a process whereby moisture from the atmospheric water reservoir is deposited on the earth's surface. The goal of the present research was to observe and measure dew amounts in the Nizzana sand dune experimental station, located in the northwestern Negev desert of Israel, and to model both this process in detail as well as early morning drying.
In September 1997, a measurement programme was carried out in which the energy budget at the desert surface was monitored. Here, special attention was focussed on the night- time (dew-fall period) and early morning (drying period) sensible and latent heat transports. With the eddy correlation technique both convective transports are estimated in a direct way. Moreover, with a scintillometer sensor, the spacial averaged convective sensible and latent heat transports were estimated over a distance of about 200 m. At the surface, using small micro- lysimeters, the water budget of the first 3 cm depth of the ground, including the biological crust layer, was assessed. A newly-developed optical remote dew sensor was used to measure surface wetness continuously during the study period.
Model simulations have been carried out to obtain more insight into the evening dewfall and early morning drying process, as well as the water collection process in the top soil surface layer.