Dewfall measurements on Lanzarote, Canary Islands

At Lanzarote, Canary Islands, condensation is considered to play a significant role in the water budget of fields mulched with porous volcanic products ("Picon"). Here, 68 nights of gravimetric condensation measurements with mulched and bare surfaces, along with meteorological measurements were carried out. Results presented here indicate two major findings of interest with respect to general assumption: Firstly, nocturnal condensation on the mulch surface is lower than on a dry bare (loam) soil surface. A slightly higher nocturnal cooling of the mulched surface, and resulting higher dewfall in the strict sense, is overcompensated by the stronger hygroscopic properties of the soil. Secondly, dewfall, though otherwise consistent in magnitude and meteorological dependency with empirical and theoretical knowledge in literature, can still be observed at high wind speeds (u approximate to 10 m s(-1) at 10 m a.g.l.) in northern to north-eastern trade winds that carry moist air from the sea. Dewfall to the mulched surface was observed in 39 of the measurement nights with a mean nocturnal sum of 0.07 mm.