Dew measurement by Eddy covariance and wetness sensor in a semiarid ecosystem of SE Spain

Summary Information regarding dew precipitation is scarce, both because it is considered a minor component of the water balance and because it is difficult to measure. Nevertheless, although yielding relatively low amounts of water, dew can be of great importance for the local water balance in semiarid and arid environments. The aim of this study was to explore the adequacy of the Eddy Covariance technique, combined with qualitative methods (such as wetness sensors), as a tool to measure actual dew in semiarid conditions. This technique was used to assess the relative contribution of dew to the local water balance in a dry river bed representative of semiarid environments (Rambla Honda, Tabernas) located in the Almeria province (SE Spain). Results show that an accurate filtering and management of data from Eddy Covariance (EC) combined with the records of the wetness sensors (WS), allowed us to generate a data base which can be used to develop and parameterize theoretical or empirical dew deposition models. We found that a simple equation for potential dew predicted adequately actual dew for the study area, and permitted us to estimate a dew contribution of 13 mm from February to June 2003, which accounts for 12% of the rainfall for the same period. Dew deposition was higher in late winter and early spring, when vegetation starts to grow actively. In consequence, this additional input of water can be of great relevance to the local water balance especially during dry years.