Dew contribution to the water balance in a semiarid coastal steppe ecosystem (Cabo de Gata, SE Spain)

Dewfall deposition can be a significant source of moisture in arid and semiarid ecosystems, thus contributing to improve daily and annual water balances.. Occurrence, frequency and amount of dewfall were measured in the Balsa Blanca site (Cabo de Gata, Almeria, Spain) from January 2007 to May 2008. This area has a sparse vegetation cover dominated by Stipa tenaccisima combined with bare soil and biological soil crusts. Wetness sensors were used to detect occurrence and frequency of dew events. The single-source Penman—Monteith equation simplified for water condensation was used to calculate dew amount. Micro-meteorological conditions during dew formation were also measured. Dew condensation was recorded over 98% of nights during the study period. Dewfall length varied from 1 to 16 hours per day with an average of 6.3 ±0.5.hours per day. Average dew amount was 15.6±.0.34 g H2O m-2.h-1 showing a relatively small variability throughout the year. Therefore dew amount was mostly dependent on dew duration. Dew episodes were longer in late autumn and winter and decreases along spring. Annual dewfall was 30.5 mm in 2007, which represents 15% of total rainfall. 2007 was a relatively wet year with 280 mm rainfall. Comparing contribution of dew to the local water balance during a wet (January-May 2007, 120 mm rainfall) and dry period (January-May 2008, 15 mm rainfall), we have found a dew contribution of 15% in 2007 and 128% in 2008. These results highlight the relevance of dew as a relatively small but constant source of water in arid ecosystems, as well as its significant contribution to the local water balance mainly during dry periods.