LAUSR

Abstract Dew has been recognized as an important source of water for many coastal arid and semiarid ecosystems because of its contributions to daily, seasonal and annual water balance. We measured the frequency, duration and amount of dewfall from January 2011 to December 2016 to assess its contribution to the local water balance in a continental semiarid grassland where Bouteloua gracilis (Blue grama) is the key grass species. Dew was observed with leaf wetness sensors and amounts were estimated with an energy model using micrometeorological data. Dewfall occurred on 39% of the nights with an average duration of 5 ± 4 h. Daily average dewfall deposition during the study period was 0.2 mm with the highest accumulation of 0.7 mm. Annual dewfall ranged between 16.5 and 69 mm, therefore representing between 4.9% and 10.2% of annual precipitation. Dewfall contributed between 7.6% and 33.6% of the total dry season precipitation (winter/spring), which considerably reduced the water deficit. Our results highlight the relevance of dewfall as a consistent and important water source in this semiarid grassland ecosystem. It is of particular importance during dry periods, where it may represent the only water source available to the vegetation at this site.