干旱区生态环境知识资源中心

Non-rainfall events like dew or hoar frost formation are often neglected in the water budget, because either assumed to be too small or their determination requires time consuming and difficult measurements. These events supply in many dryland ecosystems a substantial amount of water, but their role for northern humid ecosystems is largely unknown. There is a general need to quantify the ecological relevance for ecosystems of the water amount from dew and hoar frost formation. Weighable precision lysimeters were used to determine dew and hoar frost formation for a low mountain range and alpine grassland site for the hydrological years 2013-2015.

Together dew and hoar frost formation ranged on a yearly basis between 42.1 and 67.7 mm, which corresponds to 4.2-6% of the total annual amount of precipitation. In drier months dew and hoar frost contributed up to 16.1% of total monthly precipitation amount. In winter months dew and hoar frost formation contributed up to 38% to the total monthly precipitation amount. Our investigation suggests, that dew and hoar frost formation are of ecological importance during droughts as well as cold periods. The amounts and seasonal patterns of dew and hoar frost formation could be predicted relatively well, based on standard meteorological variables with the Penman-Monteith equation. However, our results also showed, that the surface energy balance model from Penman-Monteith underestimated the amount of dew and hoar frost during colder periods and specific meteorological site conditions (i.e. high wind speeds at night). The mean underestimation between calculated and measured dew and hoar frost on a yearly scale were 63.2% and 16.6% at Rollesbroich and Gumpenstein, respectively. Dew and hoar frost formation contributes substantially to the water budgets of a low mountain range and alpine grassland.