Dynamics of Dew in a Cold Desert-Shrub Ecosystem and Its Abiotic Controls

Xiaonan Guo,Wei Feng,Bin Wu,Yuqing Zhang,Jing Xie,Tianshan Zha,Heli Peltola,Xin Jia,Jinnan Gong

doi:10.3390/atmos7030032

Xiaonan Guo, Wei Feng + Show 7 more

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https://doi.org/10.3390/atmos7030032

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Abstract

The temporal dynamics of dew formation in cold desert-shrub ecosystems are still poorly understood. We examined dew and its abiotic controls in a shrubland in northwestern China with continuous eddy-covariance measurements of latent heat fluxes gathered over the growing-season of 2012. The dew amount was larger in mid-summer than in spring and autumn, but the dew duration was shorter in summer (from ~10:00 p.m. to ~6:30 a.m.) than in spring and autumn (from ~8:30 p.m. to ~7:30 a.m.). Dew occurred on 85% (166 days) of growing-season days, with monthly means ranging from 0.09 to 0.16 mm day−1. Dew was dominantly and positively controlled by Relative Humidity (RH), which explained 89% of its variation. Soil heat flux (G), air temperature (Ta), wind speed (Ws), Soil Water Content (SWC) and Vapor Pressure Deficit (VPD) also influenced dew formation. The most favorable conditions for dew formation were at Ta < 17 °C and RH > 75%. The Penman–Monteith equation predicted actual dew reasonably well. The predicted growing-season dew amount (21.3 mm) was equivalent to 7.2% and 8.9% of corresponding rainfall and evapotranspiration, respectively. It is suggested that dew could be a stable and continuous source of water that helps desert plants survive during warm summers.

Highlights

Dew occurs when moist air condenses on a substrate [1,2], as its surface temperature falls below the dew point temperature
Eddy-Covariance method (EC) measurements of latent heat flux (LE) are subject to moderate uncertainty, and the measurement of nighttime flux is challenging [26,50], The EC technique fails during periods of low wind speed at night and routinely under measures of LE at higher wind speeds, with energy-closure fractions of less than one [46]
Eddy-covariance measurements of dew in a cold desert-shrub ecosystem in Ningxia, China, showed dew amounts ranging from 0.09–0.16 mmday1 over the growing season, with higher values in summer than spring or autumn

Summary

Introduction

Dew occurs when moist air condenses on a substrate [1,2], as its surface temperature falls below the dew point temperature. Dew can originate from three separate sources: air (dewfall), plant (guttation), and soil (dewrise) [3]. Sufficient moisture in the air and intensive radiative cooling of the surface are two basic requirements for the formation of dew [4]. Relative humidity directly affects atmospheric visibility and the formation of clouds, fog, and dew [3,5,6]. The formation of dew is indirectly affected by cloudiness [7], wind speeds, which may dampen the effect of radiative cooling by mechanically mixing the lower nocturnal boundary layer [1,8], soil water content [9], and the soil heat flux [6]. There have been relatively few studies on the abiotic controls of dew in cold desert-shrub ecosystems

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