Dew measurement and estimation of rain-fed jujube (Zizyphus jujube Mill) in a semi-arid loess hilly region of China

Wang, Xing; Gao, Zhiyong; Wang, Youke; Zhi, Wang; Jin, Shuanggen

doi:10.1007/s40333-017-0061-z

Cited by 17 publications

(14 citation statements)

References 37 publications

(52 reference statements)

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“…Additionally, sites with a high elevation like MOAB (1779 m), ONAQ (1662 m) and RMNP (2742 m) are associated with cold and dry air due to the low pressure. The relative humidity within the canopy of the forests is usually higher than the grasslands at night (86 ± 9 % vs. 76 ± 15 %, 1 SD) not only because of a denser canopy structure but also because forests occur in wetter regions than grasslands (Woodward et al, 2004). The two exceptions here are the grasslands LAJA and DSNY, which present tropical characteristics (RH = 95 ± 3 %, 1 SD).…”

Section: Sitesmentioning

confidence: 69%

Dew frequency across the US from a network of in situ radiometers

Ritter

Berkelhammer

Beysens

2019

Hydrol. Earth Syst. Sci.

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Abstract. Dew formation is a ubiquitous process, but its importance to energy budgets or ecosystem health is difficult to constrain. This uncertainty arises largely because of a lack of continuous quantitative measurements on dew across ecosystems with varying climate states and surface characteristics. This study analyzes dew frequency from the National Ecological Observatory Network (NEON), which includes 11 grasslands and 19 forest sites from 2015 to 2017. Dew formation is determined at 30 min intervals using in situ radiometric surface temperatures from multiple heights within the canopy along with meteorological measurements. Dew frequency in the grasslands ranges from 15 % to 95 % of the nights with a strong linear dependency on the nighttime relative humidity (RH), while dew frequency in the forests is less frequent and more homogeneous (25±14 %, 1 standard deviation – SD). Dew mostly forms at the top of the canopy for the grasslands due to more effective radiative cooling and within the canopy for the forests because of higher within the canopy RH. The high temporal resolution of our data showed that dew duration reaches maximum values (∼6–15 h) for RH∼96 % and for a wind speed of ∼0.5ms-1, independent of the ecosystem type. While dew duration can be inferred from the observations, dew yield needs to be estimated based on the Monin–Obukhov similarity theory. We find yields of 0.14±0.12mmnight-1 (1 SD from nine grasslands) similar to previous studies, and dew yield and duration are related by a quadratic relationship. The latent heat flux released by dew formation is estimated to be non-negligible (∼10Wm-2), associated with a Bowen ratio of ∼3. The radiometers used here provide canopy-averaged surface temperatures, which may underestimate dew frequency because of localized cold points in the canopy that fall below the dew point. A statistical model is used to test this effect and shows that dew frequency can increase by an additional ∼5 % for both ecosystems by considering a reasonable distribution around the mean canopy temperature. The mean dew duration is almost unaffected by this sensitivity analysis. In situ radiometric surface temperatures provide a continuous, non-invasive and robust tool for studying dew frequency and duration on a fine temporal scale.

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Section: Sitesmentioning

confidence: 69%

Dew frequency across the US from a network of in situ radiometers

Ritter

Berkelhammer

Beysens

2019

Hydrol. Earth Syst. Sci.

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“…As for the desert ecosystem, low frequency of rainfall, light rain, short duration and intense evaporation during the day in desert ecosystems make it impossible for desert organisms to obtain a water supply over a long period. Thus, it is very difficult for desert plants to absorb water through their roots due to prolonged soil moisture deficiencies [29]. Leaf water absorption is very important, and micro dew can also be absorbed directly by plant leaves [11].…”

Section: Discussionmentioning

confidence: 99%

“…The difficulty of dew measurement is both in the definition of dew and in its actual measurement. However, scholars have developed various dew measurement instruments or methods in the past 70 years, including dew gauge [23], electrical resistance sensor [24], hiltner-type dew balance method [25], soil moisture sensor [1], leaf wetness sensor [26][27][28][29][30], artificial condensation surface method [31][32][33][34], and weighing method [6,12,35,36]. The last three items of the methods mentioned above are widely used.…”

mentioning

confidence: 99%

“…The last three items of the methods mentioned above are widely used. For example, materials (tissues, woods and plastic) were weighed before and after the dew event to calculate the dew yield [17], high precision lysimeters were weighed to obtain dew formation at night on natural ecosystems [37] and a leaf wetness sensor was used to estimate the presence or absence of wetness on its surface [26], which can also be calibrated to provide a potential dew yield [29,30,38,39].…”

mentioning

confidence: 99%

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Dew Yield and Its Influencing Factors at the Western Edge of Gurbantunggut Desert, China

Jia

Zhao

2019

Water

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Dew is a significant water resource in arid desert areas. However, information regarding dew is scarce because it is difficult to measure due to the harsh environment of locations such as Gurbantunggut Desert, China. In this study, a non-destructive field experiment was conducted from 2015 to 2018 at a desert test station located in the western edge of the Gurbantunggut Desert, using a calibrated leaf wetness sensor (LWS) to measure dew yield. The results are as follows: (1) Dew formed after sunset with the atmospheric temperature gradually dropping and evaporated after sunrise with the temperature increasing in the second morning. (2) Dew was featured as ‘high frequency and low yield’. The average daily dew yield during dew days was 0.10 mm with a daily maximum of 0.62 mm, while dew days accounted for 44% of the total monitoring days, with a monthly maximum of 25 days. Compared with rainfall, dew days were two times as frequent as rainy days, while the average annual dewfall (12.21 mm) was about 1/11th of the average annual rainfall (134.6 mm), which indicates the dew contribution to regional water balance is about 9%. (3) March–April and October–November are the main periods of dew occurrence in this region because accumulated snow begins to melt slowly in March–April, providing sufficient vapor for dew formation, and the air temperature difference between day and night in October–November is the highest in the year, meaning that the temperature drops rapidly at night, making it easier to reach the dewpoint for vapor condensation. (4) Daily dew yield (D) was positively correlated to relative humidity (RH) and the difference between soil temperature at 10 cm below the ground and surface soil temperature (Tss), and negatively correlated to wind speed (V), air temperature (Ta), surface soil temperature (Ts), cloud cover (N), dewpoint temperature (Td) and the difference between air temperature and dewpoint temperature (Tad). It should be noted that the measured values of all factors above were the average value of the overnight period. The multivariate regression equation, D = −0.705 + 0.011 ×RH− 0.006 ×N− 0.01 × V, can estimate the daily dew yield with the thresholds of the parameters, i.e., RH > 70%, N < 7 (oktas) and V < 6 m/s.

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“…Water 2019, 11,126 3 of 18 a temperature inversion occurred between the heights of 1 m and 4 m [10]. In Mizhi experimental station, located in the middle of the Loess Plateau, observations showed that dew occurred when the relative humidity was >78%, wind speed <0.5 m/s, and dewpoint depression (difference between air temperature and atmospheric dew point temperature) was about 1-3 °C [35]. The degree of influence on dew formation is different when the same factors act in different geographical areas.…”

Section: Measurement Sitementioning

confidence: 99%

Characteristics of Dew Formation in the Semi-Arid Loess Plateau of Central Shaanxi Province, China

Jia

Zhi

Wang

2019

Water

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Compared to rain, dew is an important supplementary source of water for the survival of certain plants and animals in drylands. However, the hydrology of dew has not yet been fully investigated due to difficulties in measuring the amount and duration of it. In this study, a 3-year in-situ monitoring experiment was conducted from 2014 to 2016 in the semi-arid Sanyuan County, Shaanxi Province of China, using a leaf wetness sensor (LWS) and four associated meteorological instruments. Results showed that the average annual total dewfall was 32.8 mm with a daily maximum of 0.88 mm. The majority of daily dew occurred in the night from 18:00 to 8:00 with the maximum condensation rate occurring at around 4:00. The maximum dew residence time was about 18 h/day on the dew days in all seasons. However, the actual dew production period was about 14 h in spring (March–May), autumn (September–November), and winter (December–February), and only 11 h in summer (June–August). The maximum intensity and amount of dew always occurred in autumn (with an average amount of 12.2 mm or 37% of the annual total), followed closely by spring (11.4 mm, 35%), with much less in summer (6.6 mm, 20%) and winter (2.6 mm, 8%). The annual dew distribution by months showed a double crest variation, with two peaks in April–May and October–November, and two valleys in January–February and July. Comparatively, annual dewfall is only about 1/18th of the rainfall in this region, but the number of dew days (224 days, or 61% of year) is 2.6 times that of rain days (87 days, 24%), making dew a critical supplementary source of water for mitigating dry periods and supporting native plants and animals. Rain and dew are highly complementary as dew occurs in cloudless nights while the rain occurs in different and on much fewer occasions in the region. The dew amount was highly and positively correlated to the relative humidity of the air above the threshold of 81% (r = 0.78, p < 0.01), negatively correlated to the difference between air temperature Ta and dewpoint Td, when (Ta − Td) is less than 4 °C (r = −0.66, p < 0.01), and weakly correlated to wind speed (0.2 to 2 m·s−1), wind direction, surface soil moisture, and temperature. In the Sanyuan region, two general wind directions, 30°–90°and 210°–270°, were more favorable for the formation of dew.

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Dew measurement and estimation of rain-fed jujube (Zizyphus jujube Mill) in a semi-arid loess hilly region of China

Cited by 17 publications

References 37 publications

Dew frequency across the US from a network of in situ radiometers

Dew frequency across the US from a network of in situ radiometers

Dew Yield and Its Influencing Factors at the Western Edge of Gurbantunggut Desert, China

Characteristics of Dew Formation in the Semi-Arid Loess Plateau of Central Shaanxi Province, China

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