| Dew is an important source of moisture for plants living in semi-arid regions such asthe typical rain-fed jujube forest of the Loess hilly area (Mizhi County) in semi-arid loessplateau in China. However, information regarding dew in this region is scarce. Study on thecondition of dew formation and dew amount will be helpful for assessing ecological effectsof dew and significant to revealing physical mechanisms of dew formation on plantations inthe loess hilly region. In this study, the impact of leaf inclination, temperature and dew point-leaf temperature depression on the rate and quantity of dew accumulation on leaf surfaceindoor simulation were analyzed. In field measurement, sensitivity of meteorological factorsto dew amount in micro-scale was analyzed by path analysis, the parameters of empricalmodels (RH and DPD) were selected in different scale, and the dew amount and conditionof dew formation were investigated, the long-term trend of dew amount were alsocalculated (in1970-2005). The main conclusions of this study were as follows:（1）the accumulation rate and the maximum volume of dew on leaves decreased withthe increasing of leaf inclination while they increased with the increment of dew point-leaftemperature depression, ambient temperature and relative humidity. Under the horizontalconfiguration, leaf surface dew linearly accumulated soon over time to a stable value untilthe maximum volume (0.8mm) was reached. However, dew would fall down after reachingthe maximum volumn when the leaf inclination exists (45°or90°), which significantlyslowed down the accumulative rate and the zigzag pattern for the dynamic of dewaccumulati on appeared.（2）The results of path analysis on relevant factors in hours and minutes indicated thatdifferences existed in sensitivities of different factors to dew amount in different time scales.In the scale of minutes, the order of significant factors in sensitivity was: T> VPD> DPD>RH, while, In the scale of hours, it was: RH> VPD> μ> DPD> T. For VPD and DPD, nomatter in the scale of minutes or hours, they had weak sensitivities on dew amount. But forother factors, there were obvious scale effect, so pushing up or pushing down simply betweenscals are unreasonable.（3）Model parameters are different in the different time scales. At the interval of15 min, the parameters of RH and DPD models were78%and1oC,5oC; At the interval of30min, the parameters of RH and DPD models were76%and1oC,5oC; At the interval of1h,the parameters of RH and DPD models were74%and1oC,5.5oC. At the interval of15min and30min, Using the above model can predict accurately the dew duration, but at theinterval of1h, prediction accuracy of DPD model is higher than that of RH model.（4）The relative humidity>78%or1-3oC difference between air temperature and dewpoint temperature at the interval of15minutes significantly favored dew formation.（5）The average daily dewamount was0.75mm, the cumulative daily dew amount was83.03mm (13.01%of the precipitation), the number of heavy dew days was92days (85.18%of all the dewing days), and the dewing day number with a daily dew amount excessed thesize of the canopy reservoir for free water, was79days (73.15%of all the dew days); and dewwas characterized by high frequency and strong stability;（6）Over the past35years, the total dew day number between June and Octobertended to vary similarly to the total rainy day numbers during the same period of time. Inthe jujube plantation, the total dew amount over the years in question was2281.5mm. Thestudy showed that in the rain-fed jujube plantation dew as important part of water resourcesthat should not be ignored could significantly affect regional water balance. By the way, thestudy was positive significant for further studying dew formation mechanism in plantations. |
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