Condensation Process Of Water Vapour On Plant Leaf In The Loess Hilly And Gully Region Of China

Water is one of the main factors limiting vegetation growth Condensation plays an important role as a non-precipitation input to the hydrological cycle and vegetation recovery in semi-arid ecosystems.To clarify the process and characteristics of water vapor formation on plant leaves,this paper investigates the condensation characteristics of typical plant leaves in the loess hilly and gully region of China,analyses the amount of condensation on Ulmus pumila L,Hippophae rhamnoides Linn and Tribulus terrestris L leaves through field measurements and simultaneous LWS observations and simulates the process of water vapor condensation on leaves using the BEYSENS model.The main conclusions are as follows:（1）The relationship between the leaves of typical plants such as Ulmus,Tribulus,and Hippophae and the LWS observations can be expressed as W_d=AU^B,with the corresponding parameters being,respectively,Ulmus:A=1.5×10^-11,B=3.316,Hippophae:A=3.5×10^-10,B=2.883,Tribulus:A=4.1×10^-7,B=1.99.Based on the above equation,the cumulative condensation on the foliage of typical plants such as elm,buckthorn,and thistle from the spreading to the withering stage in 2022 was obtained as follows:6.42 mm,9.20 mm,and 18.31mm,respectively.（2）The daily dynamics of water vapor condensation on plant foliage is characterized by a maximum daily duration of 10.5h,with the cumulative condensation increasing for 70%of the continuous periods and decreasing for 30%of the periods,with condensation peaking around sunrise.（3）The frequency of condensation of water vapor is high from July to October,reaching more than 60%per month and even 90%in September.In the case of Tribulus Terrestris leaves,the maximum monthly condensation in 2020-2022 is 4.14 mm,3.76 mm,and 5.28 mm,the annual condensation is 21.86 mm,17.05 mm,and 20.03 mm,and the dew-to-rain ratio is 3.03%,2.44%,and 2.82%,the annual occurrence（frequency）of condensation is 187 days（51.2%）,163days（44.7%）and 162 days（44.4%）respectively,which shows that condensation is an indispensable source of non-precipitation recharge for the local ecosystem.（4）The condensation of water vapor is relatively high at 0.6m above ground level,decreasing with increasing height,and is more likely to occur in the ranges of temperature,relative humidity,wind speed,temperature dew point difference,temperature,and foliage temperature difference of 5—10°C,80%—100%,0—2 m/s,0—0.3°C,±0.3℃range are more prone to condensation.（5）The D-BEYSENS condensation assessment model is used to calculate water vapor condensation in the Loess Hills and Gullies,and a comparison with actual observations shows that the underestimation of condensation yield for more dew events and the overestimation of condensation yield due to the amplification of the frequency of smaller dew events compensate for each other.Therefore,the model is applicable to the prediction of condensation above the monthly scale,and the average annual cumulative condensation in the loess hills and gullies was verified to be 25 mm,with an increasing trend of interannual variation of condensation in the region.