The Difference Study Of Local Climate On Artificial Shelter Forest Land And Natural Sandy Land In Taklimakan Desert Hinterland

The climate over the Taklinakan Desert is extremely arid.As the establishment of oil base,a total of 2km artificial green vegetation land(hereafter,AGVL)have beenformed in the sand dune.Due to the change of properties of underlying surface,and the following chain reaction of meteorological characteristic parameters,the structure of energy distribution near the stratum is changed,and the strong contrast between local climate and desert climate is formed.Therefore,it is necessary to study the varied interval of threshold of meteorological factors and regional climate characteristics of AGVL under the background of desert,and the difference of flux parameters between AGVL and natural sandy land(hereafter,NSL)as well as the response of important parameters of land surface process to local climate of AGVL need to be of comprehensive evaluation and in-depth analysis.For this purpose,weobtain the synchronous observation data of AGVL and NSL during the growing season,using high-precision observation instruments and advanced experimental methods.Meanwhile,in view of the edge effect of AGVL,intensified observation experiments are carried out synchronously.The discrepencyof local climate of underlying surface are quantitatively analyzed by the some methods such as theoretical research,experimental data analysis and numerical simulation.Furthermore,we have revealed the mechanism of the phase difference of sensible and latent heat with the time distribution.We also conduct a parameterized comparsion and analysis between the simulated measurments of land surface process and actual measurments,and evaluate the response of parameterized scheme to local climate.Our study provides scientific experimental data that support for sustainable development of AGVL in desert region.Besides,our research also provide important reference and research basis for the land-atmosphere interaction and influence mechanism between Desert-oasis region.The mainly obtained results are as follows:1)From sunrise to noon,the increasing rate of temperature in NSL is higher than that in AGVL,and the opposite results occur between noon and sunset.The temperature of AGVL was 2 hours later than that of NSL.At night,the boundary temperature of AGVL is generally higher than that of NSL and the central area of AGVL.In addition,under the combined influence of different underlying conditions,local circulation and small terrain,the results are as follows:AGVL(middle)daily range>NSL(west)>AGVL(east)>AGVL(west).AGVL is obviously shorter than NSL in the period of positive temperature change in four seasons.On the other hand,temperature inversion occur at night for four seasons.In winter,the intensity of temperature inversion is the highest in January,and the maximum difference is 12.8?,followed by autumn,the third in spring,the smallest in summer,and the maximumdifference is 6.4?.2)Seasonal variation of mean wind speed:the largest in spring,the second in summer,the third in autumn and the smallest in winter.The wind speed in daytime is larger than that in night,and the wind speed in NSL is larger than that in AGVL.In spring,the average diurnal wind speed difference of NSL is 3 m/s,the center of AGVL is 1.8 m/s,and the East-West boundary of AGVL is 2.0 m/s and 2.2 m/s,respectively.In spring,the average wind speed of NSL is quantified to 1 m/s,the decreasing rate of the boundary wind speed of AGVL is 35%,and the decreasing rate of the central wind speed of AGVL is 68%.In summer,the decreasing rate of wind speed at the boundary of AGVL is 30%,and that at the center of AGVL is 71%.3)Potential evapotranspiration FAO56-PM is suitable for AGVL under the background of arid region.The calculated values are linearly correlated with the observed values.The correlation coefficients are as follows:AGVL(middle)0.933,AGVL(east)0.943 and AGVL(west)0.942,respectively.The difference between saturated water vapor pressure and actual water vapor pressure,the average temperature of 2 m,the average wind speed of 2 m and the slope of saturated water vapor pressure are the main factors,which affect the calculation of evapotranspiration.4)In NSL and AGVL,the diurnal variation of radiation components was significant.DR(total solar radiation)and UR(reflected radiation)have the peak value in summer,presenting the increased trend in winter-spring-summer,and decreased trend in summer-autumn-winter.The difference interval of ULR(ground long wave radiation)between NSL and AGVL ranges from-30-20 W/m².On the other hand,the change of soil moisture is one of the main reasons for the difference of surface albedo between AGVL and NSL.Drip irrigation in AGVL in Taklimakan Desert increases soil moisture content,which has a lagging effect on the surface and affects the monthly change of surface albedo.The main energy consumption forms of net radiation are H(sensible heat flux)and G₀(surface soil heat flux),where H is the largest and LE(latent heat flux)is the smallest.At night,G₀ is the main form of energy consumption.Conversely,H energy consumption is the main form during the daytime.Under the environment of Taklimakan Desert,the energy distribution pattern of AGVL is basically consistent to NSL.However,in vegetation growing season and flourishing season,the share of flux consumption for LE will increase,and the energy consumption ratio will increase by about 1.5%.5)The unclosed rate of NSL and AGVL is over 50%in winter,and the fitting coefficient of AGVL is very low.In other seasons,the unclosed rate of AGVL is better than that of NSL,which is also a reflection of the smaller value of D(surface energy residual).However,due to the fluctuation of small terrain and the influence of underlying surface conditions,there are obvious differences in the closure of AGVL and NSL.6)Radiation simulation validation:The accuracy of the model for NSL radiation simulation is higher than that of AGVL by CLM3.0.In AGVL,the downward long-wave radiation is underestimated in spring and summer.The deviation of the model for simulating long-wave radiation downward from NSL is within±0.02.Before and after sunrise,the high albedo value of the model simulation is delayed compared with the observational measurements,and the albedo is overestimated,resulting in an overestimation of the reflected solar radiation of about 6-19 W/m².Additionally,for up-going long-wave radiation,the modelin the peak region underestimates up-going long-wave radiation,and generally with an underestimation about 2-25 W/m².The simulation accuracy of long wave radiation from NSL is higher than that of AGVL.Moreover,the net radiation is quite different between the simulated and observed values.RMSE ranges from 35 to 70 W/m².The model can simulate the net radiation difference between NSL and AGVL.7)Flux simulation validation:In desert area,the simulation ability of H model is higher than LE model,and the simulation accuracy of NSL flux is better than AGVL.That also shows the simulation mechanism of water vapor transport in desert arid area needs to be improved.Meanwhile,the model overestimates the AGVL H and underestimates the NSL H.The RMSE of the AGVL is 45.6 W/m² and that of the NSL is 25.1 W/m².Soil simulation validation:the correlation coefficient of soil temperature simulation is relatively high,more than 0.97.There is an underestimation in the high temperature area.The precision of NSL simulation for upper and middle soil temperature is higher than that of AGVL,and the precision of AGVL simulation for lower soil temperature is better than that of NSL.The RMSE in spring and summer is high,while that in autumn and winter is low.From the beginning of March in spring,RMSE shows a decreasing trend in a year,and the error in December is the smallest.Besides,the simulation of soil moisture was not good,NSL correlation coefficient is higher than AGVL,and the highest can reach 0.83.The simulation deviations of soil moisture are all positive deviations.The simulation values are higher overall,the deviation of deep soil is larger,and the deviation of NSL is higher than that of AGVL.RMSE indicates that the error of NSL is higher than that of AGVL.Because of irrigation,the simulation accuracy of AGVL contains"virtual high".