Simulation Study On The Impact Of Large Area Plastic Mulch Cover On Regional Climate In Arid Area

In arid areas,in order to increase agricultural production,the plastic mulch covering is usually used to suppress water evaporation in soil and improve water use.In terms of land-atmosphere interaction,large area plastic mulch-cover significantly changes the land surface parameters,and prevents vapour exchange between the land surface and the atmosphere.These changes could affect the land surface process,and then impacts on the regional climate.In this paper,the Gulang Heterogeneous Underlying Surface Layer Experiment(GHUSLE),the observation data under the condition of plastic mulch covering in northwest China,and the NOAH LSM land surface model(referred to as NOAH)and the WRF regional climate model were used to simulate the effects of plastic mulch cover to land surface model and regional climate model.The results showed as following:Firstly,the land surface process characteristics of the plastic mulch cover surface of field in the GHUSLE experiment were analyzed,and the simulation performance of the NOAH model on the special underlying surface was examined.The results indicated that the hydrothermal transmission characteristics of the underlying surface of the plastic mulch covering area are arid in the shallow layer,which is influenced by the solar radiation and has a significant diurnal variation.However,the changes in deep layer is weak.The four components of the radiation show a single peak-type,the surface comprehensive albedos indicate U-shaped,the impacts of plastic mulch cover on the upward shortwave radiation is also pronounced.The surface comprehensive albedo is higher before observation than after.The energy balance of farmland stations is dominated by latent heat flux,which is mainly associated to vegetation transpiration.The numerical simulation showed that all the land surface characteristic variables from NOAH model have large deviation compared to the observed values,which indicates that NOAH model can not reasonably characterize the land surface process characteristics of this special underlying surface.Secondly,considering the effect of plastic mulch cover on surface comprehensive albedo and evaporation,the Particle Swarm Optimization(PSO)algorithm is used to optimize the land surface parameters in NOAH mode,and formed a NOAH_MULCH mode suitable for the underlying surface of the plastic mulch covering.According to the comparison with the observed data,it is found that NOAH_MULCH model significantly improves the simulation ability of the land surface process characteristics of the underlying surface of the plastic mulch cover,and the simulated upward short wave,upward long wave,sensible heat and latent heat flux are closer to the observed value.Compared with the original NOAH model,it was found that the plastic mulch cover significantly affected the radiation balance,turbulent flux and soil temperature and humidity.Finally,the NOAH_MULCH mode is coupled into the WRF model to simulate the effect of large area plastic mulch covering on regional climate.By comparing the characteristics of meteorological elements and land surface processes with or without plastic mulch covering,the following conclusions are obtained:After covering a large area of plastic mulch,soil moisture increased by 0.009-0.090m3 m-3;soil temperature decreased 0.2-1.6K;the latent heat flux is reduced by 2-15W·m-2;the sensible heat flux reduced by 10-45W·m-2;the net radiation flux is increased by 12-23.W·m-2.;the surface specific humidity decreased,the maximum reached 0.16g/kg;the surface temperature decreased,the maximum reached 1.6K;the surface pressure rise,the maximum reached 11Pa.These results indicated that a large number of plastic mulch covering can affect the meteorological elements and land surface characteristics at the regional-scale.