Gaoyuan qixiang (Jun 2023)
Simulation of Land-Atmosphere Water and Heat Exchange over the Underlying Surface of Different Crops on the Loess Plateau
Abstract
Changes in the planting structure of farmland on the Loess Plateau impact land surface energy and water exchange， regional evapotranspiration， etc.The complex hydrothermal coupling mechanism of different crop underlying surfaces plays an essential role in the land-atmosphere interaction on the Loess Plateau.In this paper， based on the observation data of 34 months from 2019 to 2021 in the east of Gansu province， combined with CLM5.0-BGCCROP coupled with the crop module， the land surface characteristics of different typical crops （winter wheat， corn， and apple forest） on the Loess Plateau were offline single-point simulated.To verify the simulation ability of CLM5.0 on the land surface processes of agricultural fields on the Loess Plateau and compare the differences in soil temperature， soil liquid water content， and surface energy fluxes of different crops.The results showed that： （1） CLM5.0 has a better simulation effect on soil temperature and liquid water content characteristics， average RMSE is less than 2.5℃ and 0.1 m3·m-3， respectively.The simulated soil temperature values in the wheat field are high， and there is a cold bias in the corn and apple fields.Winter wheat， which has a dry growth period， caused more soil drying than corn.Apple forest， which has a rich root system， absorbed more soil water， making the soil drier overall.（2） Part of the simulation bias is due to setting crop underlying surfaces to a single crop functional type in the model， overestimating the leaf area index of crops during the growth period， underestimating the surface albedo， overestimating the net radiation flux， and converting more energy flux into sensible and latent heat flux.（3） Another part of the simulation bias comes from the diverse crop management methods in the farmland.For example， crop fields are not completely tilled to bare soil after harvest， and the model overestimates soil temperature and soil liquid water content in wheat and corn fields.The model does not have the mulching option， which leads to the low simulated soil temperature and soil liquid water content in corn fields， about 1.84℃ and 0.058 m3·m-3， respectively.（4） The winter wheat and corn mixed crop underlying surface simulation experiment could better simulate the surface energy fluxes， and the simulated average deviations of net radiation， sensible heat flux， and latent heat flux were -6.13 W·m-2， 11.46 W·m-2， -1.97 W·m-2， respectively.During the growth period， canopy transpiration dominates， and with the increase of crop leaf area index， sensible heat flux decreases， soil temperature decreases， latent heat flux increases， and soil liquid water content decreases.
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