Improvement and Validation of the Common Land Model on Cropland Covered by Plastic Film in the Arid Region of China

Abstract

AbstractPlastic mulch is a technology used worldwide to inhibit soil evaporation and increase crop yield. The properties of plastic film are significantly different from those of the soil. Plastic mulch not only significantly alters the physical attributes of the underlying surface, but also blocks the energy and mass exchanges between the land surface and the atmosphere. This latter situation has not been depicted in current land-surface models. This study develops a detailed new model, known as CoLM-mulch, by incorporating a plastic mulch–layer submodel and a dynamic parameterization scheme of surface albedo into the Common Land Model (CoLM) land-surface process model. The updated model elements are based on data collected from an experiment that examined land–atmosphere interaction at a plastic-film-covered cropland site in an arid region of northwestern China. Results suggest that the improved CoLM-mulch could reasonably simulate the diurnal variations of soil temperature and moisture, together with radiation, water, heat, and carbon dioxide (CO2) fluxes, on the cropland underlying a surface with a plastic film covering. The CoLM-mulch efficiency is higher, the deviations between the simulations and observations are minor, and the dynamic parameterization scheme for surface albedo is more reasonable and appropriate. Relative to CoLM simulations, the inclusion of plastic mulch with special optical properties in the model shows slight improvements in the simulations of the surface albedo and the radiation balance. By limiting the underlying soil evaporation and changing the aerodynamic resistances, plastic mulch in the model has influences on the turbulent exchanges between the atmosphere and the land surface. The soil temperature and moisture are improved by the inclusion of transparent plastic mulch in the model, which not only suppresses the CO2 generated by soil respiration, but also alters the CO2 exchange process between the canopy and the atmosphere as a result of the vegetation net assimilation controlled by the soil water and heat conditions.