Abstract
Plastic film mulch, which effectively maintains soil moisture by suppressing soil evaporation, has been widely used in cropland in Northwest China, where water scarcity severely restricts agricultural development. Plastic mulch affects surface albedo and blocks water vapor exchange between soil and atmosphere. Therefore, the large area of cropland covered by plastic film will have serious impacts on regional climate by modifying the surface-atmosphere partitioning of vapor and energy. In this study, a dynamic irrigation scheme was incorporated into the Weather Research and Forecasting model with Noah land surface scheme; two experiments (with and without plastic mulch) were designed to simulate the impacts of plastic mulch over cropland in Northwest China on regional climate. In irrigated cropland, the irrigation amount decreased substantially during the early stage of crop growth (ESCG; from 22 April to 1 July) with plastic mulch, especially in May, indicating that plastic mulch conserved agricultural water. In nonirrigated cropland, soil moisture in cropland with plastic mulch was clearly greater than that without plastic mulch. The influences of plastic mulch on land surface processes were mainly reflected in the ESCG, such that upward shortwave radiation increased and latent heat flux decreased. In cropland during the ESCG, after plastic mulch, the latent heat flux decreased significantly by 12–30 W m−2, the sensible heat flux increased significantly by 8–16 W m−2, and the surface air temperature increased significantly by 0.2–0.8 °C. The plastic mulch reduced water vapor in the lower atmosphere, which might lead to decrease precipitation in Northwest China.
Highlights
Oasis cropland, an active component of ecosystems in the extensive arid and semi-arid regions of Northwest China, links the underlying surface and atmosphere by modulating the exchanges of energy and mass across the interfaceIn the irrigated cropland of Northwest China, the scarcity of precipitation inevitably leads to the use of large amounts of irrigation water, but water resources are very scarce here; saving agricultural water is very important and meaningful
The physical processes parameterization schemes were selected for the simulation experiments as follows: the Weather Research and Forecasting (WRF) singlemoment six-class (WSM6) graupel microphysics scheme (Hong and Lim 2006), the Rapid Radiative Transfer Model (RRTM) longwave radiation (Mlawer et al 1997), Dudhia shortwave radiation (Dudhia 1989), the Yonsei University (YSU) planetary boundary layer scheme (Hong et al 2006), the new Kain-Fritsch cumulus scheme (Kain 2004), and the Noah land surface model (Chen and Dudhia 2001)
This study mainly focused on the effects of plastic film mulch, but snow had great influences on surface albedo, and some cropland might be covered by snow in April, especially in northern Xinjiang
Summary
An active component of ecosystems in the extensive arid and semi-arid regions of Northwest China, links the underlying surface and atmosphere by modulating the exchanges of energy and mass across the interfaceIn the irrigated cropland of Northwest China, the scarcity of precipitation inevitably leads to the use of large amounts of irrigation water, but water resources are very scarce here; saving agricultural water is very important and meaningful. Plastic film mulch can effectively inhibit soil evaporation and maintain soil moisture (Liu et al 2009; Wang et al 2009; Yang et al 2012; Cuello et al 2015; Yuan et al 2019), which saves irrigation water, indicating that plastic film mulch technology has high potential for application in the cropland of Northwest China. This technology has been widely used in some irrigated cropland and its area of use is expected to continue to grow. In cropland covered with plastic film, experiments considering the plastic mulch scheme showed obvious improvement in simulating several variables such as vapor and energy, indicating that the physical processes of plastic mulch should be implemented into the land surface models for studying vapor and energy in cropland ecosystems with plastic mulch
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