Seasonal and Interannual Variations in the Surface Energy Fluxes of a Rice–Wheat Rotation in Eastern China

Abstract

Quantitative knowledge of the water and energy exchanges in agroecosystems is vital for irrigation management and modeling crop production. In this study, the seasonal and annual variabilities of evapotranspiration (ET) and energy exchanges were investigated under two different crop environments – flooded and aerobic soil conditions – using three years (June 2014 to May 2017) of eddy covariance observations over a rice–wheat rotation in eastern China. Across the whole rice-wheat rotation, the average daily ET rate in the rice paddies and wheat fields was 3.6 mm d–1 and 2.4 mm d–1, respectively. The average seasonal ET was 473 and 387 mm for rice and wheat fields, indicating a higher water consumption for rice than for wheat. Averaging for the three cropping seasons, rice paddies had 52% more latent heat flux than wheat fields, whereas wheat had 73% more sensible heat flux than rice paddies. This resulted in a lower Bowen ratio in the rice paddies (0.14) than in the wheat fields (0.4). As eddy covariance observations of turbulent heat fluxes are typically less than the available energy (Rn − G, i.e., net radiation minus soil heat flux), energy balance closure (EBC) therefore does not occur. For rice, EBC was greatest at the vegetative growth stages (mean: 0.90) after considering the water heat storage, whereas wheat had its best EBC at the ripening stages (mean: 0.86).

A benchmark dataset of diurnal- and seasonal-scale radiation, heat and CO<sub>2</sub> fluxes in a typical East Asian monsoon region

“…Although the sites are in the same climate monsoon area, large differences existed in λE and H over different surface types. Seasonal variations in λE at the two cropland sites had doublet peaks, which were closely related to the crop phenology and agricultural activities (Duan et al, 2021a). For example, daily mean λE firstly increased from 3 W m −2 (5 W m −2 ) in January to a peak value of 110 W m −2 (182 W m −2 ) in April and then gradually decreased when wheat was harvested at the SX-cropland site (DT-cropland site).…”

“…The soil at the site is predominantly clay. The site is homogeneous, and a rotation of summer rice and winter wheat is cultivated in the field (Li et al, 2017;Duan et al, 2021a). Here, winter wheat grows from December to May, whereas summer rice grows from June to November every year.…”

“…In addition, the seasonal variations in K ↓ received at the surface were also greatly affected by weather and cloud conditions (X. Duan et al, 2021a). For instance, the highest daily mean K ↓ was 317 W m −2 for the SX-cropland site, 329 W m −2 for the DT-cropland site, and 336 W m −2 for the DS-suburb site in May 2016, and it was 332 W m −2 for the XZ-suburb site in June 2016 (Fig.…”

“…Over the past few years, some atmospheric field experiments have been conducted over various land surface types, such as croplands (Ge et al, 2018;Dai et al, 2019;Duan et al, 2021a) and urban areas (Ao et al, 2016;Wei et al, 2020), in order to examine the temporal and spatial characteristics of the energy balance and greenhouse gases in the YRD. Nevertheless, integrated measurements from field stations in the YRD are still either not openly shared or only very limited data during a specified observation period can be accessed.…”

Change of Rice Paddy and Its Impact on Human Well-Being from the Perspective of Land Surface Temperature in the Northeastern Sanjiang Plain of China

“…When paddy fields invaded adjacent land use types such as the upland crop region, the waterless environment of upland crops was replaced by the flooded environment of paddy fields, bringing about a change in the balance of surface radiation energy, such as the reduced sensible heat flux and increased latent heat flux [ 27 ]. Such energy change may bring comfort to the living environment in agricultural planting regions in hot summer, considering the evaporation and transpiration from the large-scale paddy fields [ 28 , 29 ]. The land surface temperature was a direct indicator reflecting human well-being [ 30 ].…”