Jin et al. (2025) Surface energy balance under paddy-upland rotation in the lakeside area of Erhai Lake, Southwest China

Identification

• Journal: Theoretical and Applied Climatology
• Year: 2025
• Date: 2025-12-01
• Authors: Lili Jin, Anlun Xu
• DOI: 10.1007/s00704-025-05927-9

Research Groups

• Department of Atmospheric Sciences, Yunnan University, Kunming, China
• Research Center for Disastrous Weather over Hengduan Mountains & Low-Latitude Plateau, China Meteorological Administration, Kunming, China
• Dali National Climate Observatory, Dali Field Research Station for Mountain Meteorology, China Meteorological Administration, Dali, China
• Dali Mountain Meteorology Observation and Research Station of Yunnan Province, Dali, China

Short Summary

This study investigated surface energy balance (SEB) characteristics and compared Large Aperture Scintillometer (LAS) and Eddy Covariance (EC) systems in a paddy-upland rotation area near Erhai Lake, Southwest China, revealing crop- and atmospheric stratification-dependent advantages of LAS in improving sensible heat flux quantification and overall energy balance closure.

Objective

• Analyze the surface energy components and their balance characteristics over a two-year period (2014–2015) in a seasonal rice-fava bean rotation system in the Dali area.
• Verify whether the Large Aperture Scintillometer (LAS)-derived sensible heat flux (HLAS) contributes to improved energy balance closure compared with Eddy Covariance (EC)-derived sensible heat flux (HEC) under varying crop rotation phases.

Study Configuration

• Spatial Scale: Farmland underlying surface in Dali, Erhai Lake lakeside, Southwest China (25°42′ N, 100°11′ E, altitude 1977.7 m). The 90% flux footprint area was approximately 0.1118 km². The LAS path length was 1.938 km, with the EC system 224 m from the LAS receiver. Soil bulk density measurements were 1140 kg/m³, 1150 kg/m³, 1440 kg/m³, and 1380 kg/m³ at 0–10 cm, 10–20 cm, 20–30 cm, and 30–40 cm depths, respectively.
• Temporal Scale: Two-year observation period from January 2014 to December 2015, covering dry season (November to April, fava bean cultivation) and wet season (May to October, rice cultivation), as well as transition periods.

Methodology and Data

• Models used:
  • Flux Footprint Prediction (FFP) model (Kljun et al., 2015) for footprint analysis.
  • Monin-Obukhov Similarity Theory for deriving sensible heat flux from the temperature structure parameter (CT²).
  • Bowen ratio coefficient for CT² calculation.
  • Eddypro 6.2.1 for Eddy Covariance (EC) data preprocessing.
• Data sources:
  • Observation systems: Eddy Covariance (EC) system (on a 20-m tower, EC system at 5.08 m height, 20 Hz sampling) and Large Aperture Scintillometer (LAS) system (10 m effective height, 2 Hz sampling).
  • EC instruments: Three-dimensional ultrasonic anemometer, MET ONE 034B wind sensors (at 2 m, 4 m, 10 m, 20 m), CNR1 net radiometer (Kipp and Zonen), soil temperature and moisture sensors (at 4 cm, 10 cm, 20 cm, 60 cm, 100 cm depths), soil heat flux plates (at 4 cm, 10 cm, 20 cm).
  • Data loggers: CR3000.
  • Measured variables: Net radiation (Rnet), sensible heat flux (H), latent heat flux (LE), soil heat flux (G0), air temperature, wind speed, specific humidity, soil temperature, soil moisture, precipitation, albedo, and cloud cover.

Main Results

• Albedo and Radiation: Surface albedo was highest during the fava bean period (0.22), leading to lower net shortwave radiation (163 W/m²) compared to the rice period (0.16 albedo, 181 W/m² net shortwave radiation). Net shortwave radiation was the dominant energy input (77% to 91% of Rnet).
• Evaporation: Rice fields exhibited the highest daily evaporation (3.72 mm water equivalent), driven by latent heat flux, which was the major energy output (10% to 51% of Rnet).
• Cloud Effects: The weakening effect of clouds on incident solar radiation (12.5% decrease) was less pronounced than their enhancing effect on longwave radiation (14.2% increase). Latent heat flux over rice fields showed greater sensitivity to cloud cover.
• Sensible Heat Flux (H) Comparison:
  • HLAS exceeded HEC by 20.9 W/m² during the fava bean period and 14.1 W/m² during the transition period.
  • Under stable atmospheric stratification, HLAS was significantly higher than HEC (51% higher in dry season, 82% higher in wet season), indicating LAS's ability to capture large-scale turbulence.
  • EC underestimated sensible heat flux, particularly under stable conditions.
  • During wet-season daytime unstable conditions, HLAS lagged EC, showing a negative difference (HLAS − H_EC = −24.9 W/m²).
• Soil Moisture Impact: Energy components during the fava bean period responded to soil moisture levels ≥ 0.2 m³/m³, while those during the rice period responded to levels < 0.4 m³/m³. Soil heat flux (G0) in fava bean fields peaked with soil moisture between 0.4 and 0.5 m³/m³, whereas in rice fields, it peaked at soil moisture content ≤ 0.1 m³/m³.
• Vertical Heat Transfer Coefficient (Rwt): Optimal agreement between HLAS and HEC (ratio ≈ 1) was observed when Rwt ranged from 0.4 to 0.5.

Contributions

• Provides novel insights into surface energy balance dynamics under low-latitude plateau monsoon conditions in a paddy-upland rotation system.
• Quantifies the crop- and atmospheric stratification-dependent advantages of Large Aperture Scintillometer (LAS) in enhancing sensible heat flux quantification and improving energy balance closure compared to Eddy Covariance (EC).
• Offers a methodological reference for energy balance research in heterogeneous agricultural landscapes.
• Delivers practical recommendations for agricultural and environmental monitoring, suggesting LAS for dry season fava bean fields and EC for wet season rice fields during daytime in lake-farmland transitional zones.
• Establishes a vertical heat transfer coefficient (Rwt) threshold (0.4–0.5) as a quick indicator for flux data reliability, aiding in data quality control.
• Contributes to improving land surface models by elucidating moisture- and cloud-driven flux discrepancies.

Funding

• Yunnan Province "Xingdian Talent Support Plan" young talent special
• National Natural Science Foundation of China (42275163)
• Innovation and Development Project of China Meteorological Administration (CXFZ2025J147)

Citation

@article{Jin2025Surface,
  author = {Jin, Lili and Xu, Anlun},
  title = {Surface energy balance under paddy-upland rotation in the lakeside area of Erhai Lake, Southwest China},
  journal = {Theoretical and Applied Climatology},
  year = {2025},
  doi = {10.1007/s00704-025-05927-9},
  url = {https://doi.org/10.1007/s00704-025-05927-9}
}