Ren et al. (2026) Opposite responses of water use efficiency and carbon use efficiency to agricultural drought during winter wheat growth period in the core area of grain production in the ancient course of Yellow River

Identification

• Journal: Agricultural Water Management
• Year: 2026
• Date: 2026-01-15
• Authors: Xiaojuan Ren, Guodong Li, Xuejian Sun, Hui He, Qingtao Zhao, Longsheng Wang, Gong Yunfei, Bo Han, Chenxi Cao
• DOI: 10.1016/j.agwat.2026.110144

Research Groups

• College of Geographical Sciences, Faculty of Geographical Science and Engineering/Key Laboratory of Geospatial Technology for the Middle and Lower Yellow River Regions, Ministry of Education, Henan University, Zhengzhou 450046, China
• Henan Dabieshan National Field Observation and Research Station of Forest Ecosystem, Henan University, Zhengzhou 450046, China
• Xinyang Academy of Ecological Research, Xinyang 464000, China

Short Summary

This study systematically evaluated the spatiotemporal variations and threshold responses of winter wheat carbon and water use efficiencies (CUE and WUE) to agricultural drought and environmental factors in the ancient course of the Yellow River. It found that CUE and WUE exhibit opposite responses to drought, with a critical drought threshold at TVDI = 0.5, which can serve as a key decision point for irrigation.

Objective

• Reveal the spatiotemporal dynamics of agricultural drought during the growth period of winter wheat in the ancient course of the Yellow River over the past 20 years.
• Clarify the interannual spatiotemporal variations of CUE and WUE during the growth period of winter wheat.
• Identify the threshold responses and regulatory mechanisms of CUE and WUE to TVDI and climate factors under drought stress, establish an irrigation early warning system based on the TVDI threshold, and optimize irrigation strategies under different drought conditions.

Study Configuration

• Spatial Scale: Winter wheat planting areas (approximately 21130 km²) within the ancient course of the Yellow River, spanning Jiangsu, Anhui, Shandong, and Henan provinces, China.
• Temporal Scale: 23-year period from 2001 to 2023, focusing on the winter wheat growing season.

Methodology and Data

• Models used:
  • Temperature Vegetation Dryness Index (TVDI) for drought assessment.
  • Water Use Efficiency (WUE) calculated as Gross Primary Productivity (GPP) / Evapotranspiration (ET).
  • Carbon Use Efficiency (CUE) calculated as Net Primary Productivity (NPP) / GPP.
  • Theil-Sen trend analysis and Mann-Kendall trend test (Sen+MK) for spatiotemporal trend analysis.
  • Hurst index (H) for future trend prediction.
  • Random Forest model and Partial Dependence Plots (PDP) for assessing factor importance and threshold responses.
• Data sources:
  • Remote Sensing: Google Earth Engine (GEE) platform for MODIS products (2001–2023):
    • MOD13A2 (16-day composite NDVI, 1 km spatial resolution).
    • MOD11A2 (8-day composite Land Surface Temperature (LST), 1 km spatial resolution).
    • MODIS/061/MOD16A2GF (8-day ET, 500 m spatial resolution).
    • MODIS/061/MOD17A2H (8-day GPP, 500 m spatial resolution).
    • MODIS/061/MOD17A3HGF (Annual NPP, processed to 8-day, 500 m spatial resolution).
  • Crop Distribution: 1 km planting distribution dataset of major grain crops in China from the National Ecological Science Data Center.
  • Climate Data: TerraClimate dataset (1958–present) for monthly climate and hydrological variables, synthesized for the winter wheat growth period:
    • Solar radiation (Srad).
    • Precipitation (Pre).
    • Average temperature (Tavg).
    • Soil moisture (SM).
    • Wind speed (WS).
    • Vapor pressure deficit (VPD).
  • Ground Validation: Eddy covariance system (LI-COR, USA) at Fengqiu Agro-Ecosystem station for GPP and ET (2018, 2019, 2023) validation (R² of 0.88 for GPP, 0.73 for ET). NPP estimated using observed GPP and a cropland ratio (φ) of 0.5399 (R² = 0.88).

Main Results

• The winter wheat growing period was predominantly characterized by mild drought (TVDI between 0.4 and 0.6), with the annual mean TVDI showing a fluctuating upward trend at a rate of 0.002 a⁻¹, indicating intensifying drought risk. Spatially, drought was more severe in the west and milder in the east.
• Over 23 years, CUE exhibited a fluctuating downward trend (linear decrease rate of −0.001 a⁻¹, mean 0.47), while WUE showed a significant upward trend (linear increase rate of 1.3 × 10⁻² kgC m⁻³ a⁻¹, mean 1.74 kgC m⁻³).
• In regions with intensified drought (2003–2023), CUE decreased in 63.9 % of the area, whereas WUE increased in 98 % of the area, demonstrating opposite responses.
• TVDI = 0.5 was identified as a critical drought threshold and a key irrigation decision point. Below this threshold, WUE increased with drought intensity while CUE decreased. Above this threshold, the trends reversed, indicating carbon-water metabolic damage.
• Wind speed (WS) was the most important environmental factor influencing both CUE (relative importance 44.75 %) and WUE (relative importance 37.85 %).
• Multi-factor synergistic analysis revealed that mild drought combined with lower hydrothermal conditions or high VPD (650–750 Pa) tended to form low-CUE zones. Conversely, mild drought combined with suitable hydrothermal conditions (e.g., precipitation around 0.25 m, soil moisture around 0.030 m, solar radiation around 162 W m⁻², or average temperature between 282.65 K and 283.65 K) optimized WUE. Severe drought consistently led to carbon-water metabolic damage.

Contributions

• Provided a systematic evaluation of spatiotemporal variations and threshold responses of winter wheat carbon-water use efficiency to agricultural drought and environmental factors in a critical grain production region.
• Identified a quantitative drought threshold (TVDI = 0.5) for irrigation initiation, offering a scientific basis for precision irrigation management.
• Elucidated the complex, opposite threshold responses of CUE and WUE to drought stress and the regulatory mechanisms under multi-factor influences.
• Proposed a three-level irrigation management system (preventive, critical, emergency) based on the TVDI-WUE-CUE coupling framework, enhancing efficient water resource utilization and ensuring crop growth.
• Contributed to understanding agricultural drought risk under climate change and optimizing regional water resource allocation strategies.

Funding

• National Natural Science Foundation of China (No.42171112)
• Key Research and Development Project in Henan Province (No. 252102321102)
• Natural Science Foundation of Henan Province (No.242300420218)
• Xinyang Academy of Ecological Research Open Foundation (No. 2023DBS04)
• ChinaFLUX

Citation

@article{Ren2026Opposite,
  author = {Ren, Xiaojuan and Li, Guodong and Sun, Xuejian and He, Hui and Zhao, Qingtao and Wang, Longsheng and Yunfei, Gong and Han, Bo and Cao, Chenxi},
  title = {Opposite responses of water use efficiency and carbon use efficiency to agricultural drought during winter wheat growth period in the core area of grain production in the ancient course of Yellow River},
  journal = {Agricultural Water Management},
  year = {2026},
  doi = {10.1016/j.agwat.2026.110144},
  url = {https://doi.org/10.1016/j.agwat.2026.110144}
}