Zhu et al. (2026) Evaluating the impact of elevated CO2 on the hydrological cycle and carbon budgets in the loess plateau

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2026
• Date: 2026-01-05
• Authors: Bowen Zhu, Xianhong Xie, Yi Yao, Xuehua Zhao
• DOI: 10.1016/j.ejrh.2026.103104

Research Groups

• College of Water Resource Science and Engineering, Taiyuan University of Technology, Taiyuan, China
• State Key Laboratory of Remote Sensing, Faculty of Geographical Science, Beijing Normal University, Beijing, China
• Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland

Short Summary

This study employs the Community Land Model (CLM5) to evaluate the impact of elevated CO₂ (eCO₂) on water-carbon interactions across diverse land cover types in China's Loess Plateau, revealing that eCO₂ enhances gross primary productivity and water use efficiency while altering hydrological partitioning, with significant spatial heterogeneity in responses.

Objective

• To assess the ability of CLM5 to simulate regional ecohydrological dynamics in the Loess Plateau.
• To quantify the historical impact of rising CO₂ levels on hydrological partitioning and carbon uptake.
• To examine variations in ecosystem water use efficiency (WUE) across natural and managed landscapes.

Study Configuration

• Spatial Scale: Loess Plateau (LP), China (approximately 640,000 km²), at a model resolution of 0.0625°.
• Temporal Scale: Historical simulation from 2000 to 2023, following a 100-year spin-up period.

Methodology and Data

• Models used: Community Land Model version 5 (CLM5).
• Data sources:
  • Forcing data: Interpolated ground-based observations from 2481 meteorological stations in China (precipitation, wind speed, air temperature, radiation, relative humidity).
  • Land cover: Landsat Thematic Mapper (TM) images (1 km resolution) and 500-m MODIS-based maps for crop types.
  • CO₂ concentration: National Oceanic and Atmospheric Administration (NOAA) Open Data Dissemination Program Datasets.
  • Agricultural management: Annual maps of China's irrigated cropland (2000-2020) and historical nitrogen fertilizer data.
  • Validation data: In situ observations from two ChinaFLUX eddy covariance flux tower sites (Xiaolangdi and Qingyang) for water, energy, and carbon fluxes; Moderate Resolution Imaging Spectroradiometer (MODIS) products (GPP, ET, LAI, skin temperature).

Main Results

• Elevated CO₂ (eCO₂) nearly doubled gross primary productivity (GPP) by 2.78 gC/m²/yr across the Loess Plateau.
• Evapotranspiration (ET) was suppressed by 1.42 mm/yr, while baseflow increased by 1.09 mm/yr across the Loess Plateau due to eCO₂.
• Vegetation carbon (TOTVEGC) showed significant gains of approximately 19.16 gC/m²/yr under dynamic CO₂, whereas soil organic carbon (TOTSOMC) continued to decline at 6.01 gC/m²/yr.
• Water use efficiency (WUE) improved disproportionately across land types: forests exhibited a 50% increase, grasslands showed moderate improvements, and croplands displayed only a 10% improvement, likely constrained by irrigation.
• The marginal gain in WUE per unit increase in CO₂ (WUE/CO₂ ratio) declined by 14% from 2000 to 2023, indicating diminishing returns.
• Surface runoff differences between dynamic and constant CO₂ scenarios were minimal across all land types, ranging from -0.007 to -0.019 mm/yr.

Contributions

• Advances land surface modeling by employing CLM5 at a high spatial resolution with detailed land cover classifications, addressing the oversimplification of land cover heterogeneity in existing models.
• Provides a quantitative assessment of the historical impact of rising CO₂ on coupled water-carbon cycles in the Loess Plateau, establishing empirical linkages between observed CO₂ increases and ecosystem responses.
• Highlights the critical role of spatial heterogeneity and land-cover-specific responses (forests, grasslands, croplands) in modulating CO₂ effects on hydrological partitioning and carbon uptake.
• Reveals that anthropogenic management practices (e.g., irrigation) in croplands can significantly dampen CO₂-driven water use efficiency benefits, a nuance often overlooked.
• Offers actionable insights for climate adaptation strategies and ecological restoration, suggesting that afforestation in specific zones can maximize CO₂-driven water and carbon co-benefits.

Funding

• National Natural Science Foundation of China (42301033, 42271021, and 52279020).

Citation

@article{Zhu2026Evaluating,
  author = {Zhu, Bowen and Xie, Xianhong and Yao, Yi and Zhao, Xuehua},
  title = {Evaluating the impact of elevated CO2 on the hydrological cycle and carbon budgets in the loess plateau},
  journal = {Journal of Hydrology Regional Studies},
  year = {2026},
  doi = {10.1016/j.ejrh.2026.103104},
  url = {https://doi.org/10.1016/j.ejrh.2026.103104}
}