Zhu et al. (2026) Evaluation of the accuracy and response to recorded irrigation events of remote sensing and reanalysis soil moisture products in a typical irrigation district

Identification

• Journal: Agricultural Water Management
• Year: 2026
• Date: 2026-09-28
• Authors: Rui Zhu, Yu Li, Jiawei Lv, Lei Wang, Zhiqing Cheng, Dong Wu
• DOI: 10.1016/j.agwat.2026.110822

Research Groups

• College of Resources and Environment, Anhui Agricultural University, Hefei, Anhui, China
• National Climate Center, China Meteorological Administration, Beijing, China

Short Summary

This study comprehensively evaluated the accuracy and irrigation-associated response characteristics of seven microwave and reanalysis soil moisture products in the North China Plain using two in situ observation networks. It found that product suitability depends on the monitoring objective, with ERA5-Land performing best for continuous monitoring and ESA CCI Passive showing greater sensitivity to short-term irrigation-associated wetting.

Objective

• To assess the accuracy of different surface and root-zone soil moisture products in a typical irrigation district.
• To evaluate how these soil moisture products respond to recorded irrigation events under precipitation-controlled conditions.

Study Configuration

• Spatial Scale: North China Plain (NCP), approximately 4 × 10^5 km^2, covering parts of five provinces and two municipalities in eastern China.
• Temporal Scale: September 2015 to November 2021 (varying by dataset).

Methodology and Data

• Models used: GLDAS-Noah (V2.1), ERA5-Land (V2), SMAP-L4 (V6) (model-based assimilation product).
• Data sources:
  • In situ observations: Automatic Meteorological Station network (AMS, 733 stations, daily volumetric water content at 10 depths down to 1 m from September 2015 to October 2021); Agro-Meteorological Experimental Station network (AES, 30 stations, gravimetric soil moisture by oven-drying method on 8th, 18th, 28th of each month, 0–100 cm profile at 10 cm intervals, February 2017 to November 2021, including detailed irrigation records).
  • Satellite retrieval products: ESA CCI Combined (V6.1), ESA CCI Passive (V6.1), ESA CCI Active (V6.1), ASCAT H115 (12.5 km, daily).
  • Reanalysis products: ERA5-Land (0.1°, hourly), GLDAS-Noah (0.25°, 3-hourly).
  • Auxiliary data: Soil bulk density (from AES and Land–Atmosphere Interaction Research Group at Sun Yat-sen University), daily precipitation data (National Meteorological Science Data Center, ERA5-Land, GLDAS-Noah).

Main Results

• Overall Accuracy: AES-based evaluations generally showed higher overall correlation (R = 0.58) and smaller errors with SM products than AMS-based evaluations (R = 0.54). However, on common observation dates, AES-based correlations decreased, while biases approached zero.
• Continuous Monitoring: ERA5-Land consistently performed best for continuous soil moisture monitoring, showing the highest correlation (R = 0.54 for AMS, R = 0.58 for AES) and lowest errors across both networks and growing seasons.
• Irrigation Response:
  • On recorded irrigation days, ESA CCI Passive achieved the highest correlation (R = 0.69) and the lowest unbiased root mean square error (ubRMSE = 0.043 m^3 m^-3) with AES observations.
  • Under strict precipitation-controlled conditions, satellite-observation-constrained products (especially ESA CCI Passive) exhibited more pronounced positive soil moisture response amplitudes (ΔSM) compared to ERA5-Land and GLDAS-Noah, indicating greater sensitivity to short-term irrigation-associated wetting.
  • ERA5-Land and GLDAS-Noah showed little systematic positive change when precipitation was controlled, with median ΔSM values near or below zero.
• Threshold Sensitivity: The probability of detection (POD) for irrigation events varied substantially with the selected ΔSM response threshold, highlighting the need for explicit threshold-sensitivity analysis. ERA5-Land and GLDAS-Noah yielded POD values of zero across the evaluated threshold range.

Contributions

• Provides a comprehensive, multi-network evaluation of remote sensing and reanalysis soil moisture products in a typical irrigation district, addressing a gap in applicability assessment.
• Differentiates product suitability based on monitoring objectives: ERA5-Land for continuous monitoring and ESA CCI Passive for short-term irrigation-associated wetting.
• Emphasizes the critical importance of multi-source precipitation screening and threshold-sensitivity analysis for robust interpretation of irrigation-associated soil moisture responses.
• Highlights the complementary nature of different ground observation networks (AMS for continuous data, AES for irrigation-specific validation) in complex agricultural environments.

Funding

• Anhui Provincial Natural Science Foundation (grant number 2208085QD120)
• Talent Funding of Anhui Agricultural University (grant number rc522111)

Citation

@article{Zhu2026Evaluation,
  author = {Zhu, Rui and Li, Yu and Lv, Jiawei and Wang, Lei and Cheng, Zhiqing and Wu, Dong},
  title = {Evaluation of the accuracy and response to recorded irrigation events of remote sensing and reanalysis soil moisture products in a typical irrigation district},
  journal = {Agricultural Water Management},
  year = {2026},
  doi = {10.1016/j.agwat.2026.110822},
  url = {https://doi.org/10.1016/j.agwat.2026.110822}
}