Zoratipour et al. (2025) Deriving hourly and daily crop water stress index through the lens of proximal sensing in sugarcane fields

Identification

• Journal: Ain Shams Engineering Journal
• Year: 2025
• Date: 2025-12-02
• Authors: Elahe Zoratipour, Shadman Veysi, Amir Soltani Mohammadi, Saeed Boroomand Nasab, Abd Ali Naseri
• DOI: 10.1016/j.asej.2025.103903

Research Groups

• Irrigation and Drainage Department, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran
• Soil and Water Research Institute (SWRI), Alborz, Iran

Short Summary

This study evaluated proximal sensing for hourly and daily Crop Water Stress Index (CWSI) detection in sugarcane fields in an arid region, identifying solar radiation and wind speed as key hourly drivers and soil moisture as a primary daily influence. It proposes a CWSI threshold of 0.4–0.5 for initiating irrigation to optimize water management.

Objective

• To quantify the hourly and daily CWSI using a stationary proximal sensing system and to diagnose the underlying environmental causes of its variation.
• To establish the critical range of CWSI for sugarcane and determine the optimal time of day for crop monitoring.
• To analyze the trend of CWSI dynamics between irrigation events.
• To determine a CWSI threshold for triggering irrigation to improve scheduling efficiency in sugarcane fields.

Study Configuration

• Spatial Scale: Four sugarcane fields, each 25 hectares, within the Amir Kabir Agro Industry Unit (total 14,000 hectares) in Khuzestan, Iran. Soil samples were collected at 0–30 cm, 30–60 cm, and 60–90 cm depths.
• Temporal Scale: Data collected from July to September 2023. Hourly measurements were taken between 6:00 and 18:00 daily, over a 9-day irrigation interval.

Methodology and Data

• Models used:
  • Crop Water Stress Index (CWSI) calculation based on Idso et al. (1981) using canopy-air temperature difference, lower limit (well-transpiring crop), and upper limit (low-transpiring crop).
  • Equations for saturated vapor pressure, actual vapor pressure, vapor pressure deficit (VPD), and vapor pressure gradient (VPG).
  • Pearson correlation coefficient (r) for assessing relationships between variables.
  • Two-factor and one-way Analysis of Variance (ANOVA) for statistical significance.
  • Tukey’s Honest Significant Difference (HSD) test for post-hoc mean comparisons.
• Data sources:
  • Proximal sensing: Stationary Apogee SI-1H1 Infrared Radiometers (IRTs) for canopy temperature (Tc), air temperature probes, and relative humidity sensors, logged by CR1000X data loggers.
  • Reanalysis data: ERA5-Land (European Centre for Medium-Range Weather Forecasts - ECMWF) for hourly solar radiation (SR) and wind speed at 10 meters (U2, converted to 2 meters height).
  • In-situ soil measurements: Mass method for soil moisture content, hydrometric approach for soil texture, and pressure plates for saturated water content (θs), field capacity (θVFC), and permanent wilting point (θVPWP).
  • GPS technology for geographic coordinates.

Main Results

• Hourly CWSI showed critical stress periods between 10:00 and 15:00. CWSI increased from 6:00 to 10:00, decreased between 10:00 and 12:00, then increased again until 14:00, and gradually eased until 18:00.
• Hourly CWSI variation was primarily controlled by solar radiation in the mornings and wind speed (U2) in the afternoons, with peak wind speeds (≥ 3.75 meters per second) occurring around 14:00.
• The CWSI value around noon (11:00–12:00) was found to be representative of the daily average stress level.
• Daily CWSI was minimized two days post-irrigation (average 0.27), corresponding to soil moisture levels near field capacity (0.30).
• Daily CWSI fluctuated between 0.16 and 0.52 from July to September. The maximum daily CWSI (0.27–0.66) occurred nine days after irrigation, with an average of 0.5 on that day.
• A CWSI threshold of 0.5 is proposed for triggering irrigation in sugarcane fields under similar arid conditions.
• Soil moisture at 0–30 cm and 0–90 cm depths showed the highest negative correlation with CWSI (−0.64 and −0.66, respectively).
• A distinct time lag was observed, with CWSI declines typically preceding a decrease in soil moisture (0–90 cm) by 1–2 days (cross-correlation coefficients ranging from −0.452 to −0.808).
• Statistical analysis confirmed that the day after irrigation (DAI) had a highly significant effect on mean CWSI (p < 0.001), and crop age also had a significant effect (p = 0.038). DAI 5 was identified as a critical hydrological and physiological threshold.

Contributions

• Provides a high-resolution, automated framework for monitoring hourly and daily CWSI in sugarcane using proximal sensing, specifically calibrated for local conditions.
• Identifies and quantifies the distinct diurnal patterns of water stress in sugarcane and attributes their primary environmental drivers (solar radiation and wind speed).
• Establishes an optimal time window (around noon) for CWSI monitoring that represents the daily average stress.
• Proposes a data-driven CWSI threshold of 0.5 for initiating irrigation, offering a practical tool for precision irrigation scheduling in water-scarce regions.
• Demonstrates the predictive capability of CWSI, showing that canopy stress can be detected 1–2 days before significant soil moisture depletion, providing a valuable lead time for proactive water management.
• Highlights the importance of locally-derived, crop-specific baselines for accurate CWSI calculation, acknowledging the methodological origin while adapting it to unique microclimates and crop physiology.

Funding

The Research Council of Shahid Chamran University of Ahvaz and the Amir Kabir Sugarcane Agro-Industry.

Citation

@article{Zoratipour2025Deriving,
  author = {Zoratipour, Elahe and Veysi, Shadman and Mohammadi, Amir Soltani and Nasab, Saeed Boroomand and Naseri, Abd Ali},
  title = {Deriving hourly and daily crop water stress index through the lens of proximal sensing in sugarcane fields},
  journal = {Ain Shams Engineering Journal},
  year = {2025},
  doi = {10.1016/j.asej.2025.103903},
  url = {https://doi.org/10.1016/j.asej.2025.103903}
}