Hornero et al. (2026) Assessing CWSI as an indicator of water stress in oak trees based on high-resolution thermal images

Identification

• Journal: Remote Sensing of Environment
• Year: 2026
• Date: 2026-06-28
• Authors: A. Hornero, J.L. Quero, Zarco-Tejada P. J, Victoria Gonzalez-Dugo, Francisco Tomás-Riera, M.J. Marcos, R. Hernandez-Clemente
• DOI: 10.1016/j.rse.2026.115549

Research Groups

• Instituto de Agricultura Sostenible (IAS), Consejo Superior de Investigaciones Científicas (CSIC)
• Faculty of Engineering and Information Technology (FEIT), The University of Melbourne
• Departamento de Ingeniería Forestal, Universidad de C´ordoba
• Department of Geography, Swansea University

Short Summary

This study explores the use of the Crop Water Stress Index (CWSI) as an indicator of water stress in holm oak (Quercus ilex) forests using high-resolution thermal images. The results show that the CWSI is significantly correlated with both stem water potential and stomatal conductance, suggesting its reliability for monitoring water status in oak trees.

Objective

• To determine whether the Crop Water Stress Index (CWSI) is a suitable index for oak trees
• To evaluate the utility of the CWSI for detecting water stress in declining Mediterranean oak trees using high-resolution thermal imaging

Study Configuration

• Spatial Scale: Local to regional scale, with two study areas located in Andalusia, Spain
• Temporal Scale: Long-term monitoring (2012–2024) with multiple flights conducted between 11 h and 14 h during the summer months

Methodology and Data

• Models used: None specified
• Data sources:
  • High-resolution thermal images collected using a FLIR SC655 camera installed onboard a Cessna aircraft
  • Field measurements of stem water potential, stomatal conductance, and crown temperature
  • Airborne campaigns with sixteenth flights conducted between 11 h and 14 h during the summer months

Main Results

• The diurnal behaviour of canopy temperature differed according to severity level and day of the year
• A significant correlation was found between stomatal conductance and water potential for affected trees (R=0.606, p-value<0.05) and for non-affected trees (R=0.533, p-value<0.05)
• The NWSB established provides a reference for assessing tree water status, where deviations from this baseline may indicate the onset of water stress
• Thermal aerial survey data from 2012 to 2024 revealed that values from all flights recorded fell within the established NWSB range

Contributions

• This study contributes to the development of a reliable indicator of water stress in oak trees using high-resolution thermal images and the Crop Water Stress Index (CWSI)
• The results provide new insights into the hydraulic functioning of oak species, particularly in the context of increasing drought events

Funding

• Not specified

Citation

@article{Hornero2026Assessing,
  author = {Hornero, A. and Quero, J.L. and J, Zarco-Tejada P. and Gonzalez-Dugo, Victoria and Tomás-Riera, Francisco and Marcos, M.J. and Hernandez-Clemente, R.},
  title = {Assessing CWSI as an indicator of water stress in oak trees based on high-resolution thermal images},
  journal = {Remote Sensing of Environment},
  year = {2026},
  doi = {10.1016/j.rse.2026.115549},
  url = {https://doi.org/10.1016/j.rse.2026.115549}
}