Investigating Temporal and Spatial Changes in Potential Evapotranspiration in East Azerbaijan Province Using MODIS Sensor Images

Background and Objectives
Potential evapotranspiration (PET) serves as a critical indicator of water balance and environmental health, prominently impacting agricultural productivity, water resource management, and ecological sustainability. In arid and semi-arid regions like East Azerbaijan province, understanding PET variations is crucial for effective resource management and planning. So, the objective of this research is to delineate and assess climatic zones within East Azerbaijan province regarding their potential evapotranspiration rates. This involves examining spatial differences and temporal trends across key locations within the province. By gathering data over multiple years, this study aims to identify patterns that can inform water resource management strategies and agricultural practices in the region.
 
Methodology
The study utilize MODIS satellite data, renowned for its high spatial and temporal resolution, to evaluate PET across key meteorological stations within East Azerbaijan province. These stations include Hashtrood, Bonab, Jolfa, Kaleybar, Marand, Maragheh, Mianeh, Sahand, Sarab, and Tabriz, providing a comprehensive coverage of diverse climatic zones. Data collection involved extracting PET values over a 20-year period, from 2005 to 2024, with data originally provided in 8-day intervals. To transform these into daily data points suitable for fine-scale analysis, advanced data processing techniques, including a Kalman filter for noise reduction and a cubic spline interpolation method for data densification were employed. These methods were implemented through custom coding in the Python environment within Google Earth Engine, enhancing data usability for detailed climatic analysis. For spatial representation, ArcGIS software was used to perform geostatistical analysis, employing Kriging and Inverse Distance Weighting (IDW) interpolation techniques. These methodologies enable the transformation of point data into spatial maps, considering the intricate spatial heterogeneity of PET across the province. By creating annual PET maps for key years (2005, 2010, 2015, 2020, and 2024), the study identifies trends and spatial variations significant for regional planning and management.
 
Results
The spatial and temporal analysis of PET across East Azerbaijan Province reveals significant and varied patterns. Notably, Jolfa exhibited the highest mean annual PET values, consistently exceeding 800 mm/year, indicating distinct climatic conditions compared to other regions. In contrast, stations like Sarab and Kaleybar recorded lower annual PET values, averaging around 600 mm/year, which can be attributed to their higher altitudes and corresponding cooler climate. A comparative analysis of PET between 2005 and 2024 highlights a noticeable increase across all stations, with an average rise of 1.5% per year. This increment is particularly pronounced in lower altitude stations such as Bonab and Mianeh, where PET values have increased approximately 30% over the two decades. These variations suggest an escalating evaporative demand, potentially stressing local water resources. Furthermore, the PET rise aligns with increased temperatures and variable precipitation patterns observed in the region, underscoring shifts induced by climatic change. Specifically, Tabriz and Marand showed marked sensitivity to climatic changes, with notable variations in potential evapotranspiration (PET) closely tracking annual temperature changes greater than 0.3 °C. The impact of urbanization and agriculture is evident in stations like Maragheh and Marand, where increased PET values align with expansive agricultural practices and urban expansion. In terms of temporal trends, the period from 2015 to 2020 marked the most significant changes, with PET increases reaching their highest levels during drought years, corroborating the strong influence of water availability and climatic extremes on evapotranspiration rates. The integration of MODIS data and refined interpolation methods such as Kriging provided highly accurate PET maps, with a standard deviation of less than 5% from observed values in field trials. This precision empowers robust spatial analysis, crucial for resource allocation and environmental management.
 
Conclusion
The comprehensive study conducted on the PET across East Azerbaijan Province reveals an increasing trend from 2005 to 2024. This trend is of particular concern, as it indicates a significant shift in the region’s climatic behavior, with implications for both ecological stability and resource management. The rise in PET values can largely be attributed to factors such as climate change, characterized by increased temperatures and altered precipitation patterns, which intensify evaporation processes. Human activities also play a substantial role in this upward trend. Urban expansion, deforestation, and changes in land use have altered surface conditions, subsequently affecting local microclimates and evaporation rates. Additionally, the study highlights the important role of technological advancements, such as the use of MODIS sensor data, in monitoring and analyzing spatial and temporal changes in climatic parameters like PET. By employing sophisticated interpolation methods like Kriging and IDW through ArcGIS, the research offers precise zoning of climatic zones, facilitating targeted interventions.
Author Contributions
Conceptualization, Z.R. and S.S.; methodology, Z.R. and M.M..; software, Z.R. and M.M.; validation, M.M. and S.S.; formal analysis, Z.R. and M.M.; investigation, Z.R. and M.M.; resources, S.S.; data curation, Z.R. and M.M.; writing—original draft preparation, Z.R. and M.M.; writing–review and editing, S.S.; visualization, Z.R. and M.M.; supervision, S.S.; project administration, S.S.; All authors have read and agreed to the published version of the manuscript.
Data Availability Statement
Data is available on reasonable request from the authors.
Acknowledgements
The authors would like to sincerely thank the anonymous reviewers for their valuable comments and constructive suggestions, which greatly contributed to improving the quality of this manuscript. The authors also wish to express their gratitude to the editor for their guidance and support throughout the review process.
Conflict of interest
The authors declare no conflict of interest.
Ethical considerations
The authors avoided data fabrication, falsification, plagiarism, and misconduct.