Journal of Ecohydrology

Journal of Ecohydrology

Machine Learning–Based Downscaling of GLDAS Surface Soil Moisture and Performance Evaluation Across Climatic Regions of Iran

Document Type : Research Article

Authors
Seyedeh Mahsa Mousavi Reineh 1
Saman Javadi 1
Hossein Yousefi Sahzabi 2
Amin Reza Neshat 3
Ali Reza Massah Bavani 4
1 Department of Water Engineering, Department of Water Engineering, Aburaihan Campus, University of Tehran, Iran
2 Faculty of Interdisciplinary Science and Technology, University of Tehran, Iran
3 Department of Civil Engineering, SR.C., Islamic Azad University, Tehran, Iran
4 Department of Water Engineering, Aburaihan Campus,, University of Tehran
10.22059/ije.2026.404312.1891
Abstract
Research Topic: Due to scarce in-situ soil moisture observations and coarse reanalysis resolution, downscaling GLDAS surface soil moisture (SSM) using machine learning is essential.
 
Objective: This study evaluates the performance of machine learning algorithms for downscaling GLDAS SSM across Iran’s diverse climatic zones.
 
Method: In this study, Random Forest (RF), XGBoost, CatBoost, and LightGBM algorithms were employed for downscaling process. Model inputs comprised station-based climatic variables (minimum and maximum temperature, precipitation, and evaporation) and spatial attributes on a monthly scale over a 31-year period. The models were trained using GLDAS surface soil moisture values, producing downscaled soil moisture at a higher spatial resolution as output. In-situ soil moisture observations were utilized exclusively for independent validation. The dataset was partitioned into training (80%) and testing (20%) sets based on a chronological order.
 
Results: CatBoost demonstrated a strong ability to capture nonlinear soil moisture patterns, achieving coefficients of determination exceeding 0.73 across all climatic zones considered in this study. Although model accuracy varied depending on climatic characteristics and the spatial distribution of reference data, CatBoost was identified as an efficient algorithm for soil moisture prediction over the study area due to its high generalization capability and satisfactory performance in independent national-scale validation (R² = 0.607, RMSE = 4.286, Bias = 2.131).
 
Conclusions: The findings indicate that machine learning frameworks, particularly CatBoost, offer a reliable approach for downscaling GLDAS SSM. Given its high generalization capability across varying hydro-climatic conditions, CatBoost is recommended for enhancing drought monitoring and water resource management in data-scarce regions.
Keywords
Downscaling
Soil Moisture
GLDAS Data
Machine Learning
CatBoost
Subjects
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Journal of Ecohydrology
Volume 12, Issue 4
Autumn 2026
Pages 982-1004

  • Receive Date 14 October 2025
  • Revise Date 04 November 2025
  • Accept Date 16 December 2025
  • First Publish Date 22 December 2025
  • Publish Date 22 December 2025