Karimi et al. (2025) Robust assessment of snow persistence dynamics in Iran (2002–2024) using MODIS satellite imagery and multi-source evaluation

Identification

• Journal: Remote Sensing Applications Society and Environment
• Year: 2025
• Date: 2025-11-01
• Authors: Neamat Karimi, Amirhossein Sarbazvatan
• DOI: 10.1016/j.rsase.2025.101806

Research Groups

Department of Water Resources Research, Water Research Institute, Tehran, Iran

Short Summary

This study provides a comprehensive assessment of snow persistence (SP) variability across Iran from 2002 to 2024 using MODIS satellite imagery. It reveals a significant nationwide decline in SP, averaging −6.2% (approximately 23 snow-covered days), primarily driven by warming trends, with the most pronounced losses at mid-elevations.

Objective

• To provide a comprehensive assessment of snow persistence (SP) variability across Iran from 2002 to 2024 and identify its climatic drivers.

Study Configuration

• Spatial Scale: Iran, with analysis limited to regions with mean annual SP > 2 %. MODIS data resolution is 500 m.
• Temporal Scale: 2002–2024 (22 years), using 8-day composite products.

Methodology and Data

• Models used: Mann–Kendall test, Theil–Sen slope estimator, Random Forest model.
• Data sources: MODIS MOD09A1 8-day surface reflectance product (500 m), Normalized Difference Snow Index (NDSI ≥ 0.4) for snow identification, Landsat-8/9, Sentinel-2, ERA5 reanalysis, FLDAS reanalysis.

Main Results

• A significant nationwide decline in SP was observed, averaging −6.2 %, equivalent to an average reduction of approximately 23 snow-covered days over 22 years.
• The most pronounced SP decreases occurred in the Zagros and Alborz Mountains.
• SP exhibited a U-shaped pattern along the elevation gradient, with the strongest losses (approximately −7 %) between 1900 m and 2600 m above sea level (a.s.l.). High elevations (>2600 m a.s.l.) showed relatively stable SP.
• A significant upward shift in the mean elevation of snow-covered areas was observed (29 m per year; cumulative +638 m), reflecting elevation-dependent warming (0.07–0.09 °C per year).
• Temperature accounted for 58 % of the total influence on SP decline, compared to 42 % for precipitation, confirming warming trends as the dominant climatic driver.
• Phenological analysis revealed minimal change in the first snowy day (FSD), but the last snowy day (LSD) advanced by approximately 23 days, shortening the snow season duration.
• MODIS-derived SP results showed strong agreement with high-resolution composites from Landsat-8/9 and Sentinel-2 imagery (R² = 0.88) and consistent spatial patterns with ERA5 and FLDAS reanalysis datasets.

Contributions

• Provides the first robust, comprehensive assessment of snow persistence dynamics across Iran over a 22-year period (2002–2024) using MODIS satellite imagery.
• Quantifies elevation-dependent changes in snow persistence and the significant upward shift of snow-covered areas, linking it to elevation-dependent warming.
• Identifies temperature as the dominant climatic driver for snow persistence decline in Iran, providing a quantitative distinction from precipitation's influence.
• Utilizes a multi-source evaluation approach, validating MODIS-derived SP with high-resolution satellite imagery (Landsat-8/9, Sentinel-2) and reanalysis datasets (ERA5, FLDAS).
• Highlights the urgent need for adaptive water-resource management and climate-resilience strategies in Iran's snow-dependent regions.

Funding

Not explicitly stated in the provided text.

Citation

@article{Karimi2025Robust,
  author = {Karimi, Neamat and Sarbazvatan, Amirhossein},
  title = {Robust assessment of snow persistence dynamics in Iran (2002–2024) using MODIS satellite imagery and multi-source evaluation},
  journal = {Remote Sensing Applications Society and Environment},
  year = {2025},
  doi = {10.1016/j.rsase.2025.101806},
  url = {https://doi.org/10.1016/j.rsase.2025.101806}
}