Shafizadeh‐Moghadam et al. (2025) Pronounced decline in Iran's terrestrial water storage from GRACE and GRACE-FO associated with climate and unsustainable land-use change

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2025
• Date: 2025-12-01
• Authors: Hossein Shafizadeh‐Moghadam, Arezo Mohtaram, Atefe Arfa, Majid Delavar, Hojjat Mianabadi
• DOI: 10.1016/j.ejrh.2025.102954

Research Groups

• Department of Water Engineering and Management, Tarbiat Modares University, Tehran, Iran

Short Summary

This study quantifies the spatiotemporal decline in Iran's terrestrial water storage (TWSa) from 2002-2022 using GRACE/GRACE-FO data, attributing it to a complex interplay of climatic variability and unsustainable land-use changes, particularly intensified irrigation.

Objective

• To quantify the spatiotemporal dynamics of terrestrial water storage anomalies (TWSa) across Iran's six major river basins from 2002 to 2022 and statistically attribute these observed changes to hydroclimatic and anthropogenic drivers.

Study Configuration

• Spatial Scale: Iran, specifically its six major river basins: Caspian Sea, Persian Gulf and Gulf of Oman, Qareh Qum, Lake Urmia, Central Plateau, and Eastern Border.
• Temporal Scale: 2002–2022

Methodology and Data

• Models used: Mann-Kendall test, Sen's slope estimator, Generalized Additive Model (GAM) (using mgcv package in R), LightGBM algorithm (for GRACE data reconstruction).
• Data sources:
  • Terrestrial Water Storage Anomalies (TWSa): GRACE and GRACE-FO (RL06) data (arithmetic mean of CSR, JPL, and GFZ solutions), reconstructed TWSa from Mohtaram et al. (2024).
  • Land Use and Land Cover (LULC): GlobeLand30 dataset (2000, 2020).
  • Precipitation: Climate Hazards Group Infrared Precipitation with Station (CHIRPS) dataset (~5 km spatial resolution, daily temporal resolution).
  • Actual Evapotranspiration (ETa): MODIS products (500 m spatial resolution, 8-day temporal resolution).
  • Normalized Difference Vegetation Index (NDVI): MODIS-derived products (500 m spatial resolution, 16-day temporal resolution).

Main Results

• A nationwide decline in TWSa was observed at a rate of −2.06 mm yr⁻¹ (p = 0.07) across Iran.
• Statistically significant TWSa declines were found in the Caspian Sea basin (−3.77 mm yr⁻¹) and Lake Urmia basin (−3.46 mm yr⁻¹). Declines in other basins were consistent but not statistically significant.
• Individual hydroclimatic variables (precipitation, ETa) showed no statistically significant monotonic trends (p ≥ 0.05) across basins or nationally, but the Generalized Additive Model (GAM) identified them as considerable explanatory factors for TWSa variation.
• NDVI showed significant monotonic increases in the Caspian Sea (≈0.0009 units yr⁻¹), Persian Gulf–Gulf of Oman (≈0.0008 units yr⁻¹), Lake Urmia (≈0.0012 units yr⁻¹), Central Plateau (≈0.0002 units yr⁻¹), and Iran overall (≈0.0006 units yr⁻¹).
• Extensive land use and land cover (LULC) changes from 2000 to 2020 included cropland expansion (e.g., ~4000 km² in Central Plateau), widespread forest decline, and significant losses of grasslands (~150,000 km²) and shrublands (~180,000 km²) in the Central Plateau, leading to an increase of over 325,000 km² in bare land. Urban areas in the Caspian Sea region more than doubled.
• The divergence between increasing NDVI and declining TWSa is interpreted as evidence of unsustainable land and water management practices, primarily the expansion and/or intensification of irrigated agriculture.
• GAM results indicated that ETa and precipitation largely explain TWSa variability at the national scale and in interior basins (e.g., Iran: 64.7% deviance explained, 56.3% adjusted R²). NDVI contributed significantly only in the Persian Gulf–Gulf of Oman. TWSa variability in the Eastern Border was weakly explained (12.5% deviance explained), suggesting a larger role for unmodeled processes like groundwater abstraction.

Contributions

• Provides a comprehensive integration of satellite gravimetry (GRACE/GRACE-FO) with independent Earth observation and ancillary datasets to diagnose basin-scale water cycle trajectories in Iran, offering an operational and policy-relevant perspective in data-sparse regions.
• Quantifies the spatiotemporal dynamics of TWSa and attributes observed changes to the interplay of hydroclimatic variability and anthropogenic factors, particularly highlighting the role of unsustainable land management and intensified irrigation.
• Identifies specific basins most vulnerable to freshwater deficits and elucidates the cascading effects of climate shifts and land management practices on regional water balance.
• Offers evidence-based support for water management and adaptation planning in arid and semi-arid systems facing escalating water scarcity pressures.

Funding

Not explicitly mentioned in the provided text.

Citation

@article{ShafizadehMoghadam2025Pronounced,
  author = {Shafizadeh‐Moghadam, Hossein and Mohtaram, Arezo and Arfa, Atefe and Delavar, Majid and Mianabadi, Hojjat},
  title = {Pronounced decline in Iran's terrestrial water storage from GRACE and GRACE-FO associated with climate and unsustainable land-use change},
  journal = {Journal of Hydrology Regional Studies},
  year = {2025},
  doi = {10.1016/j.ejrh.2025.102954},
  url = {https://doi.org/10.1016/j.ejrh.2025.102954}
}