Ech-Chahdi et al. (2026) Long-term monitoring of surface water dynamics using remote sensing data: A case study of Al Wahda dam, Morocco

Identification

• Journal: BIO Web of Conferences
• Year: 2026
• Date: 2026-01-01
• Authors: Khadija El Ouazani Ech-Chahdi, Abdelaziz El-Bouhali, Mhamed Amyay
• DOI: 10.1051/bioconf/202621101014

Research Groups

• Sidi Mohamed Ben Abdellah University. Department of Geography, FLSH Sais-Fez, Morocco
• Ibn Zohr University. ESEAD Laboratory, FLASH Ait Melloul, Morocco

Short Summary

This study monitored the spatiotemporal evolution of Al Wahda dam's water surface area in Morocco from 1997-2024 using remote sensing and analyzed the impact of rainfall variability (SPI-12), revealing a significant correlation between dam surface area fluctuations and climatic conditions.

Objective

• To monitor the spatiotemporal evolution of the Al Wahda dam's water surface area using the Normalized Difference Water Index (NDWI) derived from remote sensing data.
• To highlight the impact of rainfall variability and drought on the reservoir’s surface area by calculating the Standardized Precipitation Index (SPI).

Study Configuration

• Spatial Scale: Al Wahda dam, located in the Ouergha Basin, northwestern Morocco.
• Temporal Scale: 28-year period (1997–2024) for water surface area monitoring; 34-year period (1990–2023) for rainfall data analysis.

Methodology and Data

• Models used:
  • Normalized Difference Water Index (NDWI) for water surface area extraction.
  • Otsu algorithm for NDWI classification (water/non-water thresholding).
  • Standardized Precipitation Index (SPI-12) for hydrological drought analysis.
• Data sources:
  • Multispectral Landsat satellite images (TM, OLI, and OLI-2) from the U.S. Geological Survey (USGS Earth Explorer), acquired in April.
  • Rainfall data from four stations (Bab Ouander, Jbel Oudeka, Galaz, and Mjaara) provided by the Sebou Hydraulic Basin Agency.

Main Results

• The dam's water surface area exhibited significant fluctuations, increasing from approximately 86 km² in 1997 to 111 km² in 1998, and decreasing to 72 km² in 2016.
• A moderate positive and statistically significant correlation (r = 0.55, p < 0.05) was found between the SPI-12 index (Mjaara Station) and the dam's water surface area.
• For each unit increase in the SPI-12 index, the water surface area of the dam increased by approximately 8.6 km².
• Most drought periods (negative SPI-12 values) coincided with marked shrinkage in the dam's water surface area, while positive SPI-12 values led to pronounced increases.
• The recent period (2019-2024) shows a slight trend toward relative stabilization, but surface areas remain lower than those observed during several earlier periods.

Contributions

• Provides a comprehensive long-term (28-year) spatiotemporal monitoring of a strategic dam's water surface area in Morocco using remote sensing.
• Quantifies the direct influence of hydrological drought (SPI-12) on dam water surface dynamics, including a specific sensitivity value (8.6 km² per SPI-12 unit).
• Highlights the combined impact of climatic conditions (rainfall variability, increasing temperatures) and anthropogenic pressures (irrigation demand, sedimentation) on dam performance in a climate change hotspot.

Funding

Not applicable.

Citation

@article{EchChahdi2026Longterm,
  author = {Ech-Chahdi, Khadija El Ouazani and El-Bouhali, Abdelaziz and Amyay, Mhamed},
  title = {Long-term monitoring of surface water dynamics using remote sensing data: A case study of Al Wahda dam, Morocco},
  journal = {BIO Web of Conferences},
  year = {2026},
  doi = {10.1051/bioconf/202621101014},
  url = {https://doi.org/10.1051/bioconf/202621101014}
}