Irifi et al. (2026) Landscape Dynamics of Marly Slopes in the Lower Valley of Wadi Tamri (Morocco): An Integrated Approach Using Geomorphometry, Toposequences, and Remote Sensing

Identification

• Journal: Cuadernos de Investigación Geográfica
• Year: 2026
• Date: 2026-03-23
• Authors: Hicham Irifi, Abdellatif Tribak
• DOI: 10.18172/cig.7072

Research Groups

• MNADSS – School of Geography, Sidi Mohamed Ben Abdellah University, Fez-Saïs, Morocco.

Short Summary

This study investigates the landscape dynamics of marly slopes in the lower Wadi Tamri valley, Morocco, using an integrated approach of geomorphometry, remote sensing, and field observations. It reveals significant landscape degradation, characterized by a substantial loss of Argan forest cover and an increase in exposed marly substrate, driven by recurrent droughts and human activities, leading to accelerated gully erosion and slope instability.

Objective

• To understand the complex interplay of biotic, abiotic, and human factors shaping the landscape dynamics of marly slopes in the lower Wadi Tamri valley.
• To model relationships between geomorphometric indices, land use changes, and gullying processes using multi-temporal Digital Elevation Models (DEMs) and remote sensing.
• To assess the evolution of gullying and land use changes over time, linking them to climatic conditions and anthropogenic pressures.
• To provide a scientific foundation for regional soil and water conservation strategies and propose integrated landscape management axes for edaphic and forest resources.

Study Configuration

• Spatial Scale: Lower valley of Wadi Tamri basin, Atlantic High Atlas, Morocco, focusing on two landscape units: Aziar (232.91 km²) and Ighzer Ougadir (10.16 km²).
• Temporal Scale:
  • Gully evolution and hydrographic analysis: 2007 and 2014.
  • Land use/land cover changes: 1984, 2000, and 2022.
  • Field observations and toposequences: 2020-2022.
  • Climate data analysis: 1981-2022.

Methodology and Data

• Models used:
  • Geomorphometric indices: Gravelius Index, Equivalent Rectangle, Basin Relief, Useful Height Difference, Theoretical Slope, Useful Slope, Specific Height Difference, Dissection Index, Elongation Ratio, Hypsometric Integral, Hydrographic Density, Drainage Density, Length Ratio, Confluence Ratio.
  • Hydrological indices: Topographic Wetness Index (TWI), Sediment Transport Index (STI), Stream Power Index (SPI).
  • Climate index: Standardized Precipitation Index (SPI).
  • Stream ordering: Strahler's classification system.
  • Land use classification: Maximum Likelihood Classification algorithm.
• Data sources:
  • Digital Elevation Models (DEMs): ALOS-PALSAR (2007) and SRTM (2014), both with 30 meter resolution, from USGS and ASF.
  • Satellite imagery: Landsat 5 TM (1984), Landsat 7 ETM+ (2000), Landsat 8 OLI-TIRS (2022), all with 30 meter resolution, from USGS.
  • Climate data: Monthly and annual precipitation from Climate NASA Power website (1981-2022).
  • Field observations: 38 sampling sites, transects, and sample plots conducted between 2020 and 2022, including erosion forms, ecological factors, and human activities.
  • Geological map of Taghazout 1/100000 (1971).
  • Google Earth Pro for visual analysis and validation.

Main Results

• Gully Dynamics: Hydrographic density in the Ighzer Ougadir unit increased from 543 km⁻² in 2007 to 598.59 km⁻² in 2014, indicating a 5% increase in gullying. The Aziar unit saw an increase in first-order gullies from 69,253 to 77,999 between 2007 and 2014, with an overall increase in drainage density in both units.
• Geomorphometric Analysis: Both units exhibit highly dissected landscapes (Dissection Index: 0.87 for Ighzer Ougadir, 0.82 for Aziar) and elongated basins with high relief (Elongation Ratio: 0.60 and 0.41, respectively). Hypsometric integrals (0.49 and 0.5) suggest a landscape transitioning from youth to mature geomorphic evolution.
• Erosion Potential: TWI analysis shows widespread dry soil conditions (~40% 'very dry' cells), with wetter areas confined to main watercourses. STI analysis indicates the highest erosive potential (STI ≥170) along the hydrographic network (orders 4-7) and ravines. SPI analysis revealed a significant increase in gully erosive activity from 2007 to 2014, linked to forest cover decrease and rainfall variability.
• Land Use Change (1984-2022): A significant regression of Argan forest cover (-26% in Aziar) occurred, replaced by expanding marly rock (+5%) and cultivated soils (+84% in Aziar). The marl substratum in Aziar increased by 891.30 hectares between 2000 and 2022. Gullying affects 7% (1,668 hectares) of the total area, with 65% (15,115 hectares) of marl slopes highly susceptible.
• Climate Variability (1981-2022): Rainfall has significantly decreased since the early 2000s (below 260 mm average), with six prolonged dry spells, particularly severe from 1999-2009. The 12-month SPI confirms severe drought conditions, with increased frequency and intensity of prolonged droughts since 2000.
• Toposequences: Marly slopes are severely impacted by erosion and gullying, forming badlands, primarily on Hauterivian formations. Erosion is driven by lithological contrasts, tectonics, climate, low vegetation cover, and human activities, leading to bare, stripped, and ruiniform landscapes. Piping erosion is also significant.

Contributions

• Provides a comprehensive, integrated analysis of landscape dynamics and gully evolution in vulnerable marly slopes, addressing a significant gap in previous research by combining geomorphometry, multi-temporal remote sensing, and field-based toposequences.
• Quantifies the impacts of land use changes and rainfall variability on hydrographic networks and gully development over multi-decadal periods.
• Offers valuable insights into the complex interactions between biotic, abiotic, and human factors driving slope processes and land degradation.
• Establishes a scientific basis for developing regional soil and water conservation strategies and proposing integrated landscape management plans for the lower Wadi Tamri valley, serving as a model for broader application in similar Mediterranean environments.

Funding

No specific funding projects, programs, or reference codes were listed in the paper.

Citation

@article{Irifi2026Landscape,
  author = {Irifi, Hicham and Tribak, Abdellatif},
  title = {Landscape Dynamics of Marly Slopes in the Lower Valley of Wadi Tamri (Morocco): An Integrated Approach Using Geomorphometry, Toposequences, and Remote Sensing},
  journal = {Cuadernos de Investigación Geográfica},
  year = {2026},
  doi = {10.18172/cig.7072},
  url = {https://doi.org/10.18172/cig.7072}
}