Integrating GIS and AHP to Assess and Mitigate Landslide Hazards in Ethiopia’s East Gojjam Region

A study in Ethiopia's East Gojjam zone used GIS and AHP methods to create a landslide hazard map, identifying human activities and rainfall as key risk factors, offering crucial insights for disaster mitigation and future planning.

In a region where the landscape itself poses a significant threat to the lives and livelihoods of its residents, the East Gojjam zone of northwestern Ethiopia has long been vulnerable to landslides. These natural disasters are not just sporadic events; they have become a recurrent menace, particularly exacerbated during the rainy seasons. This area, crucial to Ethiopia's economy and a vital source of water for the Grand Ethiopian Renaissance Dam (GERD), has been the subject of a comprehensive study conducted by Chalachew Tesfa and Demeke Sewnet from Debre Markos University. Their research aimed to map out landslide hazard zones using a sophisticated Geographic Information System (GIS)-based approach combined with the Analytical Hierarchy Process (AHP), a well-established multi-criteria decision-making (MCDM) tool. The study's objective was clear: to create a detailed and accurate landslide hazard zonation (LHZ) map that could serve as a vital resource for future urban planning, environmental conservation, and disaster mitigation efforts.

The East Gojjam Zone: A High-Risk Region

The East Gojjam zone is characterized by its rugged topography, including highlands and mountainous regions, which are inherently prone to landslides. Over the years, these landslides have caused significant damage, disrupting transportation, destroying farmland, and endangering the lives of those who live and work in the area. Given the economic importance of this region, as well as its role in feeding the GERD, understanding and mitigating the risks posed by landslides has become a priority. The researchers employed a comprehensive methodology to address this challenge. They began with an extensive inventory of past landslides, documenting over 700 sites that had been affected by these events. This inventory was crucial in understanding the patterns and frequencies of landslides in the area and provided a foundation for predicting future hazards.

Analyzing Causative Factors of Landslides

To accurately predict landslide susceptibility, the researchers analyzed a range of causative factors. These included the slope degree, land use, proximity to roads and rivers, rainfall, and the underlying geology of the region. Each of these factors was carefully evaluated and assigned a weight based on its relative importance in contributing to landslide occurrences. For instance, areas with steep slopes, poor vegetation cover, and close proximity to rivers or roads were identified as particularly vulnerable. The GIS tools allowed for the integration of these diverse datasets, creating a detailed map that highlighted the most at-risk areas. One of the key findings of the study was the significant role of human activities in exacerbating landslide risks. The expansion of agricultural activities, deforestation, and the construction of roads were found to be major contributors to slope instability. In particular, road construction, which often involves cutting into steep slopes, was identified as a major trigger for landslides. The vibrations from heavy vehicles and the removal of vegetation further destabilize these areas, leading to a higher frequency of landslide events.

Rainfall’s Role in Triggering Landslides

Rainfall, another critical factor, was found to be a significant driver of landslides in the East Gojjam zone. The region experiences substantial rainfall, particularly during the monsoon season, which increases the likelihood of landslides. The researchers noted that the combination of heavy rainfall and the region's geological conditions characterized by weathered and disintegrated rock masses creates a perfect storm for landslide occurrences. The validation of the LHZ map against historical landslide data demonstrated its accuracy. More than 80% of past landslides fell within the areas designated as high hazard zones on the map, confirming the effectiveness of the methodology used. This validation is critical, as it ensures that the LHZ map can be reliably used for future planning and mitigation efforts.

A Tool for Safeguarding the Region’s Future

The implications of this study are far-reaching. The LHZ map produced by Tesfa and Sewnet is not just a static document; it is a dynamic tool that can guide future development in the region. Urban planners can use it to avoid high-risk areas when designing new infrastructure projects. Environmentalists can leverage the map to advocate for conservation efforts that protect the most vulnerable landscapes. Disaster management agencies can use it to prioritize areas for landslide prevention measures, such as reforestation or the construction of retaining walls. Moreover, the study highlights the need for ongoing monitoring and updating of the LHZ map. As environmental conditions change and human activities continue to alter the landscape, the risks associated with landslides will evolve. Continuous data collection and analysis are essential to maintaining the accuracy and relevance of the hazard zonation. In conclusion, the study by Tesfa and Sewnet represents a significant step forward in understanding and mitigating landslide risks in the East Gojjam zone. Their work provides a model for other regions facing similar challenges and underscores the importance of integrating advanced GIS techniques with local knowledge and expertise. As climate change continues to impact weather patterns and increase the frequency of extreme events, such as heavy rainfall, the importance of studies like this cannot be overstated. The LHZ map they have produced is more than just a research outcome it is a critical tool for safeguarding the future of a region that is vital to Ethiopia’s economic and environmental well-being.