Using Remote Sensing in Evaluating Geological Hazards Triggered by Climate Change Events in Malawi
Authors: Gulule Ellasy , Chiwona Annock Gabriel , Nthara Tamara 
Published: March 2024

Climate change can enhance extreme weather conditions thereby significantly influencing change in precipitation patterns. This results in change to both rainfall intensity and distribution in many parts of the world. The increase in rainfall intensity triger hazards such as flooding and geohazards such as landslides. The impact and scale of flooding hazards are well evaluated and documented. However, geohazards from extreme weather events are not well documented in many developing countries making it difficult to quantify trends, frequency and spatial distribution. This knowledge gap is particularly evident in countries like Malawi, which have been significantly impacted by climate-related extremes, including cyclones. For instance, Tropical Cyclone Freddy which made a landfall in Southern Africa, induced above normal torrential rains in Malawi in March 2023. These rains triggered landslides, mudslides, debris flow and floods which affected 14 districts in the southern region of Malawi (GoM,2023).The size, magnitude and effect of flood hazard from the Tropical Cyclone Freddy was well studied. However, quantifying and mapping spatial patterns of geohazards was not well documented and less prioritized.
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In this study, we used sentinel 2 and rainfall data to a) characterise geohazard from extreme weather events, b) develope inventory for geohazards c) quantify the relationship between extreme weather events and occurrence of geohazard in southern parts of Malawi. Field survey was conducted for ground truthing in the landslide scarps in Blantyre, Thyolo and Zomba districts to improve accuracy of mapping and validating data from remote sensing analysis. Preliminery results on inventory indicate more than 10 landslides within the study area with Mulanje, Thyolo and&#160; Zomba registering highest number of landslides. These ranged in size from localized to more than 30m along the slope. On the time of occurrence, it was observed that most of the hazards occurred on different times even if they were exposed to same extreme weather, but all occured within a period of four days from onset of high intensity rains. This correlates to the period of high rainfall intensity in many areas. The characteristics of the material from the landslide scarps varied from loam clay, boulders to debri . However, most of the areas were charecterised with steep slopes of above 60o slope angle. Thus, other than extreme weather, landslides were highly influenced by the slope angle. Type of material on the slope had minor influence and this was in agreement with the results from regression analysis. These study results will act as guide to predict the occurrence of future geohazards and understand their patterns which is key in predicting future occurrences of the hazards.
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Keywords: Remote Sensing, climate change, Cyclone Freddy, geohazards, Malawi
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References
Government of Malawi. 2023. Malawi 2023 Tropical Cyclone Freddy Post-Disaster Needs Assessment. Lilongwe: Government of Malawi.