Landslides in Zomba District of Southern Malawi after cyclone Ana in January 2022: Mechanisms of generation

Abstract

Landslides are caused by natural and anthropogenic factors. Some of the factors include heavy rainfall, steep slope, soil types and land use/land cover changes. On 24^th of January 2022, the Zomba district was affected by the Tropical storm Ana, which brought strong winds and heavy precipitation and caused landslides. The landslides resulted in loss of soil fertility around areas close to the mountain. This study focuses on the amount of rainfall that caused the landslides and explores other factors that could have contributed to the landslides in the Zomba Mountain. Therefore, this study might be useful to the local council when planning for disaster preparedness in the area. The data used in this study were daily rainfall from October 1983 to March 2022 and Landsat images for 2018 and 2021. The 2022 satellite images were not available for analysis. Digital elevation model, contour map and soil texture map were also used. The results of the study showed that 145 mm was the amount of rainfall received in 24 hours that triggered the landslides. The area received the same amount of precipitation in January 2015; however, there are no records of landslides in connection with that rainfall event. It is therefore likely that heavy rainfall was not the only factor that led to the landslides in the Zomba Mountain in January 2022. It is likely that a combination of other factors also contributed, such as the presence of clay and sand particles, high slope gradient and not the least deforestation. All these factors are strong candidates to contribute to slope instability resulting in slope failure.