DESIGNING A TERRITORIAL EARLY WARNING SYSTEM FOR RAINFALL-INDUCED LANDSLIDES: THE CASE OF BLANTYRE CITY, MALAWI.

Landslides triggered by heavy rainfall pose a significant threat to Blantyre City. Climate change is expected to further increase frequency and intensity of these events. The overall goal of this study was to design a Territorial Early Warning System that provides sufficient lead time. For this goal, the study involved comprehensive review of relevant literature (including published and unpublished sources) to identify relevant components that constitute the EWS. Additionally, a susceptibility analysis using the Frequency Ratio (FR) Model was conducted with historical landslide data (from 2022 to 20223) and Causative Factors (including 2023 annual rainfall as trigger) to create landslide susceptibility map for Blantyre City. The susceptibility map revealed areas surrounding hills and mountains such as Soche, Chigumula, Bangwe, Bangwe Mthandizi, Mpingwe, Nyambadwe, Michiru and Ndirande to be highly susceptible to rainfall-induced landslides. The proposed EWS consists of a network of sensors; rain gauges for monitoring rainfall, extensometers for measuring slope movement, and piezometers for monitoring pore pressure. These sensors will collect and transmit data (rainfall amounts, pore pressure, and slope movement) to an administrative analysis and forecasting center. The center will analyze the data and trigger phased warnings (gradually escalating warnings based on the severity of the threat) to all key stakeholders through various communication channels, especially media outlets. It has been emphasized that the proposed system should be managed by relevant government institutions in collaboration with other key departments and stakeholders due to the multidisciplinary nature of Rainfall-Induced landslides forecasts.

Additionally, a susceptibility analysis using the Frequency Ratio (FR) Model was conducted with historical landslide data (from 2022 to 20223) and Causative Factors (including 2023 annual rainfall as trigger) to create landslide susceptibility map for Blantyre City. The susceptibility map revealed areas surrounding hills and mountains such as Soche, Chigumula, Bangwe, Bangwe Mthandizi, Mpingwe, Nyambadwe, Michiru and Ndirande to be highly susceptible to rainfall-induced landslides. The center will analyze the data and trigger phased warnings (gradually escalating warnings based on the severity of the threat) to all key stakeholders through various communication channels, especially media outlets. It has been emphasized that the proposed system should be managed by relevant government institutions in collaboration with other key departments and stakeholders due to the multidisciplinary nature of Rainfall-Induced landslides forecasts.

The study was conducted in Blantyre City (in Blantyre district), southern region of Malawi. This city was established by the Scottish missionaries in the 1870s and declared a planning area in 1 897 (Mawenda et al., 2020). Its rugged terrain characterized by multiple hills and river systems makes it vulnerable to landslides. It has varied topography ranging from an elevation of about 780 to 1,599 meters above sea level and it lies within the latitude 15◦47010” S and longitude 35◦00020.10” E, as shown in Figure 1. The main mountains include, Ndirande, Soche, Bangwe and Michiru (Mawenda et al., 2020). And the main livers include Mudi, Likhubula, Limbe, Chisombezi and Lucheza.
Blantyre city currently hosts nearly 5% of Malawi’s national population and it boasts the highest population density in the country. It has 23 wards covering an area of 240.2 km2 with 800,264 people and 3,332 people/km2 as its total population and population density respectively (National Statistics Office, 2021). The literacy rate for Blantyre city is 90%. Generally, the rainy season is from November to April, with continuing light cold showers locally known as chiperoni from the end of May to July. The average annual rainfall is about 1,127 mm, of which about 80% falls within 3.5 months between November and March (DCCMSs, 2022). Rapid and unplanned urban growth has led to adverse environmental and social consequences.

Traditional authority: Blantyre City

District: Blantyre

Coordinates: -15.7955, 35.04405