**2. Study Area**

Kenya is an east African country (Figure 1). Kenya has a territorial area of 582,646 km<sup>2</sup> and a population of 41.8 million. The elevation of Kenya stretches from sea level in the coastal regions to over 5000 m above sea level (a.s.l.) at Mount Kenya. Geomorphologically, the landforms in Kenya are dominated by highlands in the central and the west regions, plains in the northeast and the coastal regions [20]. The Great Rift Valley (GRV) cuts through the western territory of Kenya from south to north, separating the highlands into two parts, the western highland and the eastern highland. The narrowest part of the rift valley basin is about 30 km near the Naivasha Lake, while the broadest of that is about 300 km in width near the Turkana Lake (Figure 1). The elevation difference in the GRV zone ranges from 500 to 1000 m.

**Figure 1.** General conditions of Kenya and the spatial distribution of historical landslides in Kenya.

Geologically, Kenya is mainly constituted of five parts [20]: (1) the Archean rocks, of which the major rock types are: shales, mudstones, greywackes, phyllites, and conglomerates; (2) the Proterozoic rocks, of which the major rock types are: rhyolites, basalts, quartzites, and conglomerates; (3) the Paleozoic and Mesozoic sediments, which were dominant by rock types of granites, granodiorites, and leucogranites; (4) the Tertiary/Quaternary volcanic rocks and sediments, of which the major rock types are: sands, marls, clays, conglomerates, and limestones; (5) the Pleistocene to Recent deposits, in which clays, diatomite, shales, and silts are major rock types.

Kenya has a mild climate with annual temperatures ranging from 16 to 26 degrees Celsius. The mean annual precipitation (MAP) in Kenya ranges from <200 mm to 2500 mm. The precipitation of Kenya is characterized by its nonuniform distribution in both time and space. From the historical meteorological data of the Jomo Kenyatta weather station (Figure 2), two distinct rainy seasons can be observed. One is from March to May (the heavy rainy season), and the other is from October to December (the light rainy season). The rest is the dry season. The spatial distribution of MAP is illustrated in Figure 3a. Because of the sudden elevation changes in the GRV zone (from highland to valley then to highland again), there is a sharp transition between wet and dry regions across the GRV zone in southwestern Kenya. Both sides of the GRV in this region had the highest value of MAP, while the northeastern and northern parts of Kenya had the lowest MAP of less than 800 mm. Kenya has experienced a series of geohazards arising from floods, storms, landslides, and debris/mudflows. Most of these geohazards are related to climate extremes [18,20]. Rainfall and human activities (farming, devegetation, construction, etc.) have triggered the majority of the landslides that have occurred in Kenya.

**Figure 2.** Statistics of monthly average precipitation and distribution of landslides in Kenya. Precipitation data was obtained from the Jomo Kenyatta weather station. Since no detailed information of the exact occurring moth of landslides in LS3, only LS1 and LS2 data were included in this figure.

**Figure 3.** List of landslide contribution factors: (**a**) MAP; (**b**) altitude; (**c**) slope; (**d**) aspect; (**e**) curvature; (**f**) TWI; (**g**) SPI; (**h**) soil texture; (**i**) land use; (**j**) landform.
