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ENVIRONMENTAL CHANGE IN KENYA

The Tana River Basin in Kenya covers approximately 17,000 km² and is home to 5.3 million people (DW 2018). The basin encompasses Mount Kenya and the Aberdare highlands with elevations ranging from 4,500m at Mount Kenya to about 400m above sea level in the east of the catchment (Marshall 2011). The rainfall patterns in the basin have changed drastically over recent decades and have become more sporadic with more torrential rains of high intensity.

This particularly true for the Upper Tana River Basin in Kenya and is exemplified by the disastrous May 2018 flash floods when the highest rainfall in 50 years hit the area. These floods caused extensive damage to the village communities with 100 dead and almost 300,000 people displaced from their homes (DW 2018). Much of the damage was also visible through scarring on the local landscape as a result of large mudslides. The Tana River basin is characterized by relatively fertile soils as it is derived from volcanic parent material. These physical conditions alongside the high rainfall result in prime conditions for agricultural use. As such, since before the 1960s the Tana River Basin has been intensively farmed. This has resulted in degraded soils which are highly vulnerable to erosion (DW 2018). In order to address the increasing threat of flash floods, communities in the basin engineered practical solutions that would minimize the effects of a similar flash flood event. The primary variable affecting flash floods that the locals could alter and improve was the stability of the riverbanks and land slopes and the soil moisture content. Due to deforestation and soil degradation, soil moisture content is highly variable in the basin. Soil moisture content plays a huge role in modulating soil stability and therefore the scale of flash flood events (Tuttle & Salvucci 2014).

Figure 1: Bamboo planting projects can be seen in the Upper Tana River Basin to offer soil stability (source)

To address the environmental issues in the Upper Tana Basin, large scale bamboo planting projects have been introduced to the area in close proximity to the Tana River and its tributaries in order to offer protection in the form of controlling soil moisture content. The bamboo planting scheme was strategically placed in riparian and landslide-prone areas of the Tana river catchment area as this would reduce sediments flowing into the river and stabilise land that is prone to landslides. In theory this would prevent catastrophic floods on a similar scale to the May 2018 flash floods (DW 2018). This scheme has drastically altered the natural environment. The slopes of the river have become greener, particularly when compared to the nearby province of Nyanza which has experienced high levels of deforestation and where this type of scheme has not yet been put in place. Unlike other tree species that take up to 15 to 30 years to form a canopy, bamboo can form a canopy within the first four years of being planted (DW 2018). Bamboo canopy protects the soil and reduces evaporation, thus rehabilitating highly degraded areas faster. The bamboo-rooting system also helps to retain water in the ground and to bind the soil together thereby reducing the quantity of sediments that enter the rivers downstream (DW 2018).

Small holder farmers in the Upper Tana River basin have planted approximately 65,000 bamboo seedlings since 2018 (DW 2018). Although severe flood events still occur due to the nature of the climate in Kenya, the magnitude of many of the flood events has been reduced due to the bamboo planting scheme. In addition to this, the bamboo is also utilised as an agricultural resource, with opportunities for locals to improve their economic livelihoods through selling bamboo products such as firewood, charcoal and fencing and building materials (Huho and Kosonei 2014). Therefore, the scheme has been considered as largely successful.

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