Water Erosion Risk Assessment in the Kenya Great Rift Valley Region: Fid-Bau Portal

Water Erosion Risk Assessment in the Kenya Great Rift Valley Region

George Watene / Lijun Yu / Yueping Nie / Jianfeng Zhu / Thomas Ngigi / Jean de Dieu Nambajimana / Benson Kenduiywo

The Kenya Great Rift Valley (KGRV) region unique landscape comprises of mountainous terrain, large valley-floor lakes, and agricultural lands bordered by extensive Arid and Semi-Arid Lands (ASALs). The East Africa (EA) region has received high amounts of rainfall in the recent past as evidenced by the rising lake levels in the GRV lakes. In Kenya, few studies have quantified soil loss at national scales and erosion rates information on these GRV lakes’ regional basins within the ASALs is lacking. This study used the Revised Universal Soil Loss Equation (RUSLE) model to estimate soil erosion rates between 1990 and 2015 in the Great Rift Valley region of Kenya which is approximately 84.5% ASAL. The mean erosion rates for both periods was estimated to be tolerable (6.26 t ha⁻¹ yr⁻¹ and 7.14 t ha⁻¹ yr⁻¹ in 1990 and 2015 respectively) resulting in total soil loss of 116 Mt yr⁻¹ and 132 Mt yr⁻¹ in 1990 and 2015 respectively. Approximately 83% and 81% of the erosive lands in KGRV fell under the low risk category (<10 t ha⁻¹ yr⁻¹) in 1990 and 2015 respectively while about 10% were classified under the top three conservation priority levels in 2015. Lake Nakuru basin had the highest erosion rate net change (4.19 t ha⁻¹ yr⁻¹) among the GRV lake basins with Lake Bogoria-Baringo recording annual soil loss rates >10 t ha⁻¹ yr⁻¹ in both years. The mountainous central parts of the KGRV with Andosol/Nitisols soils and high rainfall experienced a large change of land uses to croplands thus had highest soil loss net change (4.34 t ha⁻¹ yr⁻¹). In both years, forests recorded the lowest annual soil loss rates (<3.0 t ha⁻¹ yr⁻¹) while most of the ASAL districts presented erosion rates (<8 t ha⁻¹ yr⁻¹). Only 34% of all the protected areas were found to have erosion rates <10 t ha⁻¹ yr⁻¹ highlighting the need for effective anti-erosive measures.