The effects of climate variability on Prosopis juliflora spread, vegetation trends and livestock dynamics in the drylands of Kenya

The effects of climate variability and Prosopis juliflora invasion on pastoral livestock production and pastoral livelihoods have not been assessed. A study was conducted to determine the effect of climate variability and Prosopis juliflora spread on other vegetation trends and livestock population dynamics in Kajiado County, Kenya. The effects of climate variability on the spread of Prosopis, vegetation dynamics and livestock populations were analysed. Monthly mean temperatures and total monthly rainfall amounts over the last 20 years varied widely, with mean temperatures ranging between 280C to 400C and total monthly rainfall amounts ranging from 0mm to 213mm, respectively. Cattle population decreased from 7,200 to 2,100 between 1990 and 2013and sheep and goats’ population increased from 14,000 to 20,000 in the same period. Climate, vegetation, and livestock population trends are analysed over the study period. Dry season vegetation and Prosopis NDVI trends, derived from MODIS 250m satellite imagery (2000-2014) were developed. Prosopis clusters, participatory mapped with the help of the local informants were used to isolate the Prosopis NDVI from the other vegetation. There was association between climate variability, Prosopis invasion and livestock population dynamics. Correlation coefficients for Prosopis spread against shoats are 0.2 and 0.3 and coefficients for Prosopis spread against rainfall were 0.4 and 0.2 in Olkiramatian and Ngurumani respectively. The rate of spread of P. juliflora was highest when rainfall was most erratic. Changes in land cover types and soil types were directly associated with the spread of Prosopis while specific areas likely to attract next spread of Prosopis were identified. Overall rainfall was highly variable in amounts, with declining trends; and the mean temperatures increased over the years of the study period while vegetation cover declined, especially during the long dry seasons. At the same time, Prosopis cover, sheep and goats populations increased while cattle populations declined.