Assessing the impacts of climate variability and climate change on biodiversity in Lake Nakuru, Kenya

Abstract

Abstract. Wambui MB, Opere A, Githaiga MJ, Karanja FK. 2018. Assessing the impacts of climate variability and climate change on biodiversity in Lake Nakuru, Kenya. Bonorowo Wetlands 8: 13-24. This study evaluates the effects of the raised water levels and the flooding of Lake Nakuru and its surrounding areas on biodiversity, specifically, the phytoplankton and lesser flamingo communities, due to climate change and climate variability. The study reviewed and analyzed noticed climatic records from 2000 to 2014. Several methods were used to ascertain the past and current climatic parameters (temperature, rainfall, and evaporation) and the physicochemical characteristics of Lake Nakuru (conductivity, phytoplankton, lesser flamingos, and the lake depth). These included time series analysis and trend analysis, so Pearson’s correlation analysis was used to show a relationship between the alterations in lake conductivity to alterations in population estimates of the lesser flamingos and the phytoplankton. Data set extracted from the Coupled Model Inter-comparison Project Phase 5 (CMIP5) (IPCC Fifth Assessment Report (AR5) Atlas subset) models were subjected to time series analysis method where the future climate scenarios of near-surface temperature, rainfall, and evaporation were plotted for the period 2017 to 2100 (projection) for RCP2.6 and RCP8.5 relative to the baseline period 1971 to 2000 in Lake Nakuru were analyzed. The results were used to evaluate the impact of climate change on the lesser flamingos and phytoplankton abundance. It was noticed that there was a raise in the mean annual rainfall during the study period (2009 to 2014), which brought the increment in the lake’s surface area from a low area of 31.8 km² in January 2010 to a high of 54.7 km² in Sept 2013, indicating an increment of 22.9 km² (71.92% surface area increment). The mean conductivity of the lake also lessened, leading to the loss of phytoplankton on which flamingos feed, making them migrate. A strong positive correlation between conductivity and the lesser flamingo population was noticed, signifying that low conductivity affects the growth of phytoplankton. Since the lesser flamingos depend on the phytoplankton for their feed, this subsequently revealed that the phytoplankton density could be a notable predictor of the lesser flamingo occurrence in Lake Nakuru. A strong positive correlation was noticed between phytoplankton and the lesser flamingo population confirming that feed availability is a key determining factor of the lesser flamingo distribution in the lake. It is projected that there would be an increment in temperatures, rainfall, and evaporation for 2017 to 2100 under RCP2.6 and RCP8.5 relative to the baseline period 1971 to 2000 obtained from the Coupled Model Inter-comparison Project phase 5 (CMIP5) multi-model ensemble. As a result, it is expected that the lake will further increment in surface area and depth by the year 2100 due to increased rainfall, thereby affecting the populations of the lesser flamingos and phytoplankton, as the physicochemical factors of the lake will alter as well during the projected period.