Establishing the Relationship Between Lulc Changes, Temperature, Precipitation and Water Level Rise: Case Study of Lake Nakuru Basin, Kenya.

Abstract

Kenya’s Rift Valley lakes have been rising at an alarming rate since the occurrence of the El Nino event in (1997-1998) leading to flooding. These floods have posed a significant threat to the region's socioeconomic progress. Homes, schools, transport network, wildlife habitats, and places of worship among others have been submerged and destroyed leading to displacement of several thousands of people and wildlife. The presence of sediment on the roads and rivers within the catchment clearly shows that increased human activities has led to increased soil erosion which has contributed to the lake siltation that has led to the rising water level in the rift valley lakes. An active tectonic belt, climate change, and increased human activity in the lake basin are all probable causes of the water level rise. However, for this study only LULC changes, temperature and precipitation will be considered. The main objective of this research was to establish whether LULC changes, temperature and precipitation have an effect on the water level rise. To achieve the first objective, Google Earth Images between 1990 to 2020 were digitized to produce the lake horizontal extent while the 12.5m DEM was used to generate 2m interval contour lines. The horizontal extent and the contour lines were overlaid and contours lines that were found to be along the horizontal extent were selected to represent the vertical extent of the lake for the four years. For the second objective, a correlation coefficient matrix between LULC changes, temperature, precipitation and the rising water level was done to establish their relationship. Landsat Images between 1990 to 2020 were pre-processed, and classified into seven LULC classes (forests, water bodies, grasslands, settlements, agriculture, barelands and shrubs) using maximum likelihood supervised classification. For the third objective, select within a source feature method was used to identify infrastructure affected. The results show that the vertical extent of the lake has increased by 9 metres from 1759 m in 1990 to 1768 m in 2020, horizontally the lake extent has increased from 35.60 Km2 in 1990 to 67.07 Km2 in 2020 which is a 31.47 Km2 (88.4%) increase. With reference to the second objective, it was found out that there is a relation between LULC changes, temperature, precipitation and the water level rise in the lake. There is a very strong positive correlation (Corr = 0.964327) between precipitation and water level rise. These makes precipitation the main probable cause of water level rise in Lake Nakuru, among other probable causes. Built-up areas have increased from 17.35 Km2 in 1990 to 99.71 Km2 in 2020 (474%). However, forest cover has been decreasing from 376.52 Km2 in 1990 to 154.53 Km2 in 2020 (59.04%). Annual mean precipitation has increased by 950% from 826.79 mm in 1990 to 2020 mm in 2020, with the massive increase taking place between the year 2010 and 2020. The annual average temperatures have also increased from 23.370C in 1990 to 240C in 2020. In terms of the infrastructure affected, 178 building structures, 4 Road networks and one powerline have been submerged and destroyed. The study, recommends that a research considering all probable cause of the lake level rise be done using a much higher resolution DEM and Images for more accurate results. We also recommend that a research to identify the most appropriate contour line to be used to create riparian zone along the lake be done.