How climate and land use determine the hydrology of Lake Naivasha Basin

Abstract

Recent hydro-climatological trends and variability characteristics were investigated for the Lake Naivasha Basin with the aim of understanding the changes in water balance components and their evolution over the past 50 years. Using Bayesian change point analysis proposed by Barry and Hartigan (1993) and modified Mann-Kendall tests time series of annual mean, maximum, minimum, and seasonal precipitation and flow, as well as annual mean lake volumes were analyzed for the period 1960-2010 to uncover possible abrupt shifts and gradual trends. Double cumulative curve analysis was used to investigate changes in hydrological response attributable to either human influence or climatic variability. The results indicate a significant decline in lake volumes at a mean rate of 9.35×10 6 m 3 year-1. Most of the river gauging stations showed no evidence of trends in the annual mean and maximum flows as well as seasonal flows. Annual minimum flows, however, showed abrupt shifts and significant (upward/downward) trends at the main outlet stations. Precipitation in the basin showed no evidence of abrupt shifts, but a few stations showed gradual decline. The observed changes in precipitation could not explain the decline in both minimum flows and lake volumes. The findings show no evidence of any impact of climate change for the Lake Naivasha basin over the past 50 years. This implies that other factors, such as changes in land cover and infrastructure development, have been responsible for the observed changes in stream flow and lake volumes.

Assessment of Rainfall, Streamflow and Reservoir Level Trends for Malewa River Catchment, Naivasha, Kenya

“…When there are no trends, the observed data obtained over time (years or months) were independently and identically distributed. Therefore, no general trend of rainfall for the previous periods [19].…”

“…The years 1981The years , 2001The years , 2003The years , 2012The years and 2018The years indicated an increasing trend while 1980The years , 1982The years , 1984The years , 1986The years , 1987The years , 2000The years , 2004The years , 2008The years and 2014 showed a decreasing trend as the results were statistically significant using P-values. As shown by the graph, the reservoir level regularly had a downward trend up to 2008 which closely matches the finding presented by Odongo., Reta., Awange., Boitt [19][20][21][22]. However, the water level in the Lake from 2009 had an upward trend except 2014 and 2017 as shown in Figure 7.…”

Evaluation of Spatial and Temporal Hydrological Drought Using Surface Water Supply Index in Malewa River Catchment, Naivasha

“…The local reliefs in the catchment are Aberdare Mountain in the East and Mau Escarpment to the West makes the area have two rainy seasons (Odongo, 2016). The long rain occurs between March to May while the short rain occurs between October and November with its average annual rainfall ranging between 1525 to 610 mm (Kyambia & Mutua, 2014).…”

“…Acute drought conditions had greatly affected Africa and East Africa region where 2011-2012, 11 million people encountered famine and mass displacement. Also, in the year 2015-2016, Northern Ethiopia and 2016-2017 Greater Horn of Africa, were seriously hit by drought (Kilavi et al, 2018). The Government of Kenya declared a national drought in 2017 which had affected 2.7 million people (Koehler, 2018).…”

Hydroclimatic Analysis of Rising Water Levels in the Great Rift Valley Lakes of Kenya

“…For Lake Naivasha, where a long-term mean ratio of AET to rainfall of 0.72 results in a runoff coefficient rc of 0.28 for the ERA5L-data, Ayenew et al, (2007) used a value of 0.13 for rc. For the same lake, Odongo (2016) published mean rc values of 0.2 -0.25. Muthuwatta (2014) evaluated runoff and precipitation data for a single year (1971) for Lake Naivasha tributaries and found very low rc values of 8.5% at Gilgil and 3.5% for the Malewa subbasin.…”