Alfred Opere

Holocene palaeohydrology, groundwater and climate change in the lake basins of the Central Kenya Rift

Abstract The Central Kenya Rift contains small soda lakes such as Nakuru, Elmenteita and Bogoria, freshwater Lake Naivasha, and the partly (spatially) freshwater Lake Baringo. The hydrology of this area is controlled mainly by climate, tectonically controlled morphological and volcanic barriers, faults, and local water-table variations. Much of the area relies on groundwater for human and industrial use, though there are widespread quality issues particularly in relation to fluoride. Despite the huge demand for the resource, little is known about the highly complex groundwater systems; lacking monitoring data, an assessment is developed on the basis of regional geological, hydrogeological and hydrochemical analyses. Significant hydrological changes have taken place in the region over the last 10 000 years as a result of global, regional and local changes, but the impacts on groundwater resources are still largely unknown. The IPCC projects a 10–15% increase of rainfall in the area, but it may not necessarily result in a proportional increase in groundwater recharge. High groundwater recharge periods appear to be anchored on a decadal cycle.

Plant parasitic nematode assemblages associated with sweet potato in Kenya and their relationship with environmental variables

Sweet potato is one of the most important staple food crops consumed in Kenya and throughout Africa but yields are greatly reduced by plant parasitic nematodes (PPN). The aim of this study was to determine the prevalence of PPN in Kenyan sweet potato fields and their relationship with soil and climatic variables. Soil samples were collected from sweet potato fields in Busia, Teso, Kisii, Embu and Makueni counties. Thirteen nematode genera were identified across the five counties with Meloidogyne, Pratylenchus and Rotylenchus being the most prevalent. There was a significant (P <0.05) relationship between PPN abundance and sodium, calcium and iron. Canonical correspondence analysis of climatic variables revealed that the relationship between rainfall and nematode genera was significant (P <0.05) while maximum and minimum temperatures were not significant. This description of PPN assemblages associated with sweet potato in Kenya and their relationship with environmental variables provides a starting point from which appropriate nematode management strategies can be implemented.

Hydrological Response and Complex Impact Pathways of the 2015/2016 El Niño in Eastern and Southern Africa

The 2015/2016 El Nino has been classified as one of the three most severe on record. El Nino teleconnections are commonly associated with droughts in southern Africa and high precipitation in eastern Africa. Despite their relatively frequent occurrence, evidence for their hydrological effects and impacts beyond agriculture is limited. We examine the hydrological response and impact pathways of the 2015/2016 El Nino in eastern and southern Africa, focusing on Botswana, Kenya, and Zambia. We use in situ and remotely sensed time series of precipitation, river flow, and lake levels complemented by qualitative insights from interviews with key organizations in each country about awareness, impacts, and responses. Our results show that drought conditions prevailed in large parts of southern Africa, reducing runoff and contributing to unusually low lake levels in Botswana and Zambia. Key informants characterized this El Nino through record high temperatures and water supply disruption in Botswana and through hydroelectric load shedding in Zambia. Warnings of flood risk in Kenya were pronounced, but the El Nino teleconnection did not materialize as expected in 2015/2016. Extreme precipitation was limited and caused localized impacts. The hydrological impacts in southern Africa were severe and complex, strongly exacerbated by dry antecedent conditions, recent changes in exposure and sensitivity and management decisions. Improved understanding of hydrological responses and the complexity of differing impact pathways can support design of more adaptive, region-specific management strategies.

Hydrological Characteristics of Lower Nzoia Sub-basin in Kenya

This study sought to investigate hydrological characteristics of lower Nzoia sub-basin in Kenya. Trend (long and medium) utilized graphical and statistical approach. Extreme value (EV) analysis based on frequency, annual maximum flows, exceedance probability, low flows and probable maximum precipitation was used. Quality control showed consistency in rainfall, temperature and discharge datasets. Maximum-minimum monthly and annual flows and rainfall showed maximum flows centered in March-to-May (peak) with increasing temperature. Trends, seasonality and cycles were identified and maximum values in rainfall and discharge closely followed the pattern for peak rainfall seasons. Based on the flow magnitudes and 100-year return period, the upstream station (1EE01) had lower values compared to downstream station (1EF01) for different assumed distributions and thus 1EF01 assumed to be more reliable. Exponential and Pareto distributions indicated a normal tail and thus appropriateness of EV1/Gumbel distribution in calibrating AM series. Best conventional calibration results based on assumed distributions using EV1/Gumbel superimposed with the extreme value distribution fitted along with the exponential/Pareto Q-Q plots for comparison. Estimated maximum withdrawal in monthly terms for 1EE01 and 1EF01 was 262.5 and 368.4 cumecs respectively. Analyses of low stream flow indicate probable availability of water in streams at different return periods.

Chapter 21 – Floods in Kenya

Abstract The vulnerability of a water resource system to climate change is a function of a number of physical features and social characteristics. The physical features associated with maximum vulnerability of water resources in a region include the marginal hydrologic and climatic regime; high rates of sedimentation leading to reduction of reservoir storage; topography and land-use practices that promote soil erosion and flash flooding conditions; and deforestation, which allows increased surface run-off, increased soil erosion and more frequent significant flooding. Coupled with these factors, the social characteristics that increase vulnerability of water resources include poverty and low income levels that prevent long-term planning and provision at the household level, lack of water control infrastructures, inadequate maintenance and deterioration of existing infrastructure, lack of human capital skills for system planning and management, lack of appropriate and empowered institutions, absence of appropriate land-use planning and management, and high population densities and other factors that inhibit population mobility. Of all the relevant factors in climate, precipitation is the main cause of disasters in flooding, water pollution, soil erosion, dam breaks and water-related disease outbreaks among others. Floods increase vulnerability of society and thereby perpetuate and increase the incidence of poverty.