This paper reports on the energy balance and partitioning analysed from 3-year micrometeorological flux measurements of energy and water fluxes over a heterogeneous semi-arid shrubland ecosystem in Lake Naivasha basin. The measurements enabled the characterization of the seasonal and interannual variability of the energy and water fluxes of the ecosystem covering two wet years (2012 and 2013) and one drought year (2014). On an annual scale, more than 60% of net radiation (Rn) was partitioned as latent (LE) and sensible (H) energy flux, with the latter being the larger consumer of Rn (similar to 34%) and dominant for most months. The transition from H to LE dominance occurred from early noon to late afternoon in the wettest months of April and May. The residual energy balance closure term (C) accounted for between 25 and 40% of the Rn with the imbalance tending to be highest during periods of high insolation. Annual evapotranspiration was estimated at 873 mm, 632mm and 537mm for year 2012, 2013 and 2014 respectively. This accounted for at least 80% of the annual precipitation received for the respective years. Surface conductance (g(s)) scaled significantly with leaf expansion and Priestley-Taylor alpha coefficient, but was limited during periods of drought because of inadequate soil moisture suggesting that, change in LE was paralleled by changes in green leaf area index. Low values of decoupling coefficient (Omega) during these periods indicated that evapotranspiration was strongly controlled by g(s) and vapour pressure deficit (VPD). However, under non-limiting moisture conditions evapotranspiration was decoupled from the atmosphere. This suggested that during the dry seasons and periods of prolonged drought, a lack of moisture in combination with high VPD leads to significant decreases in stomatal conductance that eventually limits partitioning of available energy into LE in the semi-arid ecosystem part of the Lake Naivasha basin. However, during wet season these factors are non-limiting and radiation is the dominant control of energy partitioning into LE in the ecosystem. The coupling and decoupling pattern provide insights towards formulating models that quantify evapotranspiration for ecosystems that experience seasonal shifts in controlling factors. Copyright (C) 2016 John Wiley & Sons, Ltd.

Lake Naivasha was designated as a RAMSAR site in 1995. The lake environment is fragile and critically threatened by human-induced factors. The study presented a steady and transient numerical modeling. The long-term and system flux over time interaction between the lake and the surficial aquifer is represented in the Lake Package LAK3 with in the advanced 3-D simulation sofware (GMS). The model covers an area of 1817 km 2 . Model calibration was constrained by the observed groundwater and lake levels using PEST. The effect of excessive abstraction was rigorously analyzed via scenario analysis. The simulation was evaluated “with abstraction” and “without abstraction” scenarios. The abstraction scenario was simulated using range of combination assuming that all the abstraction was from the lake or the groundwater and in the ratio of groundwater and lake water. The effect of the stress was evaluated based on the observed aquifer heads and lake stage at the end of the simulation time. The development of low groundwater-level anomalies in the well field is explained. The result indicates that the one of the well fields is not in direct hydraulic connection to the main recharging water body. Apparently, similar development of cone of depression was not generated in the other two well fields, and this could have several reasons including due to the fact that these well fields are located relatively close by to the main recharging zones and concluded to have additional source of recharge, and this was supported by previous studies, whereby the isotopic composition of the boreholes has their source of recharge from precipitation and river and was also confirmed from the isotopic composition of unsaturated zone, which is a mixture of river and rain. The study reveals that seasonal variability of groundwater–surface water exchange fluxes and its spatially and temporally variable impact substantially on the water resource availability. Such analysis can be used as a basis to quantify the linkages between the surface water and groundwater regime and impacts in the basin. The model output is expected to serve as a basis via linking/coupling with others to incorporate the ecology and biodiversity of the lake to safeguard this high-value world heritage water feature.

Effective integrated water resources management requires reliable estimation of an overall basin water budget and of hydrologic fluctuations between groundwater and surface-water resources. Seasonal variability of groundwater-surface water exchange fluxes impacts on the water balance. The long term lake water balance was calculated by Modflow using the stage-volume rating curve of Lake Package LAK3. The long term average storage volume change is 8.4 x 10(8) m(3)/month. The lake water balances suggests that the lake is not in equilibrium with the inflow and outflow terms. Using field abstraction data analysis and model simulation, the combined volume of lake-groundwater used for industrial abstraction since the last three decades was estimated. This requires an average abstraction amount of 7.0x 10(6) m(3)/month with a long term trend of abstraction ratio 30% (groundwater) and 70% (lake water) since 1980. The amount resulted in a lake which might have been 4.8 m higher than was observed in the last stress period (2010). A long term regional groundwater budget is calculated reflecting all water flow in to and out of the regional aquifer. The model water balance suggests that lake Navaisha basin is in equilibrium with a net outflow about 1% greater than the inflow over the calibrated period of time (1932-2010). The regional model is best used for broad-scale predictions and can be used to provide a general sense of groundwater to surface water and groundwater to groundwater impacts in the basin. Abasin wide water resource management strategy can be designed by integrating the lake/wetland within the regional groundwater model to increase the level of sustainable production and good stewardship in Lake Navaisha. Such hydrological analysis is crucial in making the model serve as simulator of the response of lake stage to hydraulic stresses applied to the aquifer and variation in climatic condition.

In 2009 Kenya was hit by a severe drought which reduced the available water resources, thus impacting citizens and industry alike. In particular, Lake Naivasha receded to its lowest level in 75 years. The area around the lake had seen steady growth of the population and the flower industry, increasing the burden on the water resources. To address the situation a combined effort by the government, civil society and the private sector was launched which resulted in the Integrated Water Resource Action Plan Programme. Modern geospatial technologies and open-source software allow efficient system development to support the implementation of this programme.

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 50years. Using a Bayesian change point analysis 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 analysed for the period 1960-2010 to uncover possible abrupt shifts and gradual trends. Double cumulative curve analysis was used to investigate the 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 9.35x10(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 50years. This implies that other factors, such as changes in land cover and infrastructure development, have been responsible for the observed changes in streamflow and lake volumes. Copyright (c) 2015 John Wiley & Sons, Ltd.

Most hydrological studies do not account for the socio-economic influences on eco-hydrological processes. However, socio-economic developments often change the water balance substantially and are highly relevant in understanding changes in hydrological responses. In this study a multi-disciplinary approach was used to study the cascading impacts of socio-economic drivers of land use and land cover (LULC) changes on the eco-hydrological regime of the Lake Naivasha Basin. The basin has recently experienced substantial LULC changes exacerbated by socio-economic drivers. The simplified cascade models provided insights for an improved understanding of the socio-ecohydrological system. Results show that the upstream population has transformed LULC such that runoff during the period 1986-2010 was 32% higher than during the period 1961-1985. Cut-flower export volumes and downstream population growth explain 71% of the water abstracted from Lake Naivasha. The influence of upstream population on LULC and upstream hydrological processes explained 59% and 30% of the variance in lake storage volumes and sediment yield respectively. The downstream LULC changes had significant impact on large wild herbivore mammal species on the fringe zone of the lake. This study shows that, in cases where observed socio-economic developments are substantial, the use of a cascade-modeling approach, that couple socio-economic factors to eco-hydrological processes, can greatly improve our understanding of the eco-hydrological processes of a catchment. (C) 2014 Elsevier B.V. All rights reserved.

A conceptual flash flood early warning system for developing countries is described. The system uses rainfall intensity data from terrestrial microwave communication links and the geostationary Meteosat Second Generation satellite, i.e., two systems that are already in place and operational. Flash flood early warnings are based on a combination of the Flash Flood Guidance method and a hydrological model. The system will be maintained and operated through a public-private partnership, which includes a mobile telephone operator, a national meteorological service and an emergency relief service. The mobile telephone operator acts as both the supplier of raw input data and the disseminator of early warnings. The early warning system could significantly reduce the number of fatalities due to flash floods, improve the efficiency of disaster risk reduction efforts and play an important role in strengthening the resilience to climate change of developing countries in Africa. This paper describes the system that is currently being developed for Kenya.

This study discusses the effects of water abstractions from two alternative sources on the available water volume around Lake Naivasha, Kenya: the lake itself and a connected aquifer. An estimation of the water abstraction pattern for the period 1999–2010 is made and its effect on the available water volume in Lake Naivasha and its connected aquifer is evaluated using a simple water balance modeling approach. This study shows that accurate estimates of annual volume changes of Lake Naivasha can be made using a simple monthly water balance approach that takes into account the exchange of water between the lake and its connected aquifer. The amount of water that is used for irrigation in the area around Lake Naivasha has a substantial adverse effect on the availability of water. Simulation results of our simple water balance model suggests that abstractions from groundwater affect the lake volume less than direct abstractions from the lake. Groundwater volumes, in contrast, are much more affected by groundwater abstractions and therefore lead to much lower groundwater levels. Moreover, when groundwater is used instead of surface water, evaporation losses from the lake are potentially higher due to a larger lake surface area. If that would be the case then the overall water availability in the area is more strongly affected by the abstraction of groundwater than by the abstraction of surface water. Therefore water managers should be cautious when using lake levels as the only indicator of water availability for restricting water abstractions.

Lake Naivasha experiences frequent lake level fluctuations despite being on the decline in the last three decades. The main possible cause has been postulated to be increased abstraction around the lake. However, land use land cover changes (LULC) in the basin may be impacting on the level fluctuations and decline. The LULC interfere with runoff, evapotranspiration, and infiltration conditions of a catchment. The frequent lake levels fluctuations resulting from LULC impact significantly on riparian vegetation productivity and species composition. In addition, it has impact on the aquatic ecosystem water quality especially in terms of turbidity. Lake Naivasha basin has experienced significant LULC transformations predominantly caused by socio-economic drivers. Implications of past, present and future patterns of socio-economic drivers of LULC is vital to the understanding of social, ecological and limnological functioning of the basin. These factors are proposed to impact on the entire hydrological regime of the lake. In this study we present first results of the Earth Observation Integrated Assessment (EOIA) project for the governance of Lake Naivasha basin using Interdisciplinary approach that applies GIS and RS towards the understanding of the dynamics of Lake Naivasha ecosystem.

Aquifers near Lake Naivasha, Kenya are important water resources and are used extensively for irrigation and for municipal and domestic water supplies. Head data for a 79-year period (1932-2010) were analyzed to develop a conceptual model of aquifer-lake interaction and used to develop a three-dimensional numerical model. A three-dimensional groundwater flow model with four layers was used to simulate ground-water flow in the aquifers and lake-aquifer interaction. The lake is simulated by specifying a high hydraulic conductivity for lake-volume grid cells. The 90 m Digital Elevation Model (DEM) that includes the bathymetry improved the 3-D representation of the lake in the groundwater system and helped to define the deformed layer that honors the stratigraphy. The calibration process was carried out using PEST in conjunction with pilot points and regularization. The finite difference groundwater model results were comparable with measured head data and isotopic and hydro-chemical data. The sensitivity of the computed lake level was tested using the "high-K" method to the choice of K2/K1, where K2 and K1 are the hydraulic conductivity of the lake node and the aquifer (respectively). Higher values of K2/K1 should be used with higher regional gradients on the order of 0.002 to ensure mainly accurate calculations of seepage rates to and from the lake. (C) 2013 Elsevier B.V. All rights reserved.

Simulation models are widely used for studying physical processes such as surface runoff, sediment transport and sediment yield in catchments. Most models need case-specific empirical data for parameterization before being applied especially in regions other than the ones they have been developed. Sensitivity analysis is usually performed to determine the most influential factors of a model so that they can be prioritized for optimization. In this way uncertainties in model outputs can be reduced considerably. This study evaluates the commonly used modified universal soil loss equation (MUSLE) model used for sediment yield simulation for the case of the upper Malewa catchment in Kenya. The conceptual factors of the model are assessed relative to the hydrological factors in the model. Also, the sensitivity of the model to the choice of the objective function in calibration is tested. The Sobol' sensitivity analysis method was used for evaluating the degree of sensitivity of the conceptual and hydrological factors for sediment yield simulations using the MUSLE model. Nash-Sutcliffe Efficiency (NSE) and the modified Nash-Sutcliffe Efficiency (NSEm) are used to test the sensitivity of the model to the choice of the objective function and robustness of model performance with sediment data measured from upper Malewa catchment, Kenya. The results indicate that the conceptual factors are the most sensitive factors of the MUSLE model contributing about 66% of the variability in the output sediment yield. Increased variability of sediment yield output was also observed. This was attributed to interactions of input factors. For the upper Malewa catchment calibration of the MUSLE model indicates that the use of NSEm as an objective function provides stable results, which indicates that the model can satisfactorily be applied for sediment yield simulations.

Remotely-sensed data can be used to overcome deficiencies in data availability in poorly monitored regions. Reliable estimates of human population densities at different spatial levels are often lacking in developing countries. This study explores the applicability of a geographically-weighted regression (GWR) model for estimating population densities in rural Africa using land use/cover data that have been derived from remote-sensing while accounting for spatial non-stationarity. This study was conducted for the Lake Naivasha basin in Kenya where population pressure, intense land utilization in the catchment and informal settlements in Naivasha town due to lucrative economic activities are the major challenges of the basin socio-ecological system. The results of this study show that using a GWR model for taking into account the spatially-varying relationship between specific land use/cover classes and population significantly improves population estimates and handles the spatial non-stationarity that could not be addressed by global ordinary least squares (OLS) model. The result revealed that the parameter estimates (coefficients) for grassland and cropland use/cover have a significant spatially varying relationship with population and exhibit locally different signs, which would have gone undetected by a global model. Consequently, this study indicates that incorporating spatial non-stationarity can significantly improve population density estimates for rural Africa based on remotely-sensed data.

Kenya's cut-flower industry has been praised as an economic success as it contributed an annual average of US$ 141 million foreign exchange (7 % of Kenyan export value) over the period 1996–2005 and about US$ 352 million in 2005 alone. The industry also provides employment, income and infrastructure such as schools and hospitals for a large population around Lake Naivasha. On the other hand, the commercial farms have been blamed for causing a drop in the lake level, polluting the lake and for possibly affecting the lake's biodiversity. The objective of this study is to quantify the water footprint within the Lake Naivasha Basin related to cut flowers and analyse the possibility to mitigate this footprint by involving cut-flower traders, retailers and consumers overseas. The water footprint of one rose flower is estimated to be 7–13 litres. The total virtual water export related to export of cut flowers from the Lake Naivasha Basin was 16 Mm3/yr during the period 1996–2005 (22 % green water; 45 % blue water; 33 % grey water). Our findings show that, although the decline in the lake level can be attributed mainly to the commercial farms around the lake, both the commercial farms and the smallholder farms in the upper catchment are responsible for the lake pollution due to nutrient load. The observed decline in the lake level and deterioration of the lake's biodiversity calls for sustainable management of the basin through pricing water at its full cost and other regulatory measures. Pricing water at full marginal cost is important, but the conditions in Kenya are unlikely to result in serious steps to full-cost pricing, since many farmers resist even modest water price increases and government is lacking means of enforcement. We propose an alternative in this study that can be implemented with a focus on sustainable water use in flower farming around Lake Naivasha alone. The proposal involves a water-sustainability agreement between major agents along the cut-flower supply chain and includes a premium to the final product at the retailer end of the supply chain. Such a 'water sustainability premium' will raise awareness among flower consumers and—when channelled back to the farmers—facilitate the flower farms to install the necessary equipment and implement the right measures to use water in a sustainable manner. The collected premiums will generate a fund that can be used for financing measures to reduce the water footprint and to improve watershed management.

Several innovative 'participatory sensing' initiatives are under way in East Africa. They can be seen as local manifestations of the global notion of Digital Earth. The initiatives aim to amplify the voice of ordinary citizens, improve citizens' capacity to directly influence public service delivery and hold local government accountable. The popularity of these innovations is, among other things, a local reaction to the partial failure of the millennium development goals (MDGs) to deliver accurate statistics on public services in Africa. Empowered citizens, with access to standard mobile phones, can 'sense' via text messages and report failures in the delivery of local government services. The public disclosure of these reports on the web and other mass media may pressure local authorities to take remedial action. In this paper, we outline the potential and research challenges of a 'participatory sensing' platform, which we call a 'human sensor web.' Digital Africa's first priority could be to harness continent-wide and national data as well as local information resources, collected by citizens, in order to monitor, measure and forecast MDGs.

Inadequate water resources management and a general decline in rainfall have aggravated water scarcity problems in the Upper Ewaso Ng’iro North Basin in Kenya. Furthermore, water use conflicts in the basin have escalated in recent decades due to increased competition for available water resources. Excessive abstraction of the declining river water mainly for irrigation in the Mount Kenya and Nyandarua foot zones often leads to reduced water flow during the dry seasons, greatly affecting downstream water users. Increased water use in the basin coupled with deterioration of the vegetative cover has resulted in reduced water flows in the Ewaso Ng’iro river and its major tributaries. In addition, lack of sufficient knowledge about available water resources and current lack of coordination in water resources management in the basin often result in water deficits which have hampered development in the downstream catchment. The goal of this study was to match the water requirements of various competing sectors in the basin with the available water resources in order to attain both economic and ecological sustainability. To achieve this, GIS techniques were used to quantify the spatial and temporal stream flow. The Water Evaluation and Planning (WEAP) model was applied to evaluate water resources development based on an equilibrium scenario of the current water demand. Water use was simulated for five different sectors (domestic, livestock, wildlife, irrigation and reserve). The analyses revealed that high water demand for irrigation was the main cause of excessive water abstraction particularly in the upstream catchments, giving rise to water shortages and consequently, water use conflicts downstream. The study, therefore, recommends that rainwater harvesting be promoted in the basin in order to improve water availability for productive use.

AbstractThe study area is part of the East African Rift system, characterized by a cluster of lakes occupying an extremely faulted rift floor with geothermal manifestations. Some of the lakes illustrated contrasting water levels and size evolution over the last few decennia, believed to have been caused by various natural and anthropogenic factors. The relative importance of these factors, however, is unknown. This study attempts to present the hydrology of the lakes in a broader context, by giving more emphasis to lake water level fluctuations and to the water balance. These factors have far‐reaching implications in regard to future management of the lake basin water. It also provides information on the relation of the groundwater with the lakes, and with the local and regional groundwater flow system from the adjacent highlands to the floor of the Rift. The methods utilized in this study include conventional hydrogeological field surveys, and hydrometeorological and data analyses, coupled with digital image processing and spatial analysis under a Geographic Information System environment. Ancillary supporting information has been obtained from environmental isotopes and hydrochemical data. The study results indicate the terminal Ethiopian lakes changed in size and water level significantly over the last half century. In contrast, the Kenyan lakes only exhibited slight changes. The lakes in both countries exhibit a striking similarity in their subsurface hydraulic connection, and are strongly governed by complex rift geological structures. Groundwater plays a vital role in the water balance of the study lakes. The study results indicate that future sustainable use of the study lakes demands that serious attention be given to the role of the groundwater component of the lake water balances.