Narok town is one of the places in Kenya which experience catastrophic floods. Many lives have been lost and valuable property destroyed in recent years. Change in land use/land cover upstream of the ...town area may have contributed significantly to the severity and frequency of flooding events. Runoff, which contributes to floods in Narok town, comes from Kakia and Esamburmbur sub-catchments of Enkare Narok watershed. The objective of this study was to assess the impact of land use/land cover change on the hydrology of Kakia and Esamburmbur sub-watersheds. To detect land use/land cover change, Landsat satellite images from 1985 to 2019 were used. Using supervised classification in Erdas Imagine 2014, land use of the study area was classified into four classes, i.e., forest, rangeland, agriculture and built-up areas. Five land use maps (1985, 1995, 2000, 2010, and 2019) were developed and used to perform land use change analysis. There was rampart conversion of forest to other land uses. Between 1985 and 2019, the forest and rangeland declined by 40.3% and 25.6% of the study area, respectively, while agriculture and built-up areas increased by 55.2% and 10.6% of the study area respectively. Analysis of soil hydrological properties indicate that the infiltration rate and soil hydraulic conductivity were greatest in forest than in other land use types. The basic infiltration rate in forest land was 89.1 cm/h while in rangeland and agricultural land, it was 7.9 cm/h and 15 cm/h respectively. At the top-soil layer, average soil hydraulic conductivity under forest was 46.3 cm/h, under rangeland, 2.6 cm/h and under agriculture, 4.9 cm/h. The low hydraulic conductivity in rangeland and agriculture was attributed to compaction by farm machinery (tractors) and livestock respectively. An interesting observation was made in rangelands where the top layer (0–20 cm) had a higher bulk density and a lower hydraulic conductivity as compared to the next deeper layer (20–40 cm). This was attributed to the combined impact of compaction and localised pressure by hooves of livestock which only have an impact on the top layer. The findings of this study show that land use has a major impact on soil hydrological properties and imply that the observed land use changes negatively affected the soil hydrological properties of the watershed. The decreased infiltration in the increasing areas of degraded land (mainly agriculture and rangeland) and increase in built-up area in Narok town are the possible causes of the increased flood risk in Narok town. It is recommended that flood risk management strategies in Narok town include watershed management to enhance water infiltration.
Functions and services provided by soils play an important role for numerous sustainable development goals involving mainly food supply and environmental health. In many regions of the Earth, water ...erosion is a major threat to soil functions and is mostly related to land-use change or poor agricultural management. Selecting proper soil management practices requires site-specific indicators such as water erosion, which follow a spatio-temporal variation. The aim of this study was to develop monthly soil erosion risk maps for the data-scarce catchment of Ruiru drinking water reservoir located in Kenya. Therefore, the Revised Universal Soil Loss Equation complemented with the cubist–kriging interpolation method was applied. The erodibility map created with digital soil mapping methods (
R
2
= 0.63) revealed that 46% of the soils in the catchment have medium to high erodibility. The monthly erosion rates showed two distinct potential peaks of soil loss over the course of the year, which are consistent with the bimodal rainy season experienced in central Kenya. A higher soil loss of 2.24 t/ha was estimated for long rains (March–May) as compared to 1.68 t/ha for short rains (October–December). Bare land and cropland are the major contributors to soil loss. Furthermore, spatial maps reveal that areas around the indigenous forest on the western and southern parts of the catchment have the highest erosion risk. These detected erosion risks give the potential to develop efficient and timely soil management strategies, thus allowing continued multi-functional use of land within the soil–food–water nexus.
The objective of this study was to analyze patterns, dynamics and processes of land-use/cover changes in the transboundary Mara River Basin in East Africa. We specifically focused on deforestation ...and expansion of agriculture in the watershed. The intensity analysis approach was used to analyze data from satellite imagery-derived land-use/cover maps. Results indicate that swap change accounted for more than 50% of the overall change, which shows a very dynamic landscape transformation. Transition from closed forest to open forest was found to be a dominant landscape change, as opposed to a random change. Similarly, transition from open forest to small-scale agriculture was also found to be a dominant transition. This suggests a trend (pathway) of deforestation from closed forest to small-scale agriculture, with open forest as a transitional land cover. The observed deforestation may be attributed to continuous encroachment and a series of excisions of the forest reserve. Transition from rangeland to mechanized agriculture was found to be a dominant land-use change, which was attributed to change in land tenure. These findings are crucial for designing strategies and integrated watershed management policies to arrest further deforestation in the forest reserves as well as to sustainably control expansion of agriculture.
Study region: Nyangores River watershed, headwater catchment of Mara River basin in Kenya. Study focus: Climate variability and human activities are the main drivers of change of watershed hydrology. ...The contribution of climate variability and land use change to change in streamflow of Nyangores River, was investigated. Mann Kendall and sequential Mann Kendall tests were used to investigate the presence and breakpoint of a trend in discharge data (1965–2007) respectively. The Budyko framework was used to separate the respective contribution of drivers to change in discharge. Future response of the watershed to climate change was predicted using the runoff sensitivity equation developed. New hydrological insights for the region: There was a significant increasing trend in the discharge with a breakpoint in 1977. Land use change was found to be the main driver of change in discharge accounting for 97.5% of the change. Climate variability only caused a net increase of the remaining 2.5% of the change; which was caused by counter impacts on discharge of increase in rainfall (increased discharge by 24%) and increase in potential evapotranspiration (decreased discharge by 21.5%). Climate change was predicted to cause a moderate 16% and 15% increase in streamflow in the next 20 and 50 years respectively. Change in discharge was specifically attributed to deforestation at the headwaters of the watershed. Keywords: Climate variability, Land use change, Hydrology, Streamflow, Water security, Budyko framework
The largest impact of land-use change on catchment hydrology can be linked to deforestation. This change, driven by exponential population growth, intensified food and industrial production, has ...resulted in alterations in river flow regimes such as high peaks, reduced base flows, and silt deposition. To reverse this trend more extensive management practices are becoming increasingly important, but can also lead to severe losses in agricultural production. Land-use optimization tools can help catchment managers to explore numerous land-use configurations for the evaluation of trade-offs amongst various uses. In this study, the Soil and water assessment tool (SWAT) model was coupled with a genetic algorithm to identify land-use/management configurations with minimal trade-offs between environmental objectives (reduced sediment load, increased stream low flow) and the crop yields of maize and soybean in Nyangores catchment (Kenya). During the land-use optimization, areas under conventional agriculture could either remain as they are or change to agroforestry or conservation agriculture (CA), where the latter was represented by introducing contour farming and vegetative filter strips. From the sets of the resulting Pareto-optimal solutions we selected mid-range solutions, representing a fair compromise among all objectives, for further analysis. We found that a combined measure implementation strategy (agroforestry on certain sites and conservation agriculture on other sites within the catchment) proved to be superior over single measure implementation strategies. On the catchment scale, a 3.6% change to forests combined with a 35% change to CA resulted in highly reduced sediment loads (−78%), increased low flow (+14%) and only slightly decreased crop yields (<4%). There was a tendency of the genetic algorithm to implement more extensive management practices in the upper part of the catchment while leaving conventional agriculture in the lower part. Our study shows that a spatially targeted implementation strategy for different conservation management practices can remarkably improve environmental sustainability with only marginal trade-offs in crop production at the catchment-level. Incentive policies such as payments for ecosystem services (PES), considering upstream and downstream stakeholders, could offer a practical way to effect these changes.
•The 5-segment Flow Duration Curve (5FDC) provided a better representation of the low and mid-level section flow.•5FDC method is more suitable for long-term water management.•Normal Calibration ...Procedure (NCP) focused on the flows favored by the objective functions selected for analysis.•The hybrid procedure (CP) merged the strengths exhibited by both the 5FDC and NCP leading to reduced parameter uncertainty•5FDC provides a better representation of the low and mid-level section of the flow duration curve as compared to the NCP.
Nyangores catchment, Mara catchment, Kenya.
Hydrologic models are widely used tools in watershed management to assist in decision making by representing catchment functions under alternative scenarios. This study focused on the evaluation of the 5 segment Flow Duration Curve based calibration procedure (5FDC) for the period 1975–1978 using the Soil Water Assessment Tool (SWAT). The Normal Calibration Procedure (NCP) based on the hydrograph was compared to the 5FDC. Two separate ensembles each containing 10 Pareto calibration runs were obtained individually from each method and evaluated based on their goodness-of-fit. A final Combined Procedure (CP), which was an intersection of 5FDC and NCP was executed. With this supplementary analysis, the parameter distribution and water component balance were analyzed and compared.
The comparison of 5FDC and NCP shows that the 5FDC provides a better representation of the low and mid-level section of the flow duration curve as compared to the NCP, which greatly overestimates these flows. This method also closely matches the observed runoff ratios. This indicates that the 5FDC calibration may be well suited for water resource applications focused on low flows. The CP combines the advantages of both procedures by improving parameter identifiability, leading to better representation of high and low flows.
This research presents a comprehensive study on water resources in the semi-arid regions of Isiolo and Samburu counties in Kenya, with a focus on the conservancies. The study employed a ...multidisciplinary approach to evaluate water availability, accessibility, quality, and suitability for improved livelihoods in these regions. Data was collected through literature reviews, site visits, and laboratory experiments, with a specific focus on groundwater and surface water sources. Our study revealed that the primary source of domestic water was from boreholes. They had an average depth of approximately 70 m, with average yields of 2 to 6 m3/hr and were strategically located along the riparian areas of Laggas, which are fairly fractured, allowing for recharge of floodwater. Some areas had poor groundwater yields of 1- 2 m3/hr which could be attributed to the hard geological formations and limited recharge areas within the region. The areas geological composition comprises of volcanic layers of basalts, trachytes, phonolites overlain by regolith, which retain water except the basalts and trachytes have limited water storage capacity resulting into poor yields when fractured. There was a diversification of water resource use including; water pans, springs, rivers, boreholes, earth dams, rock catchment and gravity water supply to curb seasonality. The TDS, pH, dissolved oxygen (DO), and electrical conductivity (EC) were within the WHO recommended standards except for variations such as high alkalinity, high fluoride levels, and excess algae observed especially in the water pans indicating the presence of pollution. Identified challenges included: construction and design problems, improper siting, siltation, lack of protection, absence of spillways and silt traps, and contamination by livestock and wildlife. The research highlights the significance of diversified water sources, alternative energy solutions, groundwater potential, and community-based management for addressing water scarcity and improving access to clean and safe water for arid livelihoods sustainability.
Water erosion results in sedimentation, which reduces storage capacities in reservoirs and lowers their productive life. To effectively develop strategies for the mitigation of reservoir ...sedimentation, an assessment of the spatial variation of erosion is necessary. In data-scarce areas, soil erosion proxies such as aggregate stability can be used to map erosion hotspots. To assess the potential of using aggregate stability as a proxy for soil erosion, 90 sampling sites in the Ruiru catchment (Kenya) were selected using conditioned latin hypercube-based sampling. Aggregate stabilities were determined based on mean weight diameter (MWD). Thereafter, digital soil mapping (DSM) of MWD was applied to identify erosion-prone areas. Correlation analysis between MWD, soil properties and covariates revealed that organic carbon had the highest influence (27.9%) on MWD. When comparing the MWDs under different land-uses, areas under cropland and tea plantations had lower MWDs (2.54 ± 0.39 mm and 2.83 ± 0.36 mm, respectively) than forested areas (3.18 ± 0.09 mm) and were more susceptible to aggregate breakdown. A spatial map created using DSM revealed that earthen roadsides had the lowest MWD of 2.07 ± 0.27 mm; thus, highlighting their potential role in contributing to erosion. From our findings, the prediction of aggregate stability appears to be a valuable resource tool to identify erosion ‘hotspots’ and might be used for the development of catchment management plans aiming at mitigation of soil degradation.
•Soil proxies such as aggregate stability can be used to identify erosion hotspots.•Soil samples are collected using the conditioned Latin Hypercube sampling.•Digital soil mapping on aggregate stability is done by applying cubist model with regression kriging.•Organic carbon has the highest influence on aggregate stability.•Lowest and highest Mean Weight Diameters are on roadsides and forests respectively.
Climate change and land use change are two forces influencing the hydrology of watersheds and their ability to provide ecosystem services, such as clean and well-regulated streamflow and control of ...soil erosion and sediment yield. The Soil Water Assessment Tool, SWAT, a distributed, watershed-scale hydrological model was used with 18 scenarios of rainfall, temperature and infiltration capacity of land surface to investigate the spatial distribution of watershed services over the 3587 km2 Nyando basin in Western Kenya and how it is affected by these two forces. The total annual water yield varied over the 50 sub-basins from 35 to 600 mm while the annual sediment yield ranged from 0 to 104 tons ha−1. Temperature change had a relatively minor effect on streamflow and sediment yield compared to change in rainfall and land surface condition. Improvements in land surface condition that result in higher infiltration are an effective adaptation strategy to moderate the effects of climate change on supply of watershed services. Spatial heterogeneity in response to climate and land use change is large, and hence it is necessary to understand it if interventions to modify hydrology or adapt to climate change are to be effective.
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