Productivity driven by Tana river discharge is spatially limited in Kenyan coastal waters

The Tana River is the longest river system in Kenya (~1000 km) and contributes ~ 50% of the total river discharge to Kenyan coastal waters. The river discharges significant amounts of nutrients and sediments, reaching ~24,000 tons per day during the rainy season (March–April), into Ungwana Bay (North Kenya Banks). The bay is an important habitat for high-value Panaeid prawn species which sustain important small-scale fisheries, semi-industrial bottom trawl prawn fisheries, and is the livelihood mainstay in the surrounding counties. In this study we analysed >20 years of satellite-derived chlorophyll-a observations (Chl-a, an index of phytoplankton biomass), along with in situ river discharge and rainfall data, to investigate if the Tana River discharge is a major driver of local phytoplankton biomass in Ungwana Bay and for the neighbouring Kenyan shelf. We find that during the rainy inter-monsoon (March–April), a significant positive relationship (r = 0.63, p < 0.0001) exists between river discharge and phytoplankton biomass. There is a clear time-lag between rainfall, river discharge (1-month lag) and local chlorophyll biomass (2-months lag after discharge). Unlike offshore waters which exhibit bi-annual chl-a peaks (0.22 mg m−3 in February, and 0.223 mg m−3 in August/September), Ungwana Bay displays a single peak per annum in July (2.51 mg m−3), with indications that river discharge sustains phytoplankton biomass for several months. Satellite-derived observations and Lagrangian tracking simulations indicate that higher Chl-a concentrations remain locally within the bay, rather than influencing the broader open waters of the North Kenya Banks that are mainly impacted by the wider oceanic circulation

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Power-line sparking noise characterisation in the SKA environment

Thesis (PhD)--University of Stellenbosch, 2011.ENGLISH ABSTRACT: The Square Kilometre Array (SKA) and its demonstrator MeerKAT are being designed to operate over a wide frequency range and are expected to achieve greater sensitivity and resolution than existing telescopes. The radio astronomy community is well aware of the negative impact that radio frequency interference (RFI) has on observations in the proposed frequency band. This is because weak radio signals such as those from pulsars and distant galaxies are difficult to detect on their own. The presence of RFI sources in the telescope’s operating area can severely corrupt observation data, leading to inaccurate or misleading results. Power-line interference and radiation from electric fences are examples of RFI sources. Mitigation techniques for these interference sources in the SKA system’s electromagnetic environment are essential to ensure the success of this project. These techniques can be achieved with appropriate understanding of the characteristics of the noise sources. Overhead power-line interference is known to be caused mainly by corona and gap-type (commonly known as sparking noise) discharges. Sparking noise is the dominant interference for the SKA. It is mainly encountered on wooden pole lines, which are usually distribution lines operated at up to 66 kV AC in the South African network. At this voltage level, the voltage gradients on the lines are insufficient to generate conductor corona. The power requirements for SKA precursors will be below this voltage level. The aim of the research in this dissertation is to evaluate the power line sparking characteristics through measurements and simulation of line radiation and propagation characteristics. An artificially made sparking noise generator, which is mounted on a power line, is used as noise source and the radiation characteristics are measured. Measurements were carried out in different environments, which included a high-voltage laboratory (HV-Lab), a 40m test-line, and another 22-kV test line of approximately 1.5 km. The key sparking noise parameters of interest were the temporal and spectral characteristics. The time domain features considered were the pulse shape and the repetition rate. The lateral, longitudinal and height attenuation profiles were also quantified. Since sparking noise current pulses are injected or induced onto power line conductors, the line will act as an unintentional antenna. The far-field radiation characteristics of the line were evaluated through measurements on physical scale-model structures and simulations. 1/120th and 1/200th scaled lines, using an absorbing material and metallic ground planes, respectively, were simulated in FEKO. The measurements of the constructed scale models were taken in the anechoic chamber. Both measurements and simulations showed that the line exhibits an end-fire antenna pattern mode. Line length, pulse injection point and line configuration were some of the parameters found to affect the radiation patterns. The findings from this study are used to determine techniques to identify the sparking noise, and locate and correct the sources when they occur on the line hardware. Appropriate equipment is recommended to be used for the location and correction of sparking noise.AFRIKAANSE OPSOMMING: Die Vierkante Kilometer Reeks (SKA) en sy demonstrasie projek, die Karoo Reeks Teleskoop (KAT), word ontwerp om oor 'n wye frekwensie-bereik te funksioneer. Beide sal na verwagting beter sensitiwiteit en resolusie as bestaande radioteleskope he. Die radio-astronomie-gemeenskap is deeglik bewus van die negatiewe impak wat radio-frekwensie steurnisse (RFS) op waarnemings in die voorgestelde frekwensieband het. Die rede hiervoor is dat swak radio-seine soos die van pulsars en verafgelee sterrestelsels inherent moeilik is om te bepaal. Die teenwoordigheid van RFS bronne in die teleskoop se onmiddellike operasionele gebied kan waarnemings nadelig beinvloed. Dit lei uiteindelik tot onakkurate of misleidende resultate. Kraglyne en uitstralings van elektriese heinings is voorbeelde van RFS bronne. Metodes om die oorsake van die steurnisse van die SKA se elektromagnetiese omgewing te verminder is noodsaaklik om die sukses van hierdie projekt te verseker. Dit vereis egter deeglike begrip van die eienskappe van hierdie bronne. Steurnisse as gevolg van oorhoofse kraglyne word hoofsaaklik veroorsaak deur korona en gapingtipe ontladings (algemeen bekend as vonkontladings). Vonkontladings word hier beskou as die belangrikste oorsaak van steurnisse vir die SKA. Dit word in die Suid-Afrikaanse netwerk hoofsaaklik aangetref op houtpaal-installasies, wat gewoonlik bestaan uit distribusie lyne wat tot en met 66 kV wisselstroom (WS) bedryf word. By hierdie operasionele spanning is die spanningsgradient op die lyn onvoldoende om korona op te wek. Die kragvereistes vir die SKA se voorafgaande projekte sal sodanig wees dat hierdie spanningsvlak nie oorskry sal word nie. Die doel van die navorsing omskryf in hierdie proefskrif is om die eienskappe van vonkontladings rondom kraglyne te evalueer. Dit word gedoen met behulp van metings en simulasies van uitstralings- en voortplantingspatrone wat met 'n spesifieke lyn geassosieer kan word. 'n Kunsmatige vonkontladingsopwekker word op 'n kraglyn geplaas en dien as bron om die uitstralingspatrone te meet. Metings is uitgevoer in verskillende omgewings, insluitende 'n hoogspanningslaboratorium (HV-Lab), 'n 40 m toetslyn en 'n 22 kV WS toetslyn van ongeveer 1.5 km lank. Die hoof vonkontladings eienskappe van belang is die temporale en spektrale eienskappe. Die tydgebiedeienskappe wat ondersoek is, is die pulsvorm asook die pulsherhalingskoers. Die laterale, longitudinale en hoogte-attenuasie profiele word ook gekwantifiseer. Aangesien stroompulse deur vonkontladings op die kraglyn geplaas of geinduseer word, sal die lyn as 'n ongewenste antenna optree. Die ver-veld uitstralingskenmerke van die lyn is ook geëvalueer deur gebruik te maak van fisiese skaalmodelstrukture en -simulasies. 1/120ste en 1/200ste geskaleerde lynmodelle, wat onderskeidelik 'n absorberende- en metaalgrondvlak bevat, was gebruik om 'n 3 spanlengte kraglyn te simuleer met behulp van FEKO. Metings van die fisiese skaalmodel strukture is in 'n anegoise kamer geneem. Beide die metings en die simulasies toon dat die lyn 'n endpunt uitstralingspatroon het. Lynlengte, die opwekkingsposisie van die stroompuls en die lynkonfigurasie is 'n paar van die parameters wat die uitstralingpatroon beïnvloed, soos in die navorsing aangedui. Die bevindinge van hierdie studie word gebruik om steurnisse as gevolg van vonkontladings op die kraglyn te identifiseer, op te spoor en uiteindelik reg te stel. Toepaslike toerusting word voorgestel wat gebruik kan word vir die identifisering en opsporing van vonkontladings

Understanding water and land use within Tana and Athi River Basins in Kenya: opportunities for improvement

Koech, RK ORCiD: 0000-0002-0563-6687River basins are the modern-day regions for integrated planning and management of watersheds, groundwater, land use, river regulation, food security and healthcare development in most countries. The Tana and Athi River Basins, being home to over 40% of Kenya’s population, major hydroelectric dams and many irrigation schemes, are considered important areas of focus for sustainable agricultural production. However, competing water demands and water scarcity are posing a great challenge for decision-makers as well as farming communities. Despite these challenges, new agricultural and water projects are planned for implementation, raising doubts on the current and future state of the basins’ water resources. This investigation highlights the extent to which the ongoing and future agricultural water-related developments are supported by scientific research and helps invigorate and organise critical thinking on potential investments and policies in the basins. An update and information on the understanding of the basins’ land and water dynamics are provided. Analysis of the literature reviewed highlighted a limited scientific knowledge base at watershed scale, inadequate data as well as gaps in the available data and the need for application of current state-of-the-art technologies in whole basin water management. Some opportunities for improvement in data management and technology application are also suggested. This information contributes to expanding knowledge base on biophysical areas key to the basins’ meeting their integrated water management

Understanding water and land use within Tana and Athi River Basins in Kenya: opportunities for improvement

River basins are the modern-day regions for integrated planning and management of watersheds, groundwater, land use, river regulation, food security and healthcare development in most countries. The Tana and Athi River Basins, being home to over 40% of Kenya's population, major hydroelectric dams and many irrigation schemes, are considered important areas of focus for sustainable agricultural production. However, competing water demands and water scarcity are posing a great challenge for decision-makers as well as farming communities. Despite these challenges, new agricultural and water projects are planned for implementation, raising doubts on the current and future state of the basins' water resources. This investigation highlights the extent to which the ongoing and future agricultural water-related developments are supported by scientific research and helps invigorate and organise critical thinking on potential investments and policies in the basins. An update and information on the understanding of the basins' land and water dynamics are provided. Analysis of the literature reviewed highlighted a limited scientific knowledge base at watershed scale, inadequate data as well as gaps in the available data and the need for application of current state-of-the-art technologies in whole basin water management. Some opportunities for improvement in data management and technology application are also suggested. This information contributes to expanding knowledge base on biophysical areas key to the basins' meeting their integrated water management

Impacts of Climate Change and Land Use on Water Resources and River Dynamics Using Hydrologic Modelling, Remote Sensing and GIS: Towards Sustainable Development

The aerial photographs, taken on the 6th of February 1975 at a scale 1: 50 000, were obtained from the Survey of Kenya and were used to generate my original data

Impacts of Climate Change and Land Use on Water Resources and River Dynamics Using Hydrologic Modelling, Remote Sensing and GIS: Towards Sustainable Development

Water sustains life and ecosystems of the earth, making it an essential and important resource. However, it has become scarce, particularly in semi-arid regions of the globe, because of climate change, human population growth and growing economies. These factors can substantially impact on water resources, riverine ecosystems and services. Sustainable development of water resources and water system-related activities, such as agriculture, in river basins require an in-depth understanding of the present status and trends of hydrometeorological patterns, land use/land-cover and river channel dynamics in order to balance growth and integrity of vital environmental systems. Assessment of climate and land use impacts on water resources in the Tana River Basin (TRB), Kenya, as a typical example of Eastern Africa watersheds, was the main goal of this research. The focus was the Tana River Basin (TRB) in Kenya as a typical example of Eastern Africa watersheds. Land use/cover changes, hydroclimatic, hydro-geomorphology and morphometry of the basin including channel planform and floodplain corridor time series were characterised as well as historical modelling of climatic dynamics. The methods and tools applied were literature review, hydrological modelling, remote sensing (RS) and geospatial analysis techniques. Hydroclimatic data were obtained from Water Resources Management Authority (WRMA) of Kenya and remote sensing data were sourced from Survey of Kenya and Landsat Archive of United States Geological Survey (USGS). The first step of this investigation was a detailed literature review on the TRB and its adjacent Athi River Basin (ARB) to provide insights on the state of water resources. Limited scientific knowledgebase at watershed scale, inadequate data as well as gaps in the available data and the need for application of current state-of-the-art technologies were the major problems identified to affect whole basin water management and recommendations were made for better planning and management. The second step was to assess the spatio-temporal dynamics of land use/cover over a 28-year period in the upper TRB using digital change detection techniques. The results indicated substantial increase in agricultural land and builtup area and decrease in open land, waterbodies and vegetation. There was a large expansion of agricultural land to marginal semi-arid and arid areas (lower part of the basin) over the period. These changes have potential implications on water resources and environment. The third step was to investigate temporal variabilities and trends of rainfall and discharges in the TRB using statistical methods including Mann–Kendall non-parametric test and bootstrapping to capture and detect multiannual and seasonal variabilities and monotonic trends over a period of 75 years. The results suggested that the streamflow is largely dependent on increasing rainfall at the highlands which also seemed to be influenced by altitudinal factors. The precipitation exhibited spatio-temporal variabilities and trends. The streamflow also showed statistically significant upward monotonic trend and seasonal variability. The trends and time series data confirmed the potential evidence of climate and land use change and their impacts investigated in the previous step. The fourth step was to study recent hydromorphological characteristics and ecohydrological parameters using flow duration curve, freely available satellite data and geospatial analysis techniques. This study underscored the contribution of human and climate factors to streamflow changes and river channel morphology. The fifth step was to use Digital Elevation Model (DEM) to analyse morphometric parameters of the basin. This morphometric analysis of the basin provided the description of topography, geology and basin hydrological behaviour valuable for assessment and management of the basin water resources. The sixth step was to review methods for assessing probability distribution and associated parameter estimation procedures in the flood frequency analysis and apply the most efficient and robust approach in selecting the best models for fitting hydrological streamflow extremes in the basin. An assemblage of the latest computer statistical packages (fitdistrplus and HydroTSM) in an integrated development environment for the R programming language was applied. Maximum Likelihood Estimation (MLE), Goodness-of- Fit (GoF) tests-based analysis and information criteria-based selection procedures were used to identify the most suitable distribution models for forecasting hydrologic events and detecting inherent stochastic characteristics of hydrologic variables. This step provided a significant contribution on the current updates and understanding of predicting extreme hydrological events for various purposes, not only in the TRB but also in the methods that may be used in other regions. In the seventh step, river channel dynamics, in particular channel erosion and accretion, which are natural autogenic occurrences for fluvial rivers but accelerated by human modifications and climatic factors, were examined in detail. Remote sensing and geographic information system tools and techniques, aerial photographs, and satellite imagery were used to determine epochal channel erosion, accretion, and unchanged locations along the river. A geospatial methodological framework for monitoring river erosion and accretion was developed and applied to model and monitor, quantify and visualise the channel dynamics at reach scale. In the seventh step, another integrated remote sensing and GIS methodological framework was developed and used to study a total of 44 km reach of the channel morphological pattern changes (planform) and flood corridor dynamics of the river systems. In these studies, tremendous alteration in active channel and floodplain morpho-dynamics indicated substantial spatio-temporal dynamics and an overall vulnerability of the river condition. Lastly, scientific literature on modelling climate impacts on hydrology and water resources in river basins of the world was systematically reviewed and synthesized. The emphasis was on hydrologic modelling in terms of geography, global circulation models’ (GCMs), and downscaling, hydrologic models research topics and methods. Issues of uncertainties identified and discussed under this topic related to hydrologic model parameter estimation and hydrologic models themselves, GCM downscaling to application scale, stationarity in hydroclimatic variables, use of remote sensing products and geospatial analysis tools, and modelling of water quality. This research contributes information and knowledge that are of practical application to planning and management of water systems and policy decision-making in the water-foodenergy nexus within and without the basin. It provides guiding principles among other factors, for governments in this region in planning long-term viability and sustainability of riverine infrastructure and other regional projects such as those prioritised in the Comprehensive Africa Agriculture Development Programme (CAADP). The research also provides a basis for further modelling of river resources and environment under climate and human behaviour dynamics

Monitoring river channel dynamics using remote sensing and GIS techniques

River channel dynamics are natural autogenic occurrences for fluvial rivers with influences from human modifications and climatic factors. Remote sensing and geographic information system tools and techniques, aerial photographs, and satellite imagery have been used to determine epochal channel erosion, accretion, and unchanged locations along Tana River, Kenya's longest river. Six reaches within a 142-km Saka-Mnazini stretch were studied by comparing sequential changes in the position of the channel in 1975–1986, 1986–2000, 2000–2017, and 1975–2017 epochs. Manual and automatic digital processing procedures and GIS tools were applied to visualize and quantify the reach-wise spatial and temporal morphological changes. The erosion and accretion channel changes over the study period were observed and quantified at all reaches. Meandering and switching off or abandoning the main active channel was also illustrated. The potential driving forces of morphological changes included varying hydrological regime, upstream land use practices, nature of channel gradient, and riparian vegetation occurrence changes. We found no clear evidence to link river regulation with the river channel dynamics. Results deliver the latest evidence on the dynamics of Tana River. This information is crucial for understanding river evolution characteristics and aid in planning and management at the lower reaches which has remained poorly understood. Use of remote sensing data in concert with GIS provides efficient and economical quantitative spatial and temporal analysis of river channel changes

Identification of the Most Suitable Probability Distribution Models for Maximum, Minimum, and Mean Streamflow

Hydrological studies are useful in designing, planning, and managing water resources, infrastructure, and ecosystems. Probability distribution models are applied in extreme flood analysis, drought investigations, reservoir volumes studies, and time-series modelling, among other various hydrological studies. However, the selection of the most suitable probability distribution and associated parameter estimation procedure, as a fundamental step in flood frequency analysis, has remained the most difficult task for many researchers and water practitioners. This paper explains the current approaches that are used to identify the probability distribution functions that are best suited for the estimation of maximum, minimum, and mean streamflows. Then, it compares the performance of six probability distributions, and illustrates four fitting tests, evaluation procedures, and selection procedures through using a river basin as a case study. An assemblage of the latest computer statistical packages in an integrated development environment for the R programming language was applied. Maximum likelihood estimation (MLE), goodness-of-fit (GoF) tests-based analysis, and information criteria-based selection procedures were used to identify the most suitable distribution models. The results showed that the gamma (Pearson type 3) and lognormal distribution models were the best-fit functions for maximum streamflows, since they had the lowest Akaike Information Criterion values of 1083 and 1081, and Bayesian Information Criterion (BIC) values corresponding to 1087 and 1086, respectively. The Weibull, GEV, and Gumbel functions were the best-fit functions for the annual minimum flows of the Tana River, while the lognormal and GEV distribution functions the best-fit functions for the annual mean flows of the Tana River. The choices of the selected distribution functions may be used for forecasting hydrologic events and detecting the inherent stochastic characteristics of the hydrologic variables for predictions in the Tana River Basin. This paper also provides a significant contribution to the current understanding of predicting extreme hydrological events for various purposes. It indicates a direction for hydro-meteorological scientists within the current debate surrounding whether to use historical data and trend estimation techniques for predicting future events with issues of non-stationarity and underlying stochastic processes

Geospatial modelling of the inundation levels in the Sundarbans mangrove forests due to the impact of sea level rise and identification of affected species and regions

This research reveals the magnitude of mangrove area loss and future impacts on mangrove species composition and distribution due to rise in Mean Sea Level (MSL). In this study, a geospatial model of potentially inundated areas was developed using Digital Elevation Model (DEM) data to assess the potential impacts of sea level rise (SLR) on the spatial distribution of mangrove species and estimate the potential inundation and subsequent mangrove area loss. The mangrove areas of 2646 ha, 9599 ha and 74,720 ha are projected to be inundated and subsequently lost by the end of the twenty first century for the low, medium and high SLR scenarios respectively under the net subsidence rate −2.4 mm/year relative to the baseline year 2000. All the major five mangrove species of the Bangladesh Sundarbans will be affected and this can potentially contribute to a change in the present species composition and biodiversity of the forest. Results suggest that, under the extreme scenario, inundation and subsequent loss of different mangrove species will be substantial and this can bring a massive change in the species composition and their spatial distribution in the Bangladesh Sundarbans