1,721,058 research outputs found
A comparative study of Phoebetria albatrosses' interactions with mesoscale oceanographic features south of the African continent
No full textTwo sympatric Phoebetria albatrosses, P. fusca and palpebrata breeding at Marion Island in the South Indian Ocean were studied. Adult individuals were tracked between 2008 and 2011. The study examined the foraging distribution of the two species in relation to environmental parameters such as sea surface temperature. Interaction with mesoscale features expressed by sea surface temperatures, was tested with statistical models. Tracked P. fusca demonstrated positive association with sea surface temperatures in the Southern Indian Ocean, in particular during incubating and chick-provisioning periods, by travelling shorter distances to the interfaces of mesocale features created as a result of the Agulhas Return Current located << 500 km to the north of breeding islands. During nest construction, tracked P. fusca travelled greater distances in search of food possibly because they had no chick to return to at the colonies. Contrastingly, tracked P. palpebrata did not demonstrate any positive association with sea surface temperatures. During incubating and chick-provisioning periods, tracked P. palpebrata travelled shorter distances to foraging grounds located to the south of breeding islands possibly to maximise returns to chicks while minimising efforts. During nest construction, tracked P. palpebrata travelled to distant foraging grounds to the south of the Antarctic Polar Front in areas of low mesoscale variability suggesting that greater distances can be achieved when they have no chick to feed at the colonies. Individuals of both tracked species foraged within close proximity during energy-demanding periods indicating their ability to employ an efficient foraging strategy that ensures minimal effort whilst maximising returns. Generalised Linear Models with the response variable being species and explanatory variables comprised of sea surface temperatures, annual breeding stages, distance traversed and activity, were conducted to examine the effect of environmental factors on seabird foraging distribution. These models were subjected to robust fitness tests and those that represented ecological reality of the two tracked albatrosses were chosen. The study demonstrates that the most important foraging areas for these two tracked seabird species overlap with the Indian Ocean Tuna Commission Convention area making them vulnerable from incidental capture from high longline fisheries. These results have implications to the conservation of these albatrosses suggesting a need for a multi-faceted approach on fisheries management particularly on mitigation of seabird bycatch in the Indian Ocean Tuna Convention area
Impacts of ENSO on coastal South African sea surface temperatures
Full text linkThe impact of El Niño Southern Oscillation (ENSO) on the Southern African inland climate is well documented and provides skill in the seasonal forecast of rainfall but little is known of the impact of ENSO on the ocean surrounding South Africa. The aim of this study is to assess the impact of ENSO on sea surface temperatures around the coast of South Africa and to calculate SST trends around the coast. I start by updating the study of Rouault et al (2010) on the very topic with an additional 10 years of data and two additional newer datasets which allow sampling closer to the coast where wind-driven upwelling is more active. The new highresolution ERA 5 reanalyzed climate dataset is also used to look at the atmospheric forcing of sea surface temperatures by ENSO. As in Rouault et al. (2010), I study five similar threedegree-long coastal regions around South Africa, namely: West Coast, South Coast, Port Elizabeth/Port Alfred, Transkei, Kwazulu-Natal and a larger offshore Agulhas Current area domain. Three SST datasets are evaluated in this study: the 1 ̊x1 ̊Optimal Interpolation sea surface temperature (OI SST) used by Rouault et al (2010), the 0.25 ̊x 0.25 ̊ Optimal Interpolation SST and the 4 km x 4 km Advanced Very High-Resolution Radiometer (AVHRR) Pathfinder SST version 5.3. The 0.25 ̊x 0.25 ̊OI SST resolvesSST anomalies better in these coastal regions as compared to 1 ̊x1 ̊ OISST. The difference in results among the three products concerning trends and correlation with ENSO is a cause for concern. The 4 km x 4 km AVHRR Pathfinder allows for SST to be extracted even closer to the coast but missing values are numerous and hamper the use of this dataset for ENSO composites and trend analyses. Results show a significant positive correlation with El Niño in summer at the monthly scale, reaching a maximum correlation of 0.45 at 3 months lag. Correlation is the highest in late summer. There is a negative correlation in the Agulhas Current area, opposite to those with ENSO and West Coast. The impact of ENSO on the coast of South Africa, West Coast and South Coast is due to change in surface wind speed with weaker upwelling favorable during El Niño leading to warmer than normal coastal water SST and stronger than normal Southeasterly winds during la Niña leading to cooler than normal coastal water. The wind perturbation is part of largescale basin-wide perturbations in the tropical Atlantic, in the South Atlantic high-pressure atmospheric system and in the westerly wind pattern of the midlatitude to the south. Non-ENSO related impact can be as important as ENSO related SST perturbation and is also linked to large scale perturbations in the South Atlantic. There is no relation between the strength of ENSO and the strength of the perturbation, and some ENSO events do not lead to the expected canonical warming or cooling. The large-scale SST perturbations seem to be caused by anomalous surface turbulent flux of latent and sensible heat and abnormal wind speed and direction. This study opens the possibility of seasonal forecasting of SST in the South Benguela upwelling system because of the positive lag correlation between ENSO and SST with ENSO leading SST
The influence of the Agulhas Current on two South African extreme weather events
No full textIncludes bibliographical references.Surface station, satellite and NCEP re-analysis data are used to examine the evolution of two severe storms that occurred over the eastern coastal regions during South Africa's summer season 1998/99. The storms in November and December were both accompanied by heavy rainfall in two widely separated locations. The storm in December proved to be more severe as it resulted in flooding while tornadoes were reported in the Umtata and Hogsback regions of the Eastern Cape. Both storms appeared to result from interaction between a continental heat low, advection of warm moist air around an anticyclone in the South-west Indian Ocean and an approaching midlevel westerly trough. NCEP derived moisture flux diagrams and back trajectories of air parcels constructed from ECMWF data suggest that the Agulhas Current region was a major source of low level moisture for both storms. TRMM satellite imagery captured heavy rainfall above the high sea surface temperatures of the Agulhas Current. TRMM measurements of rainfall and latent heat in the atmosphere show that the high sea surface temperatures of the Agulhas Current modified the mesoscale environment above the current. To what extent the mesoscale environment above the Agulhas Current modified the synoptic situations over land could be answered using regional modeling and more frequent radiosonde data
The process of conserving biodiversity: From planning to evaluating conservation actions on private land in the Cape Lowlands, South Africa
No full textConservation can be conceptualised as a process of linked phases that contribute to bringing about effective biodiversity protection: (i) a conservation assessment that identifies spatially explicit conservation priorities to provide strategic guidance on where best to invest conservation resources; (ii) a planning phase that takes the spatial priorities forward into implementation processes by setting out a strategy and schedule for undertaking conservation action; (iii) an implementation phase during which conservation interventions are executed; and (iv) an evaluation phase to investigate whether conservation has been successful. In practice, conservation is rarely conducted in this way. The interrelated phases are often undertaken separately, links are neglected, and conservation science to date has focused primarily on the conservation assessment. This has led to the development of highly sophisticated principles and techniques for locating priority conservation areas, but planning and evaluation have received limited research attention: few published studies demonstrate collaborative planning processes that assist with putting conservation assessments into practice, or show on-theground conservation success linked to effective conservation planning and implementation processes. My PhD research aimed to address these knowledge gaps by conducting a conservation assessment and collaborative planning phase that would lead to effective conservation action as determined by an evaluation. The study area was in the critically endangered Cape Lowlands, a conservation priority area in the Cape Floristic Region, South Africa. The highly transformed agricultural production landscape is mostly privately owned; formal biodiversity protection is low; and remnants of natural vegetation (< 9% is left) harbour an exceptionally diverse flora. Strategic conservation interventions coordinated across the Cape Floristic Region (CFR) provided the overall implementation context in the Cape Lowlands. My research was conducted in this real-world practical situation and addresses the whole conservation process, from assessment to evaluation of conservation actions. I first developed a conservation assessment guided by three key questions: âWhat are feasible, efficient, defensible and efficacious solutions for (i) deriving a surrogate layer that represents biodiversity in a region which is characterised by exceptional plant species richness and endemism ; and (ii) considering the connectivity of natural areas in an ecosystem that is highly transformed, fragmented and largely unprotected?â; and âHow can a selection method be developed for identifying and prioritising key biodiversity areas in a landscape identified as 100% irreplaceable?â To answer these questions I identified feasible, efficient, defensible methods focusing on three key aspects: (i) producing a biodiversity surrogate map of original vegetation cover using two alternative approaches: simple expert mapping and statistical modelling integrating plant species and environmental data; (ii) designing selection units based on vegetation connectivity in a simple technique to include spatial attributes of conservation areas before identifying key biodiversity areas; (iii) developing a prioritisation method based on a simple scoring system and verifying results with MARXAN-selected priority areas. In all vi three cases I found that the simple conservation assessment methods produced suitable outputs for further integration in the assessment and in decision-making during planning. (i) The expert map was as effective as the vegetation model and required fewer resources to be produced since the model relied on resource-intensive species data collection. (ii) In comparison with commonly used cadastre-based units, connectivity-based selection units captured connected vegetation more effectively and area-efficiently in units that served as the basis for priority area selection. (iii) Scoring provided a feasible, defensible mechanism for prioritising key biodiversity areas in the Cape Lowlands where all remaining vegetation has been identified as 100% irreplaceable. The planning phase complemented the assessment. Key guiding questions here were âHow can collaborative planning be used to translate the conservation assessmentâs technical outputs into timebased conservation goals and into useful products for implementation?â and âWhat constitutes effective planning in the conservation process? Through a collaborative scheduling process, I developed timebased conservation goals for action in the Cape Lowlands. This was undertaken in two work sessions with scientists, planners and conservation practitioners from the implementing agency, CapeNature. Scheduling was guided by (i) scoring-derived biodiversity-driven spatial priorities that made intuitive sense to implementers; and (ii) conservation opportunities and constraints (including resources) identified by the practitioners. Scheduling was conducted with reference to the on-going development of a private land conservation strategy for the CFR to be piloted in the Cape Lowlands. The scheduling process was an effective platform for taking spatial priorities from the assessment towards implementation: the discourse-based collaborative planning was constructive and led to consensusbased final products, including a 20-year and 5-year conservation plan setting out spatially explicit goals for conservation interventions in the Cape Lowlands. The main limitation of the process was that resource planning was not integrated explicitly enough to identify realistic goals. This highlighted the importance of integrating detailed resource considerations in future planning. Finally, to address the question âTo what extent has the Cape Lowlands conservation plan been implemented after five years of off-reserve conservation interventions in the region?â I developed a protocol for evaluating the effectiveness of conservation action in the Cape Lowlands. I assessed (i) the extent to which the goals conservation plans produced in the planning phase had been implemented; and (ii) the achievements of incentive-based conservation stewardship interventions on private land in the Cape Lowlands and CFR. Achievements were measured as hectares of vegetation protected through voluntary and legally-binding contractual conservation agreements between landowners and conservation organisations. The evaluation revealed that (i) CapeNatureâs stewardship interventions in the Cape Lowlands focused on priority areas identified in the 5- and 20-year conservation plans, thus demonstrating effective execution of the plans; (ii) private land conservation interventions have been remarkably successful and cost-effective: 68604ha priority vegetation were protected in the CFR under conservation agreements by end 2007, rivalling private land biodiversity conservation in the U.S.A. and Latin America, and more than 8000ha in the critically endangered Cape Lowlands at a cost of R 6.8 vii Million (< 1 million US$). The evaluation identified the long-term financial sustainability of current implementation programmes as the most significant threat to future success in private land conservation interventions in the Cape Lowlands and CFR. There is significant scope to design future monitoring and evaluation systems to measure ecological gains due to specific conservation actions, not done in the Cape Lowlands study, and to tailor approaches to suit specific programme stages. This PhD provides a rare overview of an entire conservation cycle with linked phases that has led to biodiversity protection. The study highlights that an effective long-term process demands significant investment in (i) a diverse (growing) set of skills and expertise to solve complex conservation situations; (ii) time, especially for visible implementation success; and (iii) well-allocated resources (money, time, skills, research attention) across all phases in the conservation process. This is necessary as each phase is needed to achieve the ultimate conservation goal: I show in the Cape Lowlands that a simple conservation assessment with limited funds (R1.8 million over 3 years) can be highly effective in guiding action towards priority areas. Important here is to develop rapid, defensible methods for cost-effective assessments and linking these with in-depth planning processes. Planning and evaluation in the Cape Lowlands were essential connecting phases that continue to support implementation success. In the context of on-going conservation action, planning and evaluation need to become part of a cyclical conservation process geared towards improved practices. I suggest that significantly greater investment in planning and evaluation research is essential to move conservation science forward in fulfilling its fundamental goal of strategically guiding where, when and how to invest optimally in conservation interventions. This will be exceptionally beneficial for undertaking effective conservation interventions and will help to clearly demonstrate the value of the research for conservation practice
Sea surface temperature trends around Southern Africa (focusing on the Benguela Current system and the Agulhas retroflection area)
No full textIncludes bibliographical references.Sea surface temperature (SST) fluctuations and changes around southern Africa have important consequences on regional weather, climate and the marine ecosystem. SST is a good indicator for upwelling strength in the Benguela Current system and therefore is linked to bio logical activity in that region. SS T is an important driver of the air-sea exchange of moisture and energy, especially in the Agulhas Current where high latent and sensible heat fluxes occur. It is important to quantify SST trends with accuracy for the long term monitoring and characterisation of weather, climate and marine ecosystem in southern Africa, especially in the context of climate change. Here various 1° x 1° SST datasets are used to calculate yearly time series, inter-annual fluctuations and trends in key oceanic regions of southern Africa. OI SST, Hadley SST, NOCS SST and ER SST (which has 2° x 2° resolution) are used in this study. I start calculating trends and inter- annual fluctuations for various domains and dataset in the recent satellite era since 1982 to compare the non-satellite products NOCS SST and ER SST with the satellite products Hadley SST and OI SST. The idea is to validate the no n-satellite products since 1982 and then use them to calculate trends around southern Africa before 1982. Trends and inter-annual fluctuation in the Angola Benguela Current system and the Agulhas Current retroflection system are therefore presented for all datasets for the 1982 - 2012 period. The datasets show different trends and different timing or amplitude of inter- annual variability. This prevents the estimation of changes in the region with confidence before the satellite era which was the initial objective of the study. The main reason is that ER SST is a 2° x 2° dataset and maybe not adequate for upwelling region and the Hadley SST 1° x 1° dataset include satellite data from 1980 which creates some non-homogeneity in time and probably an artificial cooling at the coast from the 1980’s when satellite data is introduced in the dataset to patch the observational gaps. It is therefore not advisable to use Hadley SST for trend studies including 1982 onwards. From 1982 to 2012 in the Benguela upwelling system, whereas OI SST and Hadley SST show mainly cooling trends of different magnitude, NOCS SST and ER SST show warming trends with NOCS showing significant (p < 0.05) warming trends which is suspicious. In the Northern Benguela and Retroflection all datasets show warming trends for the 1982 - 2012 period except from NOCS SST
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A two-year long drought in summer 2014/2015 and 2015/2016 over South Africa
Full text linkDroughts occurred over South Africa during the summer seasons of 2014/2015 and 2015/2016. At the same time, the Pacific Ocean was warmer than normal starting in 2014 and leading to the very strong 2015/2016 El Niño. The first objective of this study is to document the ocean and climate conditions that occurred during the summer seasons 2014/2015 and 2015/2016 in southern Africa. NCEP Reanalysis data is used to compute the monthly and seasonal scale composite mean and anomalies of large-scale circulations during the summer seasons of 2014/2015 and 2015/2016. Results obtained from the study suggest that some months of 2014/2015 and 2015/2016 were canonical to the effect of El Niño over southern Africa, but not all of them during the summer seasons were dry. The wetter than normal conditions in northeast South Africa, Botswana and Zimbabwe during December 2014 are unfamiliar for a canonical summer El Niño event over southern Africa. Anomalous cooler than normal Sea Surface Temperature (SST) occurred over the west coast and south coast during December 2014 and February 2015, while it is usually warmer during El Niño. Additionally, the colder than normal SST at the south coast during February 2016 and Namibian and West Coast during March 2016 does not mimic the canonical El Niño patterns. However, this did not influence the El Niño-like warmer seasonal SST average during 2015/2016. The lower than normal pressure anomalies over the subcontinent during December 2014 and January 2015 were not portraying a canonical El Niño pattern but the other months were. The seasonal larger than normal pressure at 500 hPa over the subcontinent was more typical of El Niño during summer 2015/2016 and acted to suppress rainfall. Secondly, the study uses the Standard Precipitation Index (SPI) at different time scales (3 months duration, 5 months duration and 17 months duration) to assess the severity of 2015/2016 summer drought compared to the other droughts of the 20th and 21st century (1921 to 2016) and to analyse the relationship between droughts and ENSO. The South African Weather Service (SAWS) rainfall data shows that KwaZulu-Natal was the only region within South Africa, to have the 2015/2016 as the strongest summer drought since 1921 but 2015/2016 was still one of the worst droughts on record in South Africa, especially at the 2 consecutive seasonal scales. In general, droughts are favored by El Niño and wetter conditions by La Niña, but the second strongest El Niño of 1997/1998 led to near normal rainfall over the north-eastern region at all time-scales. The SPI has proven to be very versatile, flexible and very effective to monitor the 2015/2016 summer drought in the complex South African rainfall regime. However, there was little difference between 3 months SPI at the end of February and 5 months SPI at the end of March. For South Africa, the summer rainfall 2015/2016 season had the fifth worst drought after El Niño related drought of 1982/1983 and 1991/1992 and the non-El Niño related droughts of 1967/1968 and 1944/1945. At the 17-month scale, an index that encompasses two summer seasons 2015/2016 was the third worst drought since summer 1921/1922 due to dry conditions in 2014/2015 and 2015/2016
Impact of the Agulhas Current on storm development
Full text linkA high-resolution atmospheric model (WRF) is used to investigate the impact of the Agulhas Current on synoptic storm development. A sensitivity experiment is conducted to analyse the influence of the Agulhas Current's sea surface temperature (SST) on rain producing, synoptic scale weather features. Two model configurations: Control (CTL) and Smooth (SMTH) are analysed to understand the effect of the Agulhas Current's SST and high latent heat fluxes on storms that develop or track over the Current. The two configurations are identical except that the SMTH simulation has the SST signature of the Agulhas reduced by smoothing out the strong SST gradients associated with the Current. This results in the Agulhas Current core having SSTs reduced by roughly 1.5°C in the SMTH configuration. Consequently, lower (100 - 150 W.m¯²) latent heat fluxes are also simulated at the Current core's location in the SMTH run. Using daily South Africa Weather Service synoptic charts from 2001 - 2005, when the model output is available, two hundred (200) synoptic scale storms are found to track over the Current. Using the TRMM 3B42 3-hourly 0.25 x 0.25° precipitation rain rate product, 70 (of the 200) are found to have produced rainfall. Five model variables are used as proxies for the storm intensity of these 70 storms. Ten storms are found to show storm intensification when passing over the Current. In the CTL simulation, of these ten storms, ten show lower 850mb geopotential heights (m), nine show higher surface wind speeds (m.sˉ¹), seven show higher rain rates (mm.hrˉ¹), eight show higher Eddy Kinetic Energy (EKE) (m².sˉ²) and nine show greater upward moisture flux at the surface (g.mˉ².sˉ¹) compared to the SMTH run once each storm has propagated over the Current. Model output analysis shows sustained or dissipating storm intensity of the other 60 storms while passing over the Current. Nonetheless, these results provide a strong case for the influence of the Agulhas Current on the intensification of synoptic scale, rain producing events
Water vapour transport from the South Atlantic and Indian Oceans and summer rainfall in southern Africa
No full textIncludes bibliographical references (p. 190-206).Moisture input from the South Atlantic and Indian Oceans over southern Africa is examined through zonal water vapour transport. Along the west coast, variations in intensity and latitudinal position of the South Atlantic anticyclone/modulations of the westerly flow that penetrates from the tropical Atlantic, contribute the most about 25% and 11% of the variance explained respectively), in January-February to variability in moisture advection from the South/tropical Atlantic, thus affecting rainfall at subtropical/tropical latitudes respectively. The southern extension of the AEJ could play a role in transfering moisture from the tropics southwards during wet phases, while events related to low phases of the Southern Oscillation are marked by an eastward shift of the ascending branch of the Walker circulation, suppressing convection and thus reducing rainfall over the subcontinent
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