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Nitrogen oxides, particularly NO2, are emitted through a variety of industrial and transport processes globally. The world’s continuous economic development, including in developing countries, results in an increasing concentration of those gases in the atmosphere. Yet, there is scant information on the current state and recent evolution of these atmospheric pollutants over a range of spatial and temporal scales, especially in Africa. This, in turn, hinders the assessment of the emissions and the evaluation of potential risks or impacts on societies and their economies, as well as on the environment. This study attempts to fill the gap by leveraging data from a Pandora-2S ground-based, column-integrating instrument located in Wakkerstroom in the Mpumalanga Province of South Africa and space-based remote sensing data obtained from the TROPOMI instrument onboard the ESA Sentinel-5P satellite. We compare these two spatially (horizontal) representative data sets using statistical tools to investigate the concentrations of emitted and transported NO2 at this particular location, expecting that a significant positive correlation between the NO2 tropospheric vertical column (TVC) data might justify using the TROPOMI data, available globally, as a proxy for tropospheric and boundary layer NO2 concentrations over the Highveld of South Africa more generally. The data from the two instruments showed no significant difference between the interannual mean TVC-NO2 in 2020 and 2021. The seasonal patterns for both instruments were different in 2020, but in 2021, both measured peak TVC-NO2 concentrations in late winter (week 34). The instruments both detected higher TVC-NO2 concentrations during transitions between seasons, particularly from winter to spring. The TVC-NO2 concentrations measured in Wakkerstroom Mpumalanga are mostly contributed to by the emission sources in the low troposphere, such as biomass burning and emissions from local power stations.

ABSTRACT Sustainability-focused research networks and communities of practice have emerged as a key response and strategy to build capacity and knowledge to support transformation towards more sustainable, just and equitable futures. This paper synthesises insights from the development of a community of practice on social-ecological systems (SES) research in southern Africa over the past decade, linked to the international Programme on Ecosystem Change and Society (PECS). This community consists of a network of researchers who carry out place-based SES research in the southern African region. They interact through various cross-cutting working groups and also host a variety of public colloquia and student and practitioner training events. Known as the Southern African Program on Ecosystem Change and Society (SAPECS), its core objectives are to: (1) derive new approaches and empirical insights on SES dynamics in the southern African context; (2) have a tangible impact by mainstreaming knowledge into policy and practice; and (3) grow the community of practice engaged in SES research and governance, including researchers, students and practitioners. This paper reflects on experiences in building the SAPECS community, with the aim of supporting the development of similar networks elsewhere in the world, particularly in the Global South.

Social-ecological systems (SES) research has emerged as an important area of sustainability science, informing and supporting pressing issues of transformation towards more sustainable, just and equitable futures. To date, much SES research has been done in or from the Global North, where the challenges and contexts for supporting sustainability transformations are substantially different from the Global South. This paper synthesises emerging insights on SES dynamics that can inform actions and advance research to support sustainability transformations specifically in the southern African context. The paper draws on work linked to members of the Southern African Program on Ecosystem Change and Society (SAPECS), a leading SES research network in the region, synthesizing key insights with respect to the five core themes of SAPECS: (i) transdisciplinary and engaged research, (ii) ecosystem services and human well-being, (iii) governance institutions and management practices, (iv) spatial relationships and cross-scale connections, and (v) regime shifts, traps and transformations. For each theme, we focus on insights that are particularly novel, interesting or important in the southern African context, and reflect on key research gaps and emerging frontiers for SES research in the region going forward. Such place-based insights are important for understanding the variation in SES dynamics around the world, and are crucial for informing a context-sensitive global agenda to foster sustainability transformations at local to global scales.

Climate change is acknowledged as one of the greatest environmental and development challenges society faces. Many organisations are now encouraged to conduct assessments of the climate risks they will be exposed to over the next decades. The Global Change Institute (University of Witwatersrand, South Africa) conducted such an assessment for the southern Africa region, to identify some of the main clusters of climate-change related risks. A list of over fifty risks was scored and ranked using a modified-Delphi process; an iterative process of expert-driven risk identification and ranking that was informed from our collective experience and the literature. We focused on the likelihood and consequence in the mid-term (2041–2060) and scored each risk according to this time frame (risk score = [likelihood of event occurring] × [the impact of the event], moderated by the multiple lines of evidence available (Evidence confidence), and the expert rankings of the assessors (Scorer confidence)), using the assumption of the IPCC RCP8.5 climate scenario. The top quartile was organized into five clusters of risk: food insecurity; water shortages; failed energy transition; human heat stress; and risks to nature and the bioeconomy. This paper describes these risk clusters, explored through the lens of available literature, and analysed within the broader framework of the sustainable development goals (SDGs), and the individual and collective actions that can be taken to reduce or adapt to these risks. There are many technical solutions to these risks, but these typically are costly and only function up to a point where the risks become unmanageable. For solutions to be successful, a ‘systems view’ and the complex interlinkages between climate change and socio-economic development must be addressed. The interconnected and cross-sectoral nature of the climate risk domains certainly presents a challenge for governance; the success of some of the measures discussed in this paper depends on the existence of strong, well-resourced, well-coordinated and influential governance mechanisms and state institutions and focusing on investigating the many synergies that exist among solutions.

The Pongola Bush Nature Reserve lies in a narrow band along the escarpment between Mpumalanga and KwaZulu-Natal (KZN). Although referred to as ‘bush’, this vegetation type may be considered to fit into the intersection of two types of scarp forest: the Northern Afrotemperate Forest and the Southern Mistbelt Forest. The area was heavily logged in the early 1900s with the need for timber for the emerging gold mining industry in Barberton. The forest fragment is now protected but lacks formal tree diversity assessments, and this study sets out to establish its community composition and richness using a range of standard techniques. Distributed throughout the forest, 127 circular plots (each 80 m2) were surveyed. In these, 1152 stems were measured for species, height, and diameter at breast height (DBH). Four species contributed roughly 70% of the 70 Mg ha−1 above ground woody biomass. Stem size class distributions showed a high recruitment rate of small stemmed individuals and few large individuals. This pattern is consistent with the disturbance history of the site, with limited recruitment of certain species, mainly limited to early successional species. The Pongola Bush forest is particularly diverse in terms of tree species: 41 species were recorded, and it is estimated from the species area curve that there may be 70 tree species present. Conservation implications: This survey is the first formal tree diversity survey conducted on the Pongola Bush which may assist future research and conservation strategies.

Anthropogenic emissions from industry, biomass burning and traffic are significant contributors to the atmospheric loading of nitrogen dioxide on the South African Highveld. These sources are dispersed across the region and emit nitrogen oxides (NO and NO2) into the atmosphere at different elevations above the earth's surface. Additionally, atmospheric stability in the form of surface and elevated inversions decreases the dispersion of air pollutants and stratifies pollutants into distinctive layers above the surface. This study explores the Highveld near-surface nitrogen dioxide concentrations obtained using the ground-based Pandora-2s monitoring system. The Pandora-2s instrument retrieves surface NO2 levels from clear sky measurements using a fully parameterised algorithm. We present the first near-surface concentration measurements of atmospheric NO2 at Wakkerstroom, a site between Volksrust and Amersfoort, downstream of major source conglomerates, the Majuba power station and other industries. These data are explored in the presence and context of potential background NO2 concentrations in the area derived from other ground-based sensors. The quasicontinuous data show elevated surface NO2 levels in week 37 (September) of 2020 (7.3 ± 5.7 ppb), while the lowest levels were observed in week 15 (April) of 2020 (0.2 ± 0.04 ppb). The elevated surface NO2 levels are driven by dominant emission sources and transport trajectories, while the accuracy in the measurements is based on the high temporal resolution of the ground-based Pandora2s instrument.

The African woodlands known as miombo are one of the world’s largest currently relatively unexploited, but potentially arable, land resources. Miombo landscapes one of the top contemporary locations of conversion of dry forests to crop agriculture. This study investigates the net effect on climate forcing that results from different types of land use change in miombo, taking into account the multiple mechanisms through which the land interacts with the climate system, locally and globally. It finds that when miombo is converted tointensively cultivated commercial crops, the landscape-averaged 30-year net greenhouse gas forcing relative to intact woodlands is 309gCO2e m-2 y-1, of which net emission of carbon dioxide amount to 66%, non-CO2 greenhouse gas effects to 33%, plus unquantified contributions from ozone precursors and aerosols. We find that net brightening of the land surface resulting from clearing the woodlands generates a cooling effect larger than the greenhouse gas forcing (-1139gCO2e m-2 y-1). Greenhouse gas forcings resulting from transformation to extensive subsistence agriculture that are 78% lower than those from the intensive commercial agriculture path, and 40% lower if a transformation which sets out to mimic ecological processes in the miombo landscape is undertaken. Once the effect of surface brightening is included, then the total forcing for extensive subsistence agriculture is -834gCO2e m-2 y-1 , about the same as intensive commercial, and eco-agriculture is -102gCO2e m-2 y-1 . Taking into account the account the larger areas required for to achieve the same production, intensive commercial agriculture is the more climate-protective option.Keywords: greenhouse gas, net radiation, deforestation.

An optimal network design was carried out to prioritise the installation or refurbishment of greenhouse gas (GHG) monitoring stations around Africa. The network was optimised to reduce the uncertainty in emissions across three of the most important GHGs: CO2, CH4, and N2O. Optimal networks were derived using incremental optimisation of the percentage uncertainty reduction achieved by a Gaussian Bayesian atmospheric inversion. The solution for CO2 was driven by seasonality in net primary productivity. The solution for N2O was driven by activity in a small number of soil flux hotspots. The optimal solution for CH4 was consistent over different seasons. All solutions for CO2 and N2O placed sites in central Africa at places such as Kisangani, Kinshasa and Bunia (Democratic Republic of Congo), Dundo and Lubango (Angola), Zoétélé (Cameroon), Am Timan (Chad), and En Nahud (Sudan). Many of these sites appeared in the CH4 solutions, but with a few sites in southern Africa as well, such as Amersfoort (South Africa). The multi-species optimal network design solutions tended to have sites more evenly spread-out, but concentrated the placement of new tall-tower stations in Africa between 10ºN and 25ºS. The uncertainty reduction achieved by the multi-species network of twelve stations reached 47.8% for CO2, 34.3% for CH4, and 32.5% for N2O. The gains in uncertainty reduction diminished as stations were added to the solution, with an expected maximum of less than 60%. A reduction in the absolute uncertainty in African GHG emissions requires these additional measurement stations, as well as additional constraint from an integrated GHG observatory and a reduction in uncertainty in the prior biogenic fluxes in tropical Africa.

Ten months into the Covid-19 pandemic it remains unclear whether transmission of SARS-CoV-2 is affected by climate factors. Using a dynamic epidemiological model with Covid-19 climate sensitivity in the likely range, we demonstrate why attempts to detect a climate signal in Covid-19 have thus far been inconclusive. Then we formulate a novel methodology based on susceptible-infected time trajectories that can be used to test for seasonal climate sensitivity in observed Covid-19 infection data. We show that if the disease does have a substantial seasonal dependence, and herd immunity is not established during the first peak season of the outbreak (or a vaccine does not become available), there is likely to be a seasonality-sensitive second wave of infections about one year after the initial outbreak. In regions where non-pharmaceutical control has contained the disease in the first year of outbreak and thus kept a large portion of the population susceptible, the second wave may be substantially larger in amplitude than the first if control measures are relaxed. This is simply because it develops under the favorable conditions of a full autumn to winter period and from a larger pool of infected individuals.

Background: The science–policy interface process – known as a ‘scientific assessment’ – has risen to prominence in the past few decades. Complex assessments are appropriate for issues which are both technically complicated, multifaceted and of high societal interest. There is increasing interest from the research community that studies biological invasions to undertake such an assessment. Objectives: Providing the relevant background and context, the article describes key principles and steps for designing, planning, resourcing and executing such a process, as well as providing evidence of high-impact assessments enhancing scientific careers. Method: Experience from international and national assessments, most recently the South African scientific assessment for the Shale Gas Development in the Central Karoo, was used to develop this guiding generic template for practitioners. Analyses of researcher publication performances were undertaken to determine the benefit of being involved in assessments. Results: The key success factors for assessments mostly relate to adherence to ‘process’ and ‘governance’ aspects, for which scientists are sometimes ill-equipped. As regards publication outputs, authors involved in assessment processes demonstrated higher H-indices than their environmental scientist peers. We have suggested causal explanations for this. Conclusion: Effectively designed and managed assessments provide the platform for the ‘co-production of knowledge’ – an iterative and collaborative process involving scientists, stakeholders and policymakers. This increases scientific impact in the society–policy domain. While scientists seem concerned that effort directed towards assessments comes at the detriment of scientific credibility and productivity, we have presented data that suggest the opposite.

Grasslands, which represent around 40% of the terrestrial area, are mostly located in arid and semi-arid zones. Semiarid ecosystems in Africa have been identified as being particularly vulnerable to the impacts of increased human pressure on land, as well as enhanced climate variability. Grasslands are indeed very responsive to variations in precipitation. This study evaluates the sensitivity of the grassland ecosystem to precipitation variability in space and time, by identifying the factors controlling this response, based on monthly precipitation data from Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) and the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) data from the Multi-angle Imaging SpectroRadiometer-High Resolution (MISR-HR) datasets, used as proxy for productivity, at 60 grassland sites in South Africa. Our results show that MISR-HR products adequately capture the spatial and temporal variability in productivity at scales that are relevant to this study, and they are therefore a good tool to study climate change impacts on ecosystem at small spatial scales over large spatial and temporal domains. We show that combining several determinants and accounting for legacies improves our ability to understand patterns, identify areas of vulnerability, and predict the future of grassland productivity. Mean annual precipitation is a good predictor of mean grassland productivity. The grasslands with a mean annual rainfall above about 530 mm have a different functional response to those receiving less than that amount of rain, on average. On the more arid and less fertile soils, large inter-annual variability reduces productivity. Our study suggests that grasslands on the more marginal soils are the most vulnerable to climate change.

For a number of years, the extensive ecosystems of southern Africa have been a testing ground for ideas and techniques useful for studying and managing large-scale complex systems everywhere, and in particular for tackling issues of global change. The first contribution has been through making consistent, long-term, large-scale observations on climate, vegetation and animal dynamics and disturbances. These have been crucial in developing and testing hypotheses regarding how the earth system works at large space and timescales. The observational techniques have evolved dramatically over time: from notes kept by individuals, to systematic measurement programmes by organisations, to continuous and sophisticated measurements made by automated systems such as satellites and flux towers. The second contribution has been experimental, developing the notion that ecosystems can be the subject of deliberate experimental manipulation. Sometimes this has taken the form of large-scale treatments, such as fire trials or herbivore exclusion plots. More frequently, it has made use of the ‘experiment’ of the protected area in contrast to its surrounds, or has exploited the information in natural or human-induced gradients. Ecosystem experimentation has required rethinking the fundamentals of experimental design: What is the experimental unit? What is the meaning of a control? What constitutes replication? The third contribution has been theoretical. How does the functioning of warm, dry, species-rich ecosystems differ from the cool, moist, species-poor ecosystem examples that dominate the literature? What are the roles of disturbance and competition is maintaining ecosystem diversity, and top-down versus bottom-up control in maintaining ecosystem structure? The fourth contribution concerns the management of large-scale complex systems in the face of limited knowledge. How can the gap between science and policy be narrowed? What advantages and challenges does participatory co-management offer? How do you implement adaptive management?