91 research outputs found

    Protocol of an individual participant data meta-analysis to quantify the impact of high ambient temperatures on maternal and child health in Africa (HE 2 AT IPD)

    Get PDF
    Introduction: Globally, recognition is growing of the harmful impacts of high ambient temperatures (heat) on health in pregnant women and children. There remain, however, major evidence gaps on the extent to which heat increases the risks for adverse health outcomes, and how this varies between settings. Evidence gaps are especially large in Africa. We will conduct an individual participant data (IPD) meta-analysis to quantify the impacts of heat on maternal and child health in sub-Saharan Africa. A detailed understanding and quantification of linkages between heat, and maternal and child health is essential for developing solutions to this critical research and policy area. Methods and analysis: We will use IPD from existing, large, longitudinal trial and cohort studies, on pregnant women and children from sub-Saharan Africa. We will systematically identify eligible studies through a mapping review, searching data repositories, and suggestions from experts. IPD will be acquired from data repositories, or through collaboration with data providers. Existing satellite imagery, climate reanalysis data, and station-based weather observations will be used to quantify weather and environmental exposures. IPD will be recoded and harmonised before being linked with climate, environmental, and socioeconomic data by location and time. Adopting a one-stage and two-stage meta-analysis method, analytical models such as time-to-event analysis, generalised additive models, and machine learning approaches will be employed to quantify associations between exposure to heat and adverse maternal and child health outcomes. Ethics and dissemination: The study has been approved by ethics committees. There is minimal risk to study participants. Participant privacy is protected through the anonymisation of data for analysis, secure data transfer and restricted access. Findings will be disseminated through conferences, journal publications, related policy and research fora, and data may be shared in accordance with data sharing policies of the National Institutes of Health. PROSPERO registration number: CRD42022346068

    Diversity and Ranking of ENSO Impacts along the Eastern Seaboard of Subtropical Southern Africa

    Get PDF
    El Nino–Southern Oscillation (ENSO) is the dominant mode of interannual climate variability over southern Africa during the summer half of the year. It is widely accepted that El Nino (La Nina) core summers (December–February) are typically warmer and drier (cooler and wetter) than average over the region. Although it is recognized that the ENSO impacts are nonlinear and not all events result in the expected impact, little or no work has been carried out to systematically explore the diversity and ranking of these impacts. Here, parameter-space bubble plots involving various rainfall and temperature metrics are used to study how such impacts vary over the eastern seaboard of subtropical southern Africa to determine the ENSO events with the strongest impacts, and to identify the most anomalous ENSO cases. Comparison of neutral summers experiencing the strongest droughts/floods with ENSO impacts is also performed. These metrics are designed to be applicable to the interests of farmers and other user groups. It is found that 1987/1988 (2017/2018) was the most unusual El Nino (La Nina) and neutral 1981/1982 had a severe drought, worse than occurs during most El Ninos. These unusual cases are explained in terms of regional circulation and SST anomalies. Implications of the results for seasonal forecasting and for farmers are discussed

    Diversity and Ranking of ENSO Impacts along the Eastern Seaboard of Subtropical Southern Africa

    No full text
    El Niño–Southern Oscillation (ENSO) is the dominant mode of interannual climate variability over southern Africa during the summer half of the year. It is widely accepted that El Niño (La Niña) core summers (December–February) are typically warmer and drier (cooler and wetter) than average over the region. Although it is recognized that the ENSO impacts are nonlinear and not all events result in the expected impact, little or no work has been carried out to systematically explore the diversity and ranking of these impacts. Here, parameter-space bubble plots involving various rainfall and temperature metrics are used to study how such impacts vary over the eastern seaboard of subtropical southern Africa to determine the ENSO events with the strongest impacts, and to identify the most anomalous ENSO cases. Comparison of neutral summers experiencing the strongest droughts/floods with ENSO impacts is also performed. These metrics are designed to be applicable to the interests of farmers and other user groups. It is found that 1987/1988 (2017/2018) was the most unusual El Niño (La Niña) and neutral 1981/1982 had a severe drought, worse than occurs during most El Niños. These unusual cases are explained in terms of regional circulation and SST anomalies. Implications of the results for seasonal forecasting and for farmers are discussed

    Representation of the Mozambique channel trough and its link to southern African rainfall in CMIP6 models

    Get PDF
    The topography of Madagascar and the strength of the Mozambique Channel Trough (MCT) modulate summer rainfall over southern Africa. A strong MCT hinders the penetration of moisture bearing easterlies from the South Indian Ocean into the mainland, thus reducing rainfall there and vice versa for weak MCT summers. Given the link between the MCT and rainfall, it is important to analyse how climate models represent the trough. Here, output from 20 models within the CMIP6 ensemble of Coupled General Circulation Models (CGCMs) are analyzed to investigate how state-of-the-art CGCMs represent the MCT and its link to southern African rainfall. Overall, the ensemble mean insignificantly underestimates the observed MCT. There is a large spread among the models, with the strength of the MCT significantly correlated with the Froude number based on the mountain height over Madagascar. In models, the vorticity tendency in the MCT area is dominated by the stretching and friction terms, whereas the vertical advection, tilting and residual terms dominate in the ERA5 reanalysis. The link between MCT and rainfall in the southern African subcontinent is missing in the models. Large rainfall biases are depicted over mainland even in models with a very strong MCT. It is found that the impacts of the MCT in the models could be masked by a complex mix of processes such as the strength of the Angola low, moisture fluxes from the Indian and South Atlantic Oceans as well as overestimated convection in the Mozambique Channel area.Representation of the Mozambique channel trough and its link to southern African rainfall in CMIP6 modelspublishedVersio

    Inter‐annual variability of the along‐shore Lagrangian transport success in the southern Benguela Current upwelling system

    No full text
    A 3-km resolution regional ocean model is used to investigate the role of wind-driven coastal circulation and mesoscale variability on the inter-annual variability of transport success in the southern Benguela between Cape Point (34°S) and St Helena Bay (32°S) from 1992 to 2011. Lagrangian particles are released within the top 100 m of the water column along an across-shore transect off Cape Point. Transport success is given by the ratio of the number of particles that reach St Helena Bay over the total number of particles released. The analysis of transport success anomalies and their relationship with the local circulation and wind forcing reveal that there is no single driver of the inter-annual variability. The transport success variability of particles released on the shelf (depths 500 m), across-shore transports induced by mesoscale eddies are the main contributors to transport success variability. Rare passage of Agulhas rings near the shelf edge can induce strong offshore advection of particles into the open ocean. In contrast, shelf-edge cyclonic eddies favour the onshore transport of particles originating from the outer shelf-edge and thus contribute to increase transport success. Plain Language Summary This study investigates the inter-annual variation of Lagrangian transport in the southern Benguela Current upwelling system using a high-resolution regional ocean model and particle tracking experiments. Transport of fish eggs and larvae by upper ocean currents is crucial for the marine ecosystem in this highly productive region since the spawning and nursery areas used by anchovies are separated by large distances ( ∼400 km). The alongshore connectivity between the Cape Peninsula and St Helena Bay from 1992 to 2011 is analysed and linked to the regional ocean circulation and wind-forcing on an inter-annual time scale. We find that transport success is influenced by several drivers including the Benguela Jet, Ekman transport, the coastal inner-shelf poleward counter-current, and occasional interactions with eddies such as Agulhas rings and shelf-edge cyclonic eddies. These findings provide a valuable information for the future studies on the role of the physical drivers that impact transport of larvae and eggs in the southern Benguela, underlining that no single driver can account solely for extreme positive or negative events in transport success

    A climatology of drylines in the interior of subtropical Southern Africa

    No full text
    DATA AVAILABILITY STATEMENT : The ERA5 data (Hersbach. et al. 2018) used were downloaded from the Copernicus Climate Change Service (C3S) Climate Data Store. Satellite imagery was downloaded from EUMETSAT Data Store. Station data in this study are available on request from the South AfricanWeather Service (SAWS) (http://www.weathersa. co.za). Other surface observation data were downloaded from online (www.ogimet.com), as were monthly ERSSTv5 data for the Ni ˜no-3.4 region (Huang et al. 2017) (https://climexp. knmi.nl/).A climatology of synoptic drylines on the subtropical southern African interior plateau (SAP) is developed using ERA5 reanalysis specific humidity and surface temperature gradients and an objective detection algorithm. Drylines are found to occur regularly during spring and summer (September–March), and almost daily during December of that period, but rarely in winter. A westward shift in peak dryline frequency takes place through the summer. Drylines peak first over the eastern parts of the SAP during November with a mean of 10 drylines and then over the central (mean of 12) and western SAP (mean of 20) in December. During midsummer, drylines over the eastern SAP are negatively correlated with drylines in the west. Between 1980 and 2020, a significant correlation exists between ENSO and dryline days over the eastern (r = 0.44; p value = 0.004) and central (r = 0.41; p value = 0.008) SAP with fewer drylines (up to 10) occurring during years with increased surface moisture and more drylines (up to 45) occurring during years with decreased surface moisture. Drylines forming over the eastern parts of the SAP were more likely to move westward than drylines over the central and western parts. Onset times across the SAP show that drylines have a tendency to form during either the late morning to early afternoon (1100 and 1400 LST) or during the early evening hours (1700 and 2000 LST), suggesting that the surface heat trough (Kalahari heat low) and westward moisture transport mechanisms, such as the Limpopo low-level jet and ridging highs, are responsible for the formation of most drylines across the SAP.South African National Research Foundation (NRF) ACSyS Programme and the FLAIR programme, a partnership between the African Academy of Sciences and the Royal Society funded by the U.K. Government’s Global Challenges Research Fund.https://journals.ametsoc.org/view/journals/clim/clim-overview.xmlam2023Geography, Geoinformatics and MeteorologySDG-13:Climate actio

    Two types of ridging South Atlantic Ocean anticyclones over South Africa and the associated dynamical processes

    No full text
    Using 41 years of ERA5 reanalysis, two types of ridging South Atlantic Ocean high pressure systems were identified in the South African domain. Type-N events have a zonal structure and the ridging component breaks off from the parent South Atlantic Ocean anticyclone, after extending across the South African mainland. Type-S events extend south of the mainland and then break off. The Type-N (Type-S) ridging component is weaker (stronger) leaving behind a stronger (weaker) South Atlantic Ocean high. The two types of ridging events are associated with different configurations of Rossby wave packets that propagate across the South Atlantic Ocean. Surface and upper tropospheric anomalies associated with Type-S wave packets are stronger than those associated with Type-N events and the vertical coupling of the anomalies is much stronger during Type-S events. Type-N events are associated with a double jet streak structure, with the downstream jet contributing to upward motion over the landmass by means of its thermally direct circulation at its jet entrance. The upstream jet during Type-N events induces downward motion over the southern half of South Africa as it propagates eastward. The Type-S upstream jet streak, which only appears during winter, has limited zonal extent and does not induce downward motion over the country. Type-N ridging is associated with stronger ageostrophic moisture fluxes along the southern coast leading to higher moisture content and precipitation along the south eastern and eastern coasts of South Africa.The Water Research Commission, South Africahttp://www.elsevier.com/locate/atmoshj2021Geography, Geoinformatics and Meteorolog

    April 2022 Floods over East Coast South Africa: Interactions between a Mesoscale Convective System and a Coastal Meso-Low

    No full text
    Extreme rainfall occurred over the South African east coast during 10–12 April 2022, leading to over 500 deaths and massive damage. This study seeks to understand a key feature, namely the progression of the rainfall maxima from the northern KwaZulu-Natal (KZN) coast during the night of 10–11 April by ~550 km to the Eastern Cape coast about 48 h later. The large-scale circulation was dominated by a cut-off low over the South African interior with a strong ridging anticyclone southeast of the country in the South Indian Ocean. Satellite, rain gauge, and ERA5 reanalysis are used to show that the timing and location of the heaviest rainfall are closely tied to, firstly, the formation of a Mesoscale Convective System (MCS) at ~0300UTC April 11 on the northern KZN coast which tracked south and then offshore, and secondly, a meso-trough which formed a coastal meso-low by ~2100 UTC April 11. The meso-low tracked south over the warm waters of the Agulhas Current before strengthening into Subtropical Depression Issa. Mesoscale interaction between the MCS and coastal meso-low determined the positioning and timing of the strongest onshore low-level jet, moisture convergence and uplift, and hence the progression of the heavy rainfall down the coast. Such mesoscale interaction has not previously been documented in southern Africa or the Southern Hemisphere

    Investigating the global impacts of the Agulhas current

    No full text
    The Agulhas Current is the major western boundary current of the Southern Hemisphere [Lutjeharms, 2006] and a key component of the global ocean "conveyor" circulation controlling the return flow to the Atlantic Ocean [Gordon, 1986]. As such, it is increasingly recognized as a key player in ocean thermohaline circulation, with importance for the meridional overturning circulation (MOC) of the Atlantic Ocean. Unusual dynamics pervade the motion of this warm-water current-as it moves west around the southern tip of Africa, it is retroflected back east by the Antarctic Circumpolar Current. Not all waters are captured by this sudden diversion of course-parts of the Agulhas Current leak away into the South Atlantic Ocean (Figure 1)
    • …
    corecore