Stefan Grab

Stefan Grab
University of the Witwatersrand | wits · School of Geography, Archaeology & Environmental Studies

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172
Publications
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Publications

Publications (172)
Article
Full-text available
This study evaluates precipitation trends in the upper Mzingwane sub-catchment (UMS) of Zimbabwe using ten World Meteorological Organization (WMO)’s Expert Team for Climate Change Detection Monitoring and Indices climate indices. Trend analysis for variables such as annual total precipitation, extremely wet days, consecutive wet and dry days is ana...
Article
The Agulhas Current (AC) off the southern tip of Africa is one of the strongest western boundary currents and a crucial choke point of inter-ocean heat and salt exchange between the Indian Ocean and the southern Atlantic Ocean. However, large uncertainties remain concerning the sea surface temperature (SST) and salinity (SSS) variability in the AC...
Article
We introduce the Dutch East India Company ‘day registers’ as one of the world’s longest known pre-19th Century corporate chronicles (1652-1791) containing near-continuous, systematic, non-instrumental daily weather information for Cape Town, southern Africa. This transcript provides the longest known continuous 17 th /18 th Century daily weather re...
Article
Full-text available
The generation of index-based series of meteorological phenomena, derived from narrative descriptions of weather and climate in historical documentary sources, is a common method to reconstruct past climatic variability and effectively extend the instrumental record. This study is the first to explicitly examine the degree of inter-rater variabilit...
Article
It is now well established that global to local climate is impacted by volcanic forcing associated with major eruptions. Much attention has been given to the way in which climate is affected by such eruptions, particularly for the Northern Hemisphere, and to a considerably lesser extent for the Southern Hemisphere. Research knowledge gaps remain on...
Article
Full-text available
Although global and Northern Hemisphere temperature responses to volcanic forcing have been extensively investigated, knowledge of such responses over Southern Hemisphere continental regions is still limited. Here we use an ensemble of CMIP5 models to explore Southern Hemisphere temperature responses to four major volcanic eruptions: Krakatau (1883...
Book
This edited book is based on the papers accepted for presentation during the 2nd Springer Conference of the Arabian Journal of Geosciences (CAJG-2), Tunisia, in 2019. Major subjects treated in the book include geomorphology, sedimentology, and geochemistry. The book presents an updated unique view in conjugating field studies and modeling to better...
Preprint
Full-text available
The generation of index-based series of meteorological phenomena, derived from narrative descriptions of weather and climate in historical documentary sources, is a common method to reconstruct past climatic variability. This study is the first to explicitly examine the degree of inter-rater variability in producing such series, a potential source...
Article
Full-text available
The northernmost Limpopo Province is located in one of the warmest regions of South Africa, where the agricultural sector is prone to heat stress. The aim of this study was to explore air temperature and relative humidity trends for the region, which have implications for agricultural adaptation and management (amongst other sectors). In particular...
Preprint
Full-text available
The Agulhas Current (AC) off the southern tip of Africa is one of the strongest western boundary currents and a crucial chokepoint of inter-ocean heat and salt exchange between the Indian and the South Atlantic Ocean. However, large uncertainties remain concerning the sea surface temperature and salinity variability in the AC region and their drivi...
Article
Full-text available
The increasing expansion of urban environments with associated transformation of land-cover has led to the formation of urban heat islands (UHI) in many urbanized regions worldwide. COVID-19 related environmental impacts, through reduced urban activities, is worthy of investigation as it may demonstrate human capacity to manage UHI. We aim to estab...
Article
A range of social and economic factors impact tree species, such as Sclerocarya birrea subsp. caffra (marula), which provide livelihood sustenance for local communities in the savanna woodlands of southern Africa. As an ecologically important savanna species, valued both culturally and economically, it is imperative to understand if resource use is...
Article
Rural farming households in developing countries frequently contend with multiple challenges, including a lack of resources, food insecurity, and poverty. Climate change threatens to compound existing challenges, particularly in such rural subsistence economies with limited adaptive capacity. We aim to establish farmers' perspectives on likely impa...
Article
Although volcanic forcing impacts on climate have gained much international attention during recent years, focus has largely been at hemispheric scale, and most particularly on the Northern Hemisphere (NH). Here we investigate the impact of major volcanic eruptions since 1883 on southern African climate, with a view to establishing potential sub‐re...
Preprint
Full-text available
This study evaluates precipitation trends in the upper Mzingwane sub-catchment (UMS) of Zimbabwe for the variables of annual precipitation, extremely wet days, consecutive wet days and consecutive dry days. The UMS is of strategic socio-economic significance in terms of its provision of water security and sustenance to livelihoods. The analysis is...
Article
Full-text available
Southern Africa sits at the junction of tropical and temperate systems, leading to the formation of seasonal precipitation zones. Understanding late Quaternary paleoclimatic change in this vulnerable region is hampered by a lack of available, reliably-dated records. Here we present a sequence from a well-stratified sedimentary infill occupying a lo...
Preprint
Full-text available
Although global and Northern Hemisphere (NH) temperature responses to volcanic forcing have been extensively investigated, knowledge of such responses over Southern Hemisphere (SH) continental regions is still limited. Here we use an ensemble of CMIP5 models to explore SH temperature responses to four major volcanic eruptions: Krakatau (1883), Sant...
Article
Full-text available
Here, we aim to establish possible morphogenetic associations between periglacial phenomena (sorted circles and turf-/stone-banked lobes) by examining (a) rock surface weathering rinds by thin section microscopy and SEM-EDX analysis, and (b) alpine shrub growth patterns of Helichrysum trilineatum supported by AMS 14 C age determination. The study a...
Article
Full-text available
Agricultural activities are considered the most important source of income for ~ 23% of the population in Mazandaran Province, Iran. However, farming activities are overwhelmingly exposed to the detrimental impacts of drought in this region. The purpose of this paper is to establish differences in farmers’ perceptions on the effects of drought on s...
Article
Surface pressure observations are invaluable for meteorological investigations as they enable reconstructions of and insights to historical large-scale tropo-spheric circulation. This article endeavours to use a daily reduced mean sea level pressure (MSLP) series to reconstruct the monthly frequency of cold fronts, associated with mid-latitude cycl...
Article
Studies have demonstrated that plant phenophases (e.g. budburst, flowering, ripening) are occurring increasingly earlier in the season across diverse ecologies globally. Despite much interest that climate change impacts have on coffee (Coffea arabica), relatively little is known about the driving factors determining its phenophases. Using high-reso...
Article
Full-text available
Plain Language Summary Climate is affected by major volcanic eruptions if the eruption emits large amounts of SO2 into the stratosphere. Volcanic forcing generally causes temperatures to cool, but in some instances, temperatures rise. Many studies have identified Northern Hemisphere (NH) climatic responses to volcanic forcing, but the Southern Hemi...
Article
Full-text available
In this study, the wet-bulb globe temperature (WBGT) validated biometeorological index is used to monitor and project future human thermal stress in Iran. The meteorological components required to calculate this index include dry and wet temperatures, relative humidity and radiation. To monitor and project thermal stress, data for two time periods...
Article
Full-text available
Limited research has focussed on historical droughts during the pre-instrumental weather-recording period in semi-arid to arid human-inhabited environments. Here we describe the unique nature of droughts over semi-arid central Namibia (southern Africa) between 1850 and 1920. More particularly, our intention is to establish temporal shifts in influe...
Article
Full-text available
The study evaluated CORDEX RCMs’ ability to project future rainfall and extreme events in the Mzingwane catchment using an ensemble average of three RCMs (RCA4, REMO2009 and CRCM5). Model validation employed the statistical mean and Pearson correlation, while trends in projected rainfall and number of rainy days were computed using the Mann-Kendall...
Article
Full-text available
Improving scientific knowledge of volcanic eruptions and their impact on climate is important for testing and improving climate projection models. Despite substantive work on the impacts of major volcanic eruptions on global to regional scale climate, most studies have focussed on the northern hemisphere, with little information available for the s...
Article
Subaerial physical, chemical and biological weathering processes are significant contributors to mountain landscape development worldwide, and over long time scales. This paper reports on pseudokarst features formed by different subaerial weathering processes on a high-elevation basalt plateau surface in the Maloti–Drakensberg mountains of eastern...
Article
Understanding the historical dynamics of wildlife distribution and abundance is essential to developing appropriate conservation measures. Here we investigate the occurrence and status of medium-to large-sized fauna (excluding avifauna) for the mountain Kingdom of Lesotho and immediate adjoining regions of South Africa, from the late Pleistocene to...
Article
Full-text available
Rainfall characteristics during the annual rainy season are explored for the Mzingwane catchment of south-western Zimbabwe, for both historic period (1886–1906) and more recent times (1950–2015), based on available daily and monthly precipitation series. Annual and seasonal rainfall trends are determined using the modified Mann-Kendall test, magnit...
Article
Full-text available
A global inventory of early instrumental meteorological measurements is compiled that comprises thousands of mostly nondigitized series, pointing to the potential of weather data rescue.
Article
The rainfall series from the South African Astronomical Observatory in Cape Town, South Africa, is one of the longest known single site instrumental records in the southern hemisphere, spanning over 176 years. Rainfall data are analysed to determine trends and periodicity in the series for annual, seasonal and monthly time scales. Using the Mann Ke...
Article
Full-text available
This study demonstrates that Hadley cell dynamics could be used as a proxy to determine cloud cover and thus solar energy potential over South Africa. Granger causality was used to investigate causal interactions between the Hadley cell and cloud cover for the period 1980–2015, and such links were established. Areas of strong causality are found ov...
Article
Full-text available
Climate change has the potential to alter the spatio-temporal distribution of rainfall, subsequently affecting the supply and demand of water resources. In a water-stressed country such as South Africa, this effect has significant consequences. To this end, we investigated annual and winter rainfall and river flow trends for the Western Cape Provin...
Article
Full-text available
Limited research has focussed on historical droughts during the pre-instrumental weather-recording period in semi-arid to arid human-inhabited environments. Here we describe the unique nature of droughts over semi-arid central Namibia (southern Africa) between 1850 and 1920. More particularly, our intention is to establish temporal shifts of influe...
Article
Full-text available
Instrumental meteorological measurements from periods prior to the start of national weather services are designated “early instrumental data.” They have played an important role in climate research as they allow daily to decadal variability and changes of temperature, pressure, and precipitation, including extremes, to be addressed. Early instrume...
Article
Full-text available
Phenological shifts represent one of the most robust bioindicators of climate change. While considerable multidecadal records of plant and animal phenology exist for the northern hemisphere, few noteworthy records are available for the southern hemisphere. We present one of the first phenological records of fish migration for the southern hemispher...
Article
Full-text available
Temperature trends for KwaZulu-Natal (KZN), South Africa, are investigated for the period 1930–2015, with the intention to test whether interior regions (within ~ 100 km of the coast) are warming faster than coastal regions, given oceanic moderating effects along the coast. This is achieved through analyzing instrumental temperature records from th...
Article
Full-text available
Single- to multiple-year drought episodes posed significant challenges for agrarian communities across southern Africa during the nineteenth century and hence are widely recorded in a variety of historical documents. However, the ways in which droughts are articulated, and the focus of individual accounts, vary considerably between different author...
Article
Using composite analysis, the timing and extent of El Niño–Southern Oscillation (ENSO) impacts on maximum (Tmax) and minimum temperatures (Tmin) during austral summer are investigated for South Africa over the period 1940–2016. Pearson correlation coefficients determined between temperature data at stations within regions indicate that temperature...
Article
The eastern Lesotho highlands are of considerable hydrological importance to southern Africa as a so-called ‘water tower’ for the surrounding region. Here, we contribute proxy-data inferring climate and vegetation changes over the past 1600 years, assessing in parallel inorganic and organic chemical analyses on a sediment core from Ladybird wetland...
Article
Full-text available
The Paris Agreement achieved in December 2015 established that the signatory countries should pursue to hold the increase in global average temperature to below 2 °C relative to the preindustrial period and to strive to limit the temperature increase to 1.5 °C below the preindustrial period. The potential changes in tropical cyclones over the basin...
Article
Full-text available
Compared to other types of livestock, poultry is widely owned by rural households in developing countries. Rural poultry production is not a primary agricultural activity per se, but rather serves to supplement other farming activities in resource-poor rural communities, and thus contributes significantly as a source of scarce animal protein and in...
Article
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Parts of eastern Africa have experienced substantial climatic variability and extremes during the last few decades. Here we explore the extent to which local place-based knowledge is used and is relevant to understanding and appropriately responding to place-based climate variability and change (specifically rainfall) in an area of considerable rai...
Article
Full-text available
In the Drakensberg Range of eastern Lesotho, periglacial sorted circles, stone-banked and turf-banked lobes, blockfields, block streams and wetland thúfur (earth hummocks) are present. These features are of varying ages (likely from Last Glacial Maximum to contemporary) and have been disturbed by soil formation and vegetation growth. This study use...
Article
Recent and historical austral summer and winter rainfall characteristics have been widely investigated across southern Africa. However, a notable gap of knowledge remains for the Namibian region. This article presents the first extensive 19th century (1845–1900) hydro-climate history for central Namibia, derived from documentary evidence. Unpublish...
Article
Full-text available
Globally, droughts are a recurring major natural disaster owing to below normal precipitation, and are occasionally associated with high temperatures, which together negatively impact upon human health and social, economic, and cultural activities. Drought early warning and monitoring is thus essential for reducing such potential impacts on society...
Article
Full-text available
Stomatal regulation is a key process in the physiology of Coffea arabica (C. arabica). Intrinsically linked to photosynthesis and water relations, it provides insights into the plant's adaptive capacity, survival and growth. The ability to rapidly quantify this parameter for C. arabica under different agroecological systems would be an indispensabl...
Article
Atmospheric warming and extreme weather events have increasingly become major contemporary issues of global concern, yet relatively few studies have investigated recent decadal-scale climate change and variability in Zimbabwe. This study investigates spatiotemporal temperature and extreme weather events in Mzingwane catchment of southern Zimbabwe f...
Article
Full-text available
Over recent decades, concern has been raised regarding the management of Chrysocoma ciliata L. (Asteraceae syn. C. tenuifolia) in the eastern Lesotho Highlands. This shrub species is argued to be a Karroid invasive introduced anthropogenically within the last century. Historical botanical records in Lesotho are scarce, so the origins of this specie...
Article
Spatio-temporal dynamics of near-surface wind speeds were examined across the Northern, Western and Eastern Cape regions of South Africa. The regions assessed were geographically subdivided into three zones: coastal, coastal hinterland and inland. Wind speed data (10 m) were evaluated at monthly, seasonal, annual and zonal resolutions, with the aim...
Article
Full-text available
Present-day drainage patterns in mountain regions are strongly affected by antecedent tectonic and geologic factors. In the mountains of eastern Lesotho, southern Africa, bedrock comprises flat-lying Jurassic basalts which have given rise to a relatively uniform initial land surface. Here, we present key morphometric measurements of river drainage...
Conference Paper
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Landfills produce pollutants that negatively impact humans and the environment. In developing countries such as South Africa, landfilling is the most common form of solid waste management. People living in close proximity to landfills are particularly at risk to harmful pollutants such as volatile organic compounds (VOCs). Although VOCs only consti...
Article
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We present attributes of snow occurrence and dissipation rates (melt and sublimation) for the Lesotho Highlands, based on remotely-sensed MODIS images from 2003–2016. Multi-temporal imagery is used, with SNOMAP and NDSI algorithms applied to MODIS Rapid Response images. The spatial extent of snow loss was determined by daily repeat measurements of...
Article
Southern African late Quaternary research has developed rapidly during recent decades, with an increase in the range of proxies used, the inclusion of new field sites, and increased international collaboration and skills transfer. This has enabled recent meta-studies into the synoptic drivers of palaeoenvironmental shifts across the region, and of...
Article
The eastern Lesotho Highlands experience climate patterns distinct from those of surrounding lower altitude regions, representing a niche environment with a unique biodiversity, leading to well-adapted but restricted vegetation. This study explores changes in the Holocene composition of diatoms and pollen at southern Africa’s highest altitude wetla...
Article
The eastern Lesotho Highlands host an array of periglacial and glacial geomorphic features. Their analysis has provided past climate interpretations predominantly for cold periods, yet no multi-proxy temporally continuous palaeoenvironmental records exist. This study presents a palaeoenvironmental reconstruction based on sedimentary characteristics...
Article
To establish precise climate trend analyses, highly reliable and accurate homogenous historical climate data are required. To this end, we undertake a robust quality control and homogenization process of daily Tmax and Tmin data (1916–2013) for the Western Cape Province, South Africa, using RClimDex, ProClimDB and Anclim software. Inhomogeneities w...
Article
Lesotho provides a unique context for palaeoclimatic research. The small country is entirely landlocked by South Africa, yet has considerable variation in topography, climate, and associated vegetation over an approximate east–west transect. The region has been of archaeological interest for over a century, and hosts many Early to Late Stone Age si...
Article
Geomorphology plays a pivotal role in linking the traditional subdisciplines of physical geography. This is because geomorphological processes are influenced by climate, and geomorphology in turn strongly controls land surface hydrology and ecosystems. This review assesses the current status of geomorphology in South Africa. Six subfields are ident...
Article
Climate change and variability are pervasive contemporary realities in Africa. In this paper, we investigate climate stressors (i.e. rainfall patterns and drought) that have occurred in the Great Ruaha River sub-Basin (GRRB), Tanzania. By making use of a mixed-methods approach, including both quantitative and qualitative data collection, we demonst...