Keywords

1 Introduction

A hazard can be defined as any individual event or process that has potential to lead to loss or harm. Geological and environmental hazards are those events that arise from the workings of the natural environment, and as such they can be termed natural hazards . However, the term natural hazards is somewhat of a misnomer, as it could be argued that human activity has now impacted on almost all workings of the natural environment, and thus that all natural hazards are now substantially modified by human actions, either directly or indirectly (Bokwa 2013; Steffen et al. 2007). Geological and geomorphological hazards (contracted to the term geohazards ) are those that are related the operation of physical processes and/or events taking place on or within the Earth’s surface that have their origins in geological or geomorphological processes (Berger 2006). Environmental hazards are subtly different, because they include broader disturbance events taking place in different environments more generally, and affecting multiple elements of different environments. Environmental hazards are commonly those that relate to ecosystems and the hydrological cycle, and disturbance of the land surface. Commonly (but not always), geological hazards have a quick onset and environmental hazards have a slow onset. The most common geohazards and environmental hazards found globally, with particular examples from South Africa, are listed in Table 31.1. For simplicity, Table 31.1 distinguishes between different hazard types, but in many instances they are genetically related as an event cascade, or where the operation of one hazard increases the likelihood of another. For example, earthquakes commonly lead to landslides and debris flows (geological hazards). River floods caused by high rainfall can lead directly to soil erosion , water contamination and disruption of infrastructure; these can lead in turn to increased disease, poverty and societal vulnerability. There are of course many interconnections between different hazard types, and the different terms used for these hazard types unfortunately tend to conceal these interconnections. This may, in turn, undermine the efforts of managers and decision-makers to deal with the wide ranging impacts that hazards can have upon the physical and human environments.

Table 31.1 The range of typical geological and environmental hazards found in South Africa, with specific examples where appropriate
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Analysis of hazard types, their causes, risks and risk reduction strategies in South Africa, is also set within a wider international context. A key element includes the Sendai Framework for Disaster Risk Reduction (the latest version covering the time period 2015–2030). In South Africa, the National Disaster Management Centre (NDMC) deals specifically with coordination of hazards and disasters on national and provincial scales. The South African Risk and Vulnerability Atlas (SARVA 2008), developed in part by the NDMC, was an attempt to communicate the idea of risk and community vulnerability from different hazards to a wider audience. The atlas deals with risk factors of the physical and human environments that can lead to negative hazard impacts, and deals with issues of water resources, agriculture, coasts, biodiversity, and human health. In this context, geological and environmental hazards are the events that lead to potential disaster risk, and are thus explored in this chapter.

2 Hazards in South Africa

South Africa and sub-Saharan Africa more generally are particularly vulnerable to different hazard types, for a number of reasons (e.g. Alcántara-Ayala 2002). (1) The topography and relief of the land surface in South Africa vary spatially, with mountains and steep escarpments in some places and flat coastal plains in others. Geological hazards such as landslides and rockfalls are more likely in areas of high relief (Table 31.1). South Africa broadly has a semiarid climate and this therefore makes it sensitive to variations of precipitation, over different time scales (annual total, seasonal and event-scale). Precipitation also varies spatially, with different climate systems affecting the eastern and western parts of the country. Eastern areas are more likely to be affected by floods, and western areas by droughts. Such variations in precipitation also have associated negative impacts on agriculture and biodiversity, potable water availability, water quality, hydroelectric power production, sanitation and human health, food security and food prices, amongst others. (2) As a developing world country, South Africa has a high dependency on agriculture as part of its mixed economy, and in rural areas subsistence agriculture is vital for smallholder farmers. The dependence of many rural communities on agriculture makes them particularly vulnerable to climate changes and hydrological hazards. (3) South Africa’s population is in many cases poor, lacking political leverage, has low resilience and high vulnerability, has low social mobility, low education status, and is in some cases strongly gendered such that women (and indeed other groups) are disproportionately disadvantaged and thus more vulnerable to the effects of hazards (e.g. Akerkar and Fordham 2017). (4) South African society and governance has generally low adaptive capacity, and has low infrastructural resilience, to help cope with hazards and disasters. This has impacted on the capacity of national and regional governments, and other agencies and institutions, to respond effectively to hazards while they are in operation, and to plan for future events. National government and institutions have most influence on disaster management, but managing the impacts and reducing hazard risk is enacted mainly at the local level. Further discussion on disasters and risk management in South Africa is given in the chapter by Culwick.

3 Examples of Hazard Types in South Africa

Table 31.1 lists a range of geohazard and environmental hazard types, and examples from South Africa (where appropriate). Several examples of hazards are now described in more detail, illustrating the range of impacts on human and physical environments, and their interlinkages.

3.1 Floods as Climatic Hazards

Floods are a common hazard in South Africa. Apart from urban flash-flooding and coastal storm surges, the most widespread occurrences of floods result from high event-scale precipitation, in particular on the eastern side of the country, with incoming Indian Ocean cyclones during the austral summer (Alexander 1995). Many recent tropical cyclones have had significant negative impacts on both physical and human environments in northeast South Africa and adjacent areas of Zimbabwe and Mozambique. For example, Tropical Cyclone Dineo (February 2017) was a Category III Tropical Cyclone, and made landfall over southern Mozambique with sustained wind speeds of over 100 km/h and rainfall of <110 mm/day. In this region, official government figures report that 112,207 households and 548,566 people were affected, 33,014 houses were totally destroyed, and 7 deaths were incurred. High rainfall resulted in flooding from the Limpopo River , affecting surrounding communities and agricultural land (IFRC 2017). Previous tropical cyclones of a similar size have also caused significant damage and loss of life in this region, such as those in 2000 that claimed 800 victims in southern Mozambique, and 100 victims in 2015.

Instrumented flood hazard data are available from rivers in South Africa that show very clearly flood responses by different river systems. For example, the Sabie River has its source in high-precipitation areas of the Eastern Escarpment of South Africa, flowing eastward through the semiarid Lowveld to join the Incomati River system into the Indian Ocean. An extreme flood on the Sabie River (~7000 m3 s−1) took place in January 2012 following landfall of Tropical Cyclone Dando, and resulted in substantial net erosion along middle reaches of the river (Heritage et al. 2015). The Crocodile River, following the same direction as the Sabie and located in the same climate region, has experienced repeated seasonal flooding over the last decade, in particular in January of 2006, 2009 (Jan/Feb), 2011, 2012 and 2013, corresponding to high rainfall periods (Fig. 31.1). In February 2009, high rainfall resulted in high river discharge, with peak daily rainfall reaching 184 mm on 3 February within the Crocodile catchment. On 5 February 2009, the provincial government issued a flood alert for low lying areas. Communities and road users were warned to be careful when travelling. The floods caused extensive damage in communities and to infrastructure (Fig. 31.2a). In January 2012, seasonal flooding also took place along the Crocodile River. The highest peak daily rainfall was 210 mm (on 17 January 2012) (Fig. 31.1). A flood alert was issued on 19 January 2012 for residents in low lying areas (Fig. 31.2b). This flood resulted in significant erosion within the river system which caused the uprooting and transport of vegetation, and damage to infrastructure (Fig. 31.3). Economic impacts on the tourism sector were estimated at R58 million (Fitchett et al. 2016). Although most floods along river valleys or in lowlands are associated with high rainfall within river catchments, lower rainfall values over longer time periods can also lead to increased flood risk. Likewise, coastal flooding can take place without high rainfall being received. Despite these other situations that lead to flood hazards, climate model outcomes for South Africa projected to 2100 suggest that future rainfall will increase by 85–303 mm per year by 2100, the majority of which will fall during the austral summer months. The number of rain events is expected to increase, which may increase the likelihood of flood events, and increase streamflow variability (Schulze 2011).

Fig. 31.1
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(a) Daily rainfall record (mm) for weather station site X2E010, and (b) daily river discharge data (m3 s−1) for the Crocodile River from gauge station X2H006. Both sites are located within the Crocodile catchment. Both graphs show the period 1 August 2004–30 April 2014 inclusively; flood events in January/February 2009 and 2012 are highlighted by arrows. (Figure adapted from Sauka 2016)

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Fig. 31.2
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(a) Extract from a news report on the February 2009 flood along the Crocodile River (Source: ioL News 2009). (b) Extract from a media briefing by the Department of Water Affairs on the January 2012 flood. (Source: Mpumalanga Provincial Government website 2012. Figure adapted from Sauka 2016)

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Fig. 31.3
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Geomorphology and flood impacts on semi-arid rivers, northeast South Africa. (a, b) Sabie River between flood events, showing (a) sand bars amid bedrock outcrops, (b) shifting sand bars present within and alongside the active channel; (c) Sabie River in flood, where the river level is higher than bridge level (water flow from left to right), (d) same as (c), with more turbulent water flowing over a submerged bridge, with erosion on the down-flow side. Note the dirty colour of the water, which reflects the high sediment transport load, and the woody debris swept to either side of the channel, (e) flood marker on the Klaserie River, north of the Sabie. Note the woody debris trapped 4 m above the land surface in the branches of a tree (red arrow). This indicates the height of the flood, (f) flood impacts along the Sabie, including bank erosion and undercutting of settlements and agricultural land. (Photos a, b, e: Jasper Knight, c, d, f: Wikimedia Commons)

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3.2 Landslides and Other Land Surface Instabilities as Geological Hazards

In South Africa , landslides and other mass movements are concentrated in areas of steep and therefore unstable land surface slopes, and in particular in areas along the Great Escarpment edge in KwaZulu-Natal and Mpumalanga, and along the Cape Fold Belt mountains (Botha et al. 2016). Landslides and related instabilities such as rockfall , colluvial slope processes and soil erosion are known to have taken place throughout the Pleistocene and Holocene (Romer and Ferentinou 2016; Singh et al. 2008). A recent review by Botha et al. (2016) highlights the relationships between soil erosion due to land use change, colluvium deposition, and climate; examples of different types of land surface instabilities are shown in Fig. 31.4. More recently, studies have used remote sensing to map and monitor changes in the land surface environment, including the distribution of landslides (Diop et al. 2010) and gullies formed by soil erosion (Mararakanye and Le Roux 2012).

Fig. 31.4
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Examples of mass movement hazards in southern Africa. (a) Rock topple developed in basalts, eastern Lesotho; (b) translational landslides on the Great Escarpment edge, KwaZulu-Natal; (c) pervasive mass movement developed in slope sediments, KwaZulu-Natal, likely related to subsurface soil piping; (d) emergence of a bedrock ridge by progressive soil erosion from upslope to downslope, eastern Lesotho. (Photos: Jasper Knight)

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Thomas and van Schalkwyk (1993) described some of the varied impacts of slope failure caused by high rainfall and flooding in KwaZulu-Natal Province. For example, after storms in 1987–1988, 223 different slope failures were recorded on river valley sides in KwaZulu-Natal, largely associated with high rainfall and surface destabilisation but also due to river meander undercutting. Many of these failures took place in association with inappropriate geoengineering activities, including oversteepened and undrained slopes, blocked culverts, and along railway cuttings and embankments. Failure of river bridges took place by loss of structural integrity of surrounding rocks (17 cases directly, 16 cases indirectly), changes of river course (3 cases) or failure of bridge foundations (13 cases). Impacts of these slope failures included substantial structural damage to houses and roads especially around Durban where weathering of Natal Group sandstones results in cohesionless soils. Bell and Maud (2000) analysed the incidents of landslide failures around Durban associated with the 1987–1988 storms, and showed that small-scale landslides are likely to take place when event-scale rainfall exceeds 12% of mean annual rainfall, and major landslides where rainfall is over 20% of mean annual values .

3.3 Mining Impacts as Environmental Hazards

Mining for gold and other resources extracted from rocks of the Witwatersrand Basin, northern South Africa, has resulted in a range of different geological and environmental hazards. This includes formation of karstic sinkholes and collapse features (largely due to groundwater lowering), induced seismicity, particulate dust pollution, carbon monoxide and methane emissions, uncontrolled fires, and respiratory conditions such as silicosis amongst miners and in local communities (McCulloch 2009; Utembe et al. 2015). These different hazards operate over different spatial and temporal scales and thus their potential impacts on physical and human environments vary substantially. Acid mine drainage (AMD) is a common environmental hazard associated with mining. The chemical processing of mined ore, in order to extract metalliferous minerals, can result in high concentrations of mercury, arsenic, cyanide and other components in waste sediments and water. Contaminated waste water is often contained within storage ponds or biofiltered through wetlands on site, but may be lost through river outflow or by seepage into groundwater. Groundwater contamination is significant because it can spread underground for long distances, and affect potable water supplies. In addition, rainwater oxidation of pyrites within mine tailings dumps forms sulphuric acid which can cause the dissolution and transport of metals through the profile and into rivers, ponds and groundwater (McCarthy 2011). The result of this AMD is very low water pH, high sulphate concentration, low EH, and high electrical conductivity (Tutu et al. 2008). In river water, some metals are taken up in riparian vegetation, by the process of bioremediation, but contaminated water has a variety of negative impacts for environmental, biological and human health, largely by increasing toxicity levels within living tissue (Utembe et al. 2015). Furthermore, environmental degradation and contamination of land and water in mining regions negatively impact on the socioeconomic resilience of local communities, making them more vulnerable to be affected by future events (Naidoo 2015).

4 Discussion

Geological and environmental hazards that are common in South Africa have different origins, triggers, controls and dynamics, operate over different spatial and temporal scales, affect different environments, and have different types of impacts. These characteristics make it difficult to develop an overarching strategy to (1) monitor or evaluate potential hazards, or (2) deal with the varied potential impacts of hazards on human or physical environments. Furthermore, ongoing climate change is starting to have – and will increasingly do so in future – a role in amplifying the human and physical risk factors that contribute to greater vulnerability (Alcántara-Ayala 2002). Climate change scenarios for South Africa broadly suggest an increase of mean annual temperatures by 2–3 °C by 2100 (relative to the 1975–2005 mean), in particular with a warmer winter season (Li et al. 2013). For precipitation, most climate models predict wetter spring and summer seasons for the eastern interior of the country for the same time period, but drier elsewhere. Winter and in particular autumn seasons are predicted to become drier to 2100. The net effect is thus one of increased seasonality of rainfall by 2100, but its impact on annual precipitation totals is not clear, with some models predicting a net increase but most models a net decrease (Li et al. 2013). The models also suggest significant winter drying in the Western Cape region which lies within the winter rainfall zone . Although these model projections have been considered with respect to water resource availability and agriculture (Odiyo et al. 2015; Tadross et al. 2009), their implications for hazard types, magnitude, frequency and location are largely unknown. For example, changes in rainfall seasonality may lead to seasonal dryness and increased drought risk, whereas increased event-scale rain intensity may lead to increased flash-flooding . Such details are not captured by climate models and are thus an important area of future research.

A further confounding factor in hazard impact management is the role of the human environment. Many studies show that in developing world countries, different socioeconomic, educational, political and cultural factors can contribute to high vulnerability to be affected by different types of hazards (e.g. Adger et al. 2003; Shiferawa et al. 2014). In South Africa, there is also high socioeconomic and political inequality, which further disadvantages poor communities by weakening their adaptive capacity to climate change and climatic hazards in particular (Ziervogel et al. 2014). Thus, considering the physical causes or spatial/temporal patterns of hazards alone may not sufficiently capture their potential to impact human activity, either directly or indirectly. Projected increases in hazard frequency and/or magnitude due to climate change (e.g. Alfieri et al. 2017) can contribute to long-term environmental degradation and thus compromise sustainable development (Biggs et al. 2015). Understanding of the causes and effects of different hazards, and managing these effectively, therefore underpins national strategic development goals over the next decades and beyond.

5 Summary

Different hazard types and their varied impacts can act to have a multiplier effect on already-vulnerable communities in South Africa. Climatic hazards are already increasing in frequency and magnitude due to global warming, and this is likely to have significant secondary hazard impacts in South Africa through changing precipitation patterns, influencing future water and food security and environmental degradation. Although some hazards are better understood than others in terms of their forcing mechanisms and controls, it is still unclear how different hazards are interconnected or their relationships to human activity. This is an important area of future research for hazards and disaster risk in South Africa.