CHAPTER 2: LITERATURE REVIEW
2.5 Meteorological disasters
2.5.2 Floods
Floods are defined as an overflow that comes from a river or other body of water and causes or threatens damage (Chapman, 1994; Smith, 2004), in other words, any relatively high streamflow overtopping the natural or artificial banks in any reach of a stream (Smith, 2004).
Floods are regarded as the most common natural disasters in both developed and developing countries (Smith, 1999). Floods are mainly caused by excessive rainfall. Other causes of floods include ice melt, ice jam, landslides, dam failures, storms, and tsunamis (Figure 2.4) (Smith, 2004). Floods can cause damage to life, livelihoods and environment (van Zyl, 2006). From 1980-2010 there have been 77 flood events in South Africa with Eastern Cape, KwaZulu-Natal, North West and Limpopo province being the most vulnerable provinces to flooding (Zuma et al., 2012). The probability of flooding occurring in any given year in South Africa is 83.3 % (Zuma et al., 2012). Floods are part of the earth natural hydrologic cycle and can occur anywhere in the world anytime. Of all types of disasters, floods are the most damaging and demanding of all types of natural disasters (Smith, 2001). Floods can be described according to the water source origin, geography of receiving area, cause and the speed of onset (Smith, 2004). There are different types of floods, namely flash, river, coastal and urban (Figure 2.4).
18 Table 2.1 Primary and secondary impacts of droughts (Source: Vogel et al., 1999)
Primary impacts Secondary impacts
SOCIAL
Disrupted distribution of water resources Migration, resettlement, conflicts between water users Increased quest for water Increased conflicts between water users
Marginal lands become unsustainable Poverty, unemployment
Reduced grazing quality and crop yields Overstocking; reduced quality of living
Employment lay-offs Reduced or no income
Increased food insecurity Malnutrition and famine; civil strife and conflict Increased pollutant concentrations Public health risks
Inequitable drought relief Social unrest, distrust
Increased forest and range fires Increased threat to human and animal life Increased urbanization Social pressure reduced safety
ENVIRONMENTAL
Increased damage to natural habitats Loss of biodiversity
Reduced forest, crop, and rangeland productivity Reduced income and food shortages Reduced water levels Lower accessibility to water
Reduced cloud cover Plant scorching
Increased daytime temperature Increased fire hazard Increased evapotranspiration Crop withering and dying
More dust and sandstorms Increased soil erosion; increased air pollution Decreased soil productivity Desertification and soil degradation (topsoil erosion) Decreased water resources Lack of water for feeding and drinking
Reduced water quality More waterborne diseases
ECONOMIC
Reduced business with retailers Increased prices for farming commodities
Food and energy shortages Drastic price increases; expensive imports/substitutes Loss of crops for food and income Increased expense of buying food, loss of income Reduction of livestock quality Sale of livestock at reduced market price
Water scarcity Increased transport costs
Loss of jobs, income, and property Deepening poverty; increased unemployment Less income from tourism and recreation Increased capital shortfall
Forced financial loans Increased debt; increased credit risk for financial institutions
19 Figure 2.4 The physical causes of floods in relation to other environmental hazards (Source: Smith, 2004)
2.5.2.1 Impacts of flooding
Flooding and its impacts continue to threaten most parts of the developed and developing world, and is viewed as the most frequent and catastrophic disaster that affects human settlements, infrastructures and farming in the flood prone areas (Nelson, 2004). The impacts of flooding vary temporally, spatially, economically, culturally and politically (Johnson, 2003).
Impact severity depends on many factors such as physical setting, uses and socio economic status (Johnson, 2003). However, flooding often has significant, damaging effects on agricultural production. The impacts of flooding can either be classified as direct or indirect (Gommes and Negre, 1992). Directs impacts of flooding are those that affect property, income of individual, enterprises and the public sector e.g., loss of life and crops due to flooding (Gommes and Negre, 1992). Indirect impacts of flooding take long and are more widespread geographically and economically, they result from decreased income, environmental degradation and other factors (Gommes and Negre, 1992). The impacts of flooding differ depending on the time of occurrence. Floods can either occur during the growing season or non-growing period (Johnson, 2003). The impacts of flooding during the growing and non- growing period are shown in Table 2.2.
Physical causes of floods
River floods
Atmospheric hazards
Rainfall Snowmelt Ice jam
Tectonic hazards
Landslides
Technologica l Hazards
Dam Failures
Coastal floods
Atmospheric hazards
Storm surges
Tectonic hazards
Tsunamis
20 Table 2.2 The impacts of floods during the growing and non-growing period (Source:
Johnson, 2003)
Non-growing seasons Growing seasons
Loss of top soil Waterlogging of crops
Loss of soil nutrient Lodging of standing crops
Soil compaction Loss of soil nutrient
Soil erosion Loss of soil pasture use
Deposition of undesirable materials Soil erosion Permanent damage to perennial crops, trees,
livestock, buildings and machinery
Greater susceptibility to diseases and insects Displacement of persons Interruptions to tillage, planting, crop
management and harvesting Breakage of levees and other retention
structures
Permanent damage to perennial crops, trees,livestock, buildings and machinery Anaerobic processes Soil temperature reduction and/or retardation Permanent cessation of farming in
floodplains
Necessity of installation of expensive drainage systems
Permanent diversion /realignment of rivers, streams and other bodies of water and settlements
Loss of livestock and/or habitat Loss of livestock and/or habitat Grain spoilage, in field and off-site
Transportation interruptions
Feedback effect, enhancing precipitation due to large, free-water evaporative surfaces