Climate of the Limpopo River Basin: Drought

Drought is the most common and devastating of all environmental affecting the Limpopo basin, with impacts felt in economic, social and environmental terms (Leira et al 2002; FAO 2004).  Variable and erratic rainfall means that the rainy season often does not start when expected and can be episodic, with an entire season’s rainfall occurring in the space of a few days.

Drought Hazard Index

One measure of drought risk is Drought Hazard Index (DHI), which focuses on the probability of crop failure combined with the degree of rainfall variability.  Relative DHI for the Limpopo River basin is illustrated in the map below.  Low DHI indicates a relatively low chance of crop failure, and High indicates an increased probability of crop failure, due mainly to rainfall variability. 

The northern bank of the Limpopo River in Botswana, Zimbabwe and Mozambique, appears to be more susceptible than the northern bank in the South African portion.

Drought Vulnerability in the Limpopo River basin

IFAD (1996) and Benson et al. (1997) suggest that approximately 60 % of the southern African region is vulnerable to drought, with 30 % highly vulnerable. The Leira et al 2002 for Disaster Preparedness and Response in the Limpopo Basin (Leira et al 2002) suggests that droughts in the region occur every 7 to 11 years.  FAO (2004) states that extreme droughts occur in the basin every 10 to 20 years.

The drought of 1991–92 was the most severe in recent history, affecting the entire southern Africa region including the Limpopo River basin. Although there are strong indications that drought occurs cyclically in southern Africa, it is not yet possible to predict these events with a high degree of certainty. Scientists have discovered a relationship between the El Niño Southern Oscillation (ENSO) and drought in southern Africa, but the correlation is not strong. In terms of hydrological drought, a mixed positive and negative correlation between the warm ENSO events and the quarterly seasonal river runoff in southern African Rivers has been reported (Alemaw and Chaoka 2006).

Recent studies have shown that the occurrence of droughts is closely linked to the see-saw of El-Niño events and La- Niña conditions over southern Africa from December to February.  These changes are illustrated in the diagram below.  In most, but not all cases, El Niño events cause unusually dry and warm conditions in southern Africa during the December to February months, whereas La Niña events bring unusually wet and cool conditions to the region for the same period.

Impacts of Drought

Drought is often seen as simply an agricultural and food supply issue (FAO 2004), but studies have shown (Benson and Clay 1998; Vogel, Laing and Monnik 1999) that the impacts of droughts are far-reaching, with signficant economic, environmental and social impacts. The table below, adapted from Vogel, Laing and Monnik (1999), summarises the impacts of drought in South Africa, but FAO (2004) assert that these issues are relevant to drought vulnerable areas across all of southern Africa.

Impacts of drought in southern Africa.

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 range land 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