The spatial and temporal variability of climatic conditions is fundamental to agricultural and natural resource management (Hartkamp et al. 1999). Perhaps equality important is the variability of the precipitation, particularly with respect to human use and attempts to manage the resource. For example, knowledge of when rainfall is likely to occur is critical for water resource management planning (Mishra 1991) and for agricultural productivity. Furthermore, it has a significant impact on food security, as high variability results in high levels of uncertainty.
Areas with predictable, consistent rainfall have been able to proceed with agricultural and municipal development with stable water inputs. Regions that suffer from highly variable precipitation are subject to equal levels of uncertainty, meaning that development proceeds with greater risk from drought and/or flood.
In addition to directly impacting rainfed agriculture, climate variability requires increased storage capacity in dams to enable a constant yield to users. The southern African region is subject to abundant solar radiation, therefore high inter-annual variability of rainfall becomes the main determinant of crop yields (Lumsden and Schulze 2005).
Climate of the Limpopo River Basin: Climatic Patterns
Coefficient of Variation of Rainfall
One method for determining variability of precipitation is the calculation of the Coefficient of Variation of rainfall (CV%). This coefficient is calculated as the standard deviation divided by the mean to allow comparisons of rainfall variability (Commonwealth of Australia 2006). Schulze (2006) defines the CV(%) as "a relative measure of dispersion, as it facilitates relative comparisons of variability in that it takes account of the magnitude of the mean and is independent of the original unit of measure in being expressed as a percentage".
In the Zimbabwean portion of the basin, the CV% is approximately 40 %, with the probability of > 500 mm/yr of precipitation being < 60 % in the southern highveld, < 30 in the southern lowveld and < 10 % in the area around Beitbridge (near the border with South Africa (FAO 2004). While there are some localised coefficient of variation data available for specific areas (as above), there is currently no basin-wide assessment of CV% available.
The map below is a preliminary estimate of CV% for the Limpopo River basin, based upon mean monthly precipitation data obtained from FAO (2000).
CV% FOR THE LIMPOPO RIVER BASIN. SOURCE: HATFIELD 2010/FAO 2000
Temperature Variability
The maps below show average temperatures for different seasons in the basin. The image on the left illustrates the average temperatures for January (summer) and the image on the right is July (winter).
The temperature variation in the eastern portion of the basin is considerably lower than the west, with winter temperatures in the northern Drakensberg mountains falling to as low as 2 °C.
AVERAGES DAILY TEMPERATURES IN JANUARY. SOURCE: FAO 2000
MEAN ANNUAL EVAPOTRANSPIRATION FOR THE LIMPOPO RIVER BASIN. SOURCE: FAO
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