Abstract
The study assesses onset of rains, cessation of rains, duration of rainy season and seasonal rainfall at different probability levels. Daily rainfall data for 309 stations located in the Free State Province of South Africa were analysed from 1950 to 2008. The cumulative rainfall over 3 consecutive dekads (10-day periods) and cumulative rainfall over 1 dekad were used to determine onset of rains and cessation of rains respectively. Seasonal rainfall was determined as the accumulated rainfall from November to March. Rainbow statistical software was utilised to test for normality and determine probabilities at 20%, 50% and 80% risk levels. The other rainy season characteristics investigated were the probability of onset failure and probability of rainy season duration of less than 50, 100, 120 and 140 days. These rainy season indices were investigated in relation to maize production in the Free State. Rainfall behaviour during the growing period is one of the main limiting factors to rain-fed maize production, consequently influencing household food security. The results show that for onset of rains there is a large spatial variance over the Free State while cessation of rains shows small variance. There is also an east to west progression of onsets while the duration of the rainy season and seasonal rainfall also increased from west to east. Areas of low risk associated with rainy season characteristics are evident over the Thabo Mofutsanyane, eastern Motheo, eastern and northeastern Lejweleputswa and the Fezile Dabi districts, making these areas highly suitable for maize production. By contrast, high-risk areas are in the western and southern parts of the province and thus dryland maize production has low production potential in these areas.
Highlights
Rainfall is one of the weather elements which varies greatly on a spatial and temporal basis, impacting on agricultural activities (Mwale et al, 2004; Tveito et al, 2005; Moeletsi et al, 2011b)
According to Sivakumar (1990) and Mugulavai et al (2008), it is important to determine at a reasonable accuracy the probability levels of the onset of rains, cessation of rains and length of rainy period, as well as their inter-relationships, in order to assist in planning of dryland farming activities
Farmers aiming at planting maize for early markets can utilise earliest onset of rains occurring in September or October depending on the locality of the farm
Summary
Rainfall is one of the weather elements which varies greatly on a spatial and temporal basis, impacting on agricultural activities (Mwale et al, 2004; Tveito et al, 2005; Moeletsi et al, 2011b). According to Sivakumar (1990) and Mugulavai et al (2008), it is important to determine at a reasonable accuracy the probability levels of the onset of rains, cessation of rains and length of rainy period, as well as their inter-relationships, in order to assist in planning of dryland farming activities. Knowledge of the length and probable dates of the onset and cessation of the rainy season can help farmers choose the right cultivar suitable for their particular location or region (Tadross et al, 2005). Onset of rainfall is one of the most important occurrences to the farmer: earlier onset allows them to plough land and plant earlier and benefit from the lower evaporative demand, while later onset can cause the plant critical stages that are sensitive to water stress to be aligned with months of lower rainfall and higher evaporative demand, depending on location and timing of the onset of rains (Moeletsi et al, 2011a)
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