Rainy season characteristics with reference to maize production for the Luvuvhu river catchment, Limpopo Province, South Africa.

Abstract

In arid and semi-arid regions, crop yields are mainly dependent on the amount and spatio-temporal distribution of rainfall. For most smallholder farmers in rural areas of southern Africa, rainfall is a critical input to agricultural production of most staple crops such as maize. To effectively plan for agricultural development, it is of utmost importance that the spatial distribution and temporal variation of rainfall is understood as it govern the type of farming systems that can be practiced in any region. Therefore, a detailed understanding of rainfall is necessary before any farming activities can commence. The study investigated rainy season characteristics with reference to maize production in the Luvuvhu River Catchment. Rainy season characteristics assessed included aridity index, onset, cessation, length of the season, false onset, dry spells, seasonal rainfall, number of rainy days and monthly rainfall. Historical daily rainfall and minimum and maximum air temperature data (1923-2015) were obtained from the Agricultural Research Council. Twelve meteorological stations that were evenly distributed and represented different climatic regions within the catchment were chosen. An aridity index for different areas of the catchment was calculated using the United Nations Environment Programme equation. Evapotranspiration was calculated using the Hargreaves and Samani equation. Annual rainfall was calculated by summing daily rainfall from 1st January to 31st December. The Instat+ v 3.36 statistical programme was utilized to calculate onset, cessation, and length of the season, the number of rainy days, dry spells, seasonal rainfall and monthly rainfall. The Statistica software was used to generate descriptive statistics as well as to calculate probability of exceedance and non-exceedance for the rainy season characteristics. The Anderson-Darling goodness of fit test was performed to determine the distribution model that best represents the data. The resultant probabilities of exceedance were then computed from the distribution models that best fit the data. A non-parametric Spearman rank correlation coefficient test was used to analyze data for trends in rainy season characteristics as well as monthly rainfall. The results from the study showed that monthly rainfall at the Luvuvhu River Catchment during the rainy season varies temporally and spatially. In the high rainfall areas of the catchment, the rainy season commences early from the third week of October and ends the first week of April the following year. For dry areas of the catchment, the rainy season commences in the second week of November and ends early in the third week of February. The results further show a decrease in length of the rainy season, the number of rainy days, and seasonal rainfall further away from wet to dry areas of the catchment. There was no significant change on the onset of the rainy season on the catchment for the past 27-90 years. There is a high risk of both short and medium dry spells at most stations during the month of October, with, Folovhodwe, Phafuri and Sigonde being at highest risk. Farmers are therefore advised to use the first onset for land preparation and plant after the second onset in November and December to avoid the high risk of dry spells and false onset in October and November, depending on the location at the catchment. Folovhodwe, Mampakuil, Phafuri and Sigonde have a mean length of rainy season of less than 120 days and seasonal rainfall of less than 500 mm per rainy season. Hence, these areas are not suitable for rain-fed maize in the current climate. However, they are suitable for the production of other crops which may be sold in order to purchase maize. The most favourable sites for maize production within the catchment are Entabeni, Levubu, Lwamondo, Thathe, Tshiombo, and Vreemedeling. Therefore, production should be maximized at these areas so that there is sufficient maize for the whole catchment. In dry years, stations situated in the low-lying areas in the north-eastern and eastern parts of the catchments receive less rainfall which does not permit planting of maize. In normal and wet years, rainfall is sufficient for the production of various crops. However, in semi-arid areas of the catchment, plans should be made for supplementary water due to high evapotranspiration rates in order to maximize maize production. Stations in the middle/south western parts of the catchment can receive significant rainfall in both dry, normal and wet years. Trend analysis for long-term rainfall data did not show any significant changes in monthly rainfall except for Lwamondo and Levubu where an increasing trend is notable in January rainfall. In December, the rainfall trend was significant at Entabeni, Folovhodwe and Lwamondo. An increase in rainfall is notable at Lwamondo and a decrease in rainfall at Entabeni and Folovhodwe.