Framework for forecasting the extent and severity of drought in maize in the Free State Province of South Africa

Abstract

An effective framework for drought assessment requires a definition of drought severity, a weather-soils database for the relevant region in a geographic information system (GIS), a reliable crop growth model, a method of forecasting daily weather data from the present date till the end of the growing season and a mapping procedure for the graphical representation of a drought situation. The development and main features of such a framework (system) which is already in use in the Free State Province of South Africa, is described. Based upon the phase of the southern oscillation index, it has been applied to quantify and map drought hazard in maize by running maize crop growth models in a GIS. Input and output data for the latter are grouped in 9800 homogeneous natural resource zones. For each, computed maize grain yield forecasts are compared against long-term cumulative probability distribution functions of yield to determine their probabilities of non-exceedence and used to delimit drought severity areas accordingly. The system enjoys wide acceptance and credibility in the province. To date, the results have been well received by a rapidly growing number of users, now totalling 360. Major users are grain merchants, importers and exporters, millers, the provincial government and maize producers. No tests of accuracy of the forecasting system have been possible at this stage because the computation procedures and software have only just been completed. A similar project has, however, yielded promising results.