A three month stream flow forecast for water management in the upper Olifants catchment

A Climate Predictability Tool was used to evaluate the relationship between sea-surface temperatures and stream flow at different lead-times in the upper Olifants catchment in Mpumalanga, South Africa. Four stream flow stations were selected from each of the subcatchments of the upper Olifants, namely the Groot Olifants on the eastern side and the Wilger on the western side of the catchment. Canonical correlation analyses were used to make three month stream flow forecasts for October-November-December (OND) and January-February-March (JFM) seasons. Monthly global-scale SSTs were used to evaluate the effect of lead-times on correlations between global Sea-Surface Temperatures (SSTs) and stream flow. Then the lead-times with Pearson’s correlation values greater than 0.50 were selected to be used for evaluating possible origins of stream flow forecasting skill in the Equatorial Atlantic, Southern Atlantic, Equatorial Indian and Pacific Oceans. Although local climatic and hydrological characteristics were not considered in this study good hit score skill from the Southern Atlantic Ocean was found at a short lead-time of two months for both OND and JFM seasons. The equatorial Atlantic Ocean gave a good hit skill score at longer lead-times of seven and eight months. The equatorial Indian Ocean gave a higher Heidke score at a short lead-time of two months during OND and JFM seasons in the Groot Olifants sub-catchment. The oceanic domains adjacent to the southern African subcontinent gave a good Heidke score at a shorter lead-time as compared to the equatorial Pacific Ocean. These forecasts could be used for planning water storage and releases in dams that are down stream of these stream flow monitoring points.