AN INTEGRATED EARLY WARNING FORECAST SYSTEM FOR WET SEASONS AND THEIR RELATIONSHIP TO FLOODING EVENTS: A PREDICTABILITY STUDY IN SUPPORT OF HYDROLOGICAL APPLICATIONS Report to the Water Research Commission by LE Mpheshea; FA Engelbrecht; AF Beraki; R Maisha; R Nkoana and J van der Merwe Council for Scientific and Industrial Research (CSIR) WRC Report No. 2522/1/18 ISBN 978-0-6392-0044-6 September 2018 Obtainable from: Water Research Commission Private Bag X03 Gezina, 0031
[email protected] or download from www.wrc.org.za DISCLAIMER This report has been reviewed by the Water Research Commission (WRC) and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the WRC, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. Printed in the Republic of South Africa © WATER RESEARCH COMMISSION ii EXECUTIVE SUMMARY Southern Africa, defined here as the landmass area enclosed between 22–35° S and 12–36° E, receives the bulk of its rainfall during the austral summer. Moreover, the region exhibits pronounced interannual rainfall variability linked to the teleconnected influence of sea surface temperature (SST) anomalies in the tropical Pacific Ocean. In events where anomalously positive (negative) SSTs are observed over the domain between 5° N and 5° S and between 120° W and 170° W, which is commonly referred to as the Niño 3.4 region, there tends to be higher (lower) than normal rainfall conditions over southern Africa. For the purpose of this project, the sub-region located in north-eastern South Africa [2–28° S; 24–33° E] is considered as the main focus area.