Inter-seasonal and intra-seasonal rainfall variability in the North West Province South Africa
The present study analysed inter-seasonal and intra-seasonal rainfall variability in the North West Province (NWP) South Africa. The observed rainfall data was obtained from South African Weather Service (SAWS) and Agricultural Research Council (ARC).The data used in the analysis covers a period of 31 rainfall seasons (1984 to 2015). The methodology used in the study to analyse rainfall variability was rainfall time series analysis while the rainfall trends were analysed using Man Kendall trend analysis and the Sens slope. Before evaluating rainfall variability in the province, NWP was classified into two homogeneous rainfall regimes using Cluster Analysis (CA). Cluster one (C1) covers central and southern stations while Cluster two (C2) covers the north-eastern stations in the province. The rainfall time series of the clusters show that C1 is increasing in aridity while in C2 the rainfall is showing an increase pattern. Mann Kendal trend test and Sens' slope estimator were used to study variability and trends in NWP rainfall. Trend analysis results of North West Province 1984-2015 seasonal rainfall indicated a general decrease in the province rainfall overtime. Four stations registered a statistically significant rainfall trend of which only one showed a negative rainfall trend. 9 out of 15 rainfall stations in C1 reported negative rainfall trend, while C2 is gradually becoming wetter with 82% of the stations showing a positive rainfall trend. In the intra-seasonal analysis, statistically significant stations (Delareyville, Taung, Olifantsport and Potchefstroom) were used. The results suggest that rainfall in North West Province shows a strong spatial and temporal variability at Intra-seasonal scale. Tendency towards aridity can be expected due to the delay and frequency of below normal rainfall experienced in NWP. The rainfall in the region can go for about 14 consecutive recording below normal events. While only few above normal rainfall pentads are recorded. However, some limitations (e.g., data length), were encountered in this study.
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