This study is based on the numerical analysis of the properties of routinely observed hydrometeorological data which in South Africa alone is collected at a rate of more than half a million station days per year, with some records approaching 100 continuous years in length. The analysis of this data demonstrates an unequivocal synchronous linkage between these processes in South Africa and elsewhere, and solar activity. This confirms observations and reports by others in many countries during the past 150 years. It is also shown with a high degree of assurance that there is a synchronous linkage between the statistically significant, 21-year periodicity in these processes and the acceleration and deceleration of the sun as it moves through galactic space. Despite a diligent search, no evidence could be found of trends in the data that could be attributed to human activities.
It is essential that this information be accommodated in water resource development and operation procedures in the years ahead.