Method
Solar Radiation
Solar radiation for any given location and time of year and day is influenced by five factors:
- astronomical;
- geographical (latitude and altitude);
- physical (scattering of solar radiation by atmospheric pollutants/aerosols and absorption mainly by water vapour);
- geometric (solar altitude and azimuth as well as slope steepness and aspect); and
- meteorological (cloudiness, type and thickness of the cloud, reflectivity).
From these five factors, daily estimates of solar radiation for 50 years were calculated at a 1.7 km resolution using equations developed and verified for South Africa (Schulze, 2008; Schulze and Chapman, 2008). The modelling for the intermediate future (2050s) was conducted using five different CMIP3 GCMs (Schulze et al. 2016).
More detail is provided in the section Background: Climate Change Modelling.
Maps
Map Information
In the following maps, means of historical daily solar radiation in MJ/m2 are presented together with their respective percentage changes from the present climatic conditions to the intermediate future (2050s). Maps are available for October (spring), January (summer), April (autumn) and July (winter).
The highest increases of the order of 3 MJ/m2 per day are projected for the transitional spring and autumn seasons as well as for winter (indicative of fewer cloudy days) while in the already sunny summer the projected increases are only ca. 1.5 MJ/m2 per day. The range of increases of ca. 1-4% is small to modest.
Across the region, solar radiation per se is seldom considered a limiting factor to crop growth and yield. The slightly increased solar radiation could have small effects at farm scale, influenced by slope and aspect (e.g. north- or south-facing), and could lead to small increases in potential evaporation and irrigation water demand.