Results & Discussion
Trends in mean annual average temperature
The mean annual average temperature (MAT) was analyzed using emmeans as shown in Fig 5 to account for missing data which uses a regression mixed model using the year and region as the predictor variables and MAT as the response [out1 = lmer(MAT~YEAR*CLIMZONE+(1|STATION_ID))]. The syntax estimates the MAT using the fixed effects of the year and climatic zone while accounting for the random effect of the station.
The analysis showed that the Savanna, Sub-tropical, Desert and Equatorial generally had a higher MAT ranging between 21°C and 26 °C than the Steppe, Mediterranean and Bushveld of MAT range 15°C and 21°C. The differences in temperature could be explained by a number of factors. The continental layout over the Equator and the Tropics of Cancer and Capricon make the continent generally have higher temperatures all year round. The cooler temperatures of the Mediterranean, Steppe, and Bushveld can be explained by the influence of the sea and occurrence in the intertropical convergence zone that hail cooling currents over the southern landscape. The northern Mediterranean is equally influenced by the Mediterranean sea above the continent.
All the zones showed an increasing temperature after the year 1975 a rapid change that has partially been attributed to human-induced climate change as a result of increasing greenhouse gases such as carbon dioxide, and methane among others in the atmosphere (IPCC, 2022).
Fig 6: A bubble plot map showing the rate of change in climate in °C per decade (SLOPE10) at each station using values of the mean annual average temperature.
Fig 6 represents the decadal changes in temperature for each region developed with rounded-off grids to reduce their joining.
The regions closer to the midriff or Equator experienced less change a trend that change moving outwards of the equator. The zones of Mediterranean and Bushveld and Steppe showed increasing temperatures over the years.
Trends in total annual precipitation
The total annual precipitation (TAP) varied for the different climatic zones (Fig. 7) with the Equatorial having the highest TAP ranging 1400-1900 mm a feature attributed to its vast rainforests of the Congo and west Africa. The Sub-tropical region also experienced high precipitation attributed to the vegetation such as the Miombo woodlands that stretch across south and eastern Africa and the local influences of water bodies and mountains that characterize this landscape (Ribeiro et al., 2015; Wilson & Primack, 2019) .
The Steppe registers the lowest TAP presumably due to the maritime air mass that stays offshore thus hindering rain formation. This situation is not shared by the Mediterraneans as they receive winter cyclones that induce precipitation in the regions (Britannica, 2022).
Generally, the regions do not display any evident changes in precipitation over the years of study perhaps due to the coarseness of the regions used in this study as increased precipitation has been reported in montane areas of East Africa and reduced predipitation in the Sahara desert of north Africa and the drylands of Eastern Africa (IPCC, 2021).