**4. Discussion**

There is great uncertainty about the future effects of climate change on crop production. This analysis explores the potential implications of climate change on catchment crop yield based on CORDEX-RCM driven by six GCMs for two IPCC emission scenarios (RCP 4.5 and RCP 8.5). Furthermore, four possible adaptation strategies to cope with climate change impact in the Olifants catchment were considered: the combination of changing sowing date and application of full irrigation, application of rainwater harvesting, adoption of the deficit irrigation method, and the use of efficient irrigation devices.

Our analysis revealed an increased warming trend of between 1 ◦C to 5 ◦C for both climate change scenarios (RCP 4.5 and RCP 8.5) relative to the baseline climate of 1976–2005. This analysis aligns with the predictions of Durand [8]. On the other hand, average monthly precipitation is expected to decrease in the future for both climate change scenarios with the exception of the month of August and September for RCP 4.5 during the early term. This finding aligns with Kusangaya et al. [48] who also predicted decreased precipitation over Southern Africa. The changes in precipitation and temperature, particularly in the summer months when crops are being planted, have caused significant declines in crop yield. Such decreases are mostly attributed to increased temperature [17,20,21,49]. Contrary to this

finding, a study by Cazadilla et al. [9] found an increase in crop production for South Africa under the MIROC AIB scenario. However, this contradiction may be due to the uncertainty associated with global climate models.

Considering the negative impacts of climate change on crop production in this study, we evaluated different adaptation strategies to improve crop production. Among the adaptation strategies assessed, the integration of changing sowing date with full irrigation application had the highest crop yield under both current and projected climate change scenarios as compared to other adaptation strategies evaluated. The adoption of changing sowing date alone might not be an effective measure to cope with climate change considering the significant decline in the catchment precipitation. However, few studies [50,51] have observed an increase in crop yield with the adoption of this strategy.

Combining changing sowing date with the application of full irrigation is seen to be an effective measure to cope with the long-term impact of climate change, but the application of full irrigation might prove to be challenging, as the Olifants catchment is already experiencing water stress arising from increased demands. The adoption of rainwater harvesting is therefore seen as an effective measure towards resolving this challenge as it involves harvesting rainwater from runoffs during periods of heavy rainfall. This approach would thus reduce the over-exploitation of fresh water from the system during irrigation. Our analysis has shown that the application of rainwater harvesting would improve the yield of crops under current and projected climate change which is consistent with the findings of Lebel et al. [52] and Rasuiba [53]. Contrary to the findings of the study conducted by Chimonyo et al. [54], where the application of the deficit irrigation method improved the yield of sorghum and cowpea plant, our experiments provided a different result. However, our findings aligned with the findings of a study by Shrestha L and Shrestha N [55] who also reported a decline in winter wheat yield with the adoption of the deficit irrigation approach. The application of an efficient irrigation device improved the yield of maize crops while the yield of other studied crops remained unchanged under current and projected climate change.

Findings from this study have shown that not all adaptive measures are capable of improving crop yield under the impact of climate change. It is therefore important to evaluate crop response to different adaptation measures before implementation in order to determine the most suitable and appropriate strategies to be adopted.
