*3.4. Climate Change Impact on Crop Water Requirement*

This study assessed the impacts of climate change on crop water requirements by integrating climate parameters into the WEAP-MABIA crop model. Table 4 shows the projected changes in crop water requirements for RCP 4.5 and RCP 8.5 climate change scenarios. Results revealed a steady increase in crop water requirements for both RCPs. Water requirements for maize crops increased from 7.6 × 108 m3 for the baseline climate to 9.1 × <sup>10</sup><sup>8</sup> m3 and 1.0 × <sup>10</sup><sup>9</sup> <sup>m</sup>3, while soya beans increased from 2.2 × 108 <sup>m</sup><sup>3</sup> to 3.1 × <sup>10</sup><sup>8</sup> <sup>m</sup><sup>3</sup> and 3.6 × 108 <sup>m</sup><sup>3</sup> for RCP 4.5 and RCP 8.5 climate change scenarios. An increase of 1.4 × 108 m3 and 7.3 × 107 <sup>m</sup>3, 1.6 × 108 m3, and 9.1 × 107 <sup>m</sup><sup>3</sup> was anticipated for dry beans and sunflower for both RCPs relative to 9.3 × <sup>10</sup><sup>7</sup> m3 and 4.3 × <sup>10</sup><sup>7</sup> <sup>m</sup><sup>3</sup> of baseline climate. Comparing both RCPs, a slight decrease in water requirements for maize and soya beans was expected under RCP 8.5 in the early term, with the highest water requirements for all crops expected towards the end of the century. The increased water requirements for all crops modeled in the WEAP-MABIA crop model is due to the high evapotranspiration rate resulting from an increased temperature and a decline in precipitation. Water stress can only occur when rainfall or irrigation do not meet crop water requirements. Therefore, the simulated results for crop water requirements show that crops in the Olifants catchment will likely face severe water stress in the future which may lead to a decline in crop yield.

**Table 4.** Future changes in crop water requirements (in m3) for RCP 4.5 and RCP 8.5 climate change scenarios relative to baseline climate.

