Leveraging remote sensing for optimised national scale agricultural water management in South Africa

Agriculture remains a critical water resources consumer in arid regions, globally, including southern Africa. The intensity of consumption, however, varies significantly depending on the adopted watering method (i.e., rainfed or irrigated) and agricultural region. Efficient agricultural water management hinges on effectively monitoring Crop Water Use (CWU) and Crop Water Productivity (CWP). This study, thus, leveraged Moderate Resolution Imaging Spectroradiometer (MODIS) remotely sensed data in estimating the spatio-temporal variations of CWP and CWU across irrigated and rainfed croplands in diverse South African agricultural regions between 2017 and 2022. The results showed that rainfed croplands had higher CWU in agricultural regions dominated by grains (150 mm/yr) and cattle (160 mm/yr), while irrigated croplands exhibited the highest CWU in agricultural regions with sheep rearing (175 mm/yr) and subsistence agricultural activities (160 mm/yr). However, there were no significant differences (p > 0.05) in overall CWU across all the agricultural regions. Irrigated croplands generally had higher annual CWP (>0.002 kg/mm³/yr), while rainfed croplands consistently showed low CWP especially in forestry (0.001 kg/mm³/yr) and sugar (0.0012 kg/mm³/yr) agricultural regions. There were also no significant differences in average CWP between irrigated and rainfed croplands (p > 0.05). This study demonstrates the effectiveness of national-scale remotely sensed data in monitoring the spatiotemporal variations of CWP and CWU in South Africa. The results can be used to tailor strategies to specific agricultural regions and crop types and optimise water use efficiency. This would contribute significantly to sustainable national-scale agricultural water management in South Africa.