## 3 Results
### Water Requirements of Japanese Plum Orchards
The observations from both studies suggest the need for better orchard management and water-saving practices in South Africa compared to Spain. However, further research on the plum water requirements in South Africa, particularly those of high-density orchards (>1000 trees ha\({}^{-1}\)), is required for a more comprehensive assessment. Recently, [PERSON] and [PERSON] [57] estimated the ET rates over a 307,000 km\({}^{2}\) agricultural plain in California. The average ET for plums was estimated to be 994 mm a\({}^{-1}\) with a standard deviation of 188 mm a\({}^{-1}\), whilst the cumulative water consumption between 2017 and 2019 was estimated to be 4.1 km\({}^{3}\) (accounting for 0.65% of total water use across the study area). The remotely sensed estimates were validated using a network of eddy covariance flux towers, yielding coefficient of determination (R\({}^{2}\)), Root Mean Square Error (RMSE) and average marginal effect (AME) values of 0.82, 11.53 mm month\({}^{-1}\) and 9.56, respectively. [PERSON] et al. [58] estimated the ET rates over a 70 km\({}^{2}\) stretch of land in Chile's agriculturally prominent O'Higgins region. The daily ET estimates for the plum orchards ranged between 3 and 5 mm day\({}^{-1}\). The actual and reference ET (ETo) for the season were estimated to be 331 and 525 mm, respectively. The remotely sensed estimates had a good agreement with the ground-based ET values, producing RMSE and bias values of 0.6 mm day\({}^{-1}\) and \(-\)0.4 mm day\({}^{-1}\), respectively. The low ET estimate reported in the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Reference Location** & **Method** & **Cultivar** & **Water Use (mm a\({}^{-1}\))** & **Water Use (mm season\({}^{-1}\))** & **Key Findings** \\ \hline \hline
[14] & Spain & FAO-56 Kc & Black Gold & 432–525 & The RDI strategy allowed for 30\% water savings, increasing the tree water use efficiency with minimal effect on crop yield and fruit growth, providing that the plant water stress during the fruit growth period was low (stem water potential \(>-1.5\) MPa). & The proposed open-source system aims to improve the assessment of ET and water productivity and the management of water resources. & It is possible to estimate evapotranspiration using a Normalized Difference Vegetation Index (NDVI) time series by integrating data from Landsat 8 and Sentinel-2 sensors, improving irrigation water management at the plot and water distribution system scales. Accurate estimation of crop water requirements attracts potential water savings of up to 20\% in certain situations. These results apply a very localized level. Western Cape farmers, compared to those internationally, show that they are two to nine times more efficient in their water use during fruit production than the international water footprint averages suggest. & It is possible to estimate evapotranspiration using a Normalized Difference Vegetation Index (NDVI) time series by integrating data from Landsat 8 and Sentinel-2 sensors, improving irrigation water management at the plot and water distribution system scales. Accurate estimation of crop water requirements attracts potential water savings of up to 20\% in certain situations. These results apply a very localized level. Western Cape farmers, compared to those internationally, show that they are two to nine times more efficient in their water use during fruit production than the international water footprint averages suggest. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._study was attributed to a water deficit during the season resulting from poor irrigation management in the area. The study also had a shorter growing season of 3 months (December-March), compared to 5-6 months in the other studies. Growing season length appeared to be the most common cause of discrepancies in the water requirement estimates. Late-season-maturing orchards have a longer growing season, meaning the trees retain their leaves for longer.