## Water Consumption at the Basin Scale and Trends in WUE
### WUE and Water Consumption at the Basin Scale
Figure 4: Area of land in the Unites States irrigated using different methods. (Plotted from data obtained from: USDA 1990, Table 4; USDA 1999, Table 4; USDA 2006, Table 4.6.1; USDA 2009, Table 4; USDA 2014, Table 28) [46]. Figure 5: Total irrigation water use in Australia. (Plotted from data obtained from: Australian Bureau of Statistics (ABS), 2004–2018.) While Figure 5 shows the trend of irrigation water use in the whole of Australia, Figure 6 is specific to the MDB, which consumes the bulk of the water used for irrigation in the country as previously discussed. In addition, Figure 5 shows the trend of the irrigated land in the basin and correlation of the irrigation water use with the area irrigated, meaning when farmers have access to more water, they irrigate more land (and vice versa). Therefore, it is likely that water saved as a result of the water-efficient technologies and practices adopted is reused as suggested by the studies quoted above. However, there are strategies that can be used to attain a good balance between improved irrigation efficiency and environmental conservation, including groundwater recharge. A typical example is the water saving initiatives funded by the Australian Government, with the understanding that the water saved is released for environmental use [6]. The regulatory return of the saved water to the environment therefore mitigates the \"rebound effect\" phenomenon, which suggests that the increase in efficiency of use of a resource may lead to an increase in the rate of consumption of that resource [48]. Many other studies undertaken in different parts of the world have also linked widespread adoption of water-efficient technologies to overall increase in water consumption mostly due to expansion of land under irrigation, and not a decrease as intended. Nonetheless, as shown by a study undertaken in Spain, the water-efficient technologies have come with other side benefits such as reduced use of fertilisers and better accounting of water use [49]. In the literature reviewed for this study, an almost unanimous view that emerges is that overall reduction of water at the basin scale cannot simply be attained through the promotion or subsidies provided for water-efficient technologies. These technologies will thus need to be used in tandem with other measures such as incentives for conservation [45] and regulations to limit water allocation [44], among others. Another interesting dimension is the nexus between the irrigation methods deemed to be generally more water-efficient, energy consumption and greenhouse gas emissions. For instance, modelling has demonstrated that although pressurised irrigation systems such as sprinkler and drip methods are generally more efficient and productive, they are more energy-consuming (compared to conventional systems such as furrow irrigation), resulting in the production of additional greenhouse gas emissions [50]. The energy costs in many countries (in the case of irrigation electricity for pumping  
Figure 6: Irrigation water use and area irrigated (’1000 ha) in the Murray Darling Basin, Australia. (Plotted from data obtained from: ABS 2004–2018.) water) has been rising steadily. This is thus likely to impact on the adoption of the water-efficient but high-energy consuming irrigation methods.