Salinity-inclusive water scarcity: examples from food bowl regions of the US and Australia

Irrigated agriculture sustains more than 40% of global food production and uses up to 90 % of the world’s water resources. Water scarcity for the irrigation water use sector is a common problem, which may be driven by both water shortages and increased salinity levels. Limited studies however considered salinity issues in water scarcity assessment. We here developed a salinity-inclusive water scarcity framework for the irrigation sector, accounting for crop-specific irrigation water demands and salinity tolerance and its relation to water availability and salinity levels of both surface and groundwater resources. We assess temporal and spatial variation of water scarcity in agricultural river basins of the Central Valley (California) and the Murray Darling Basin (Australia), which are important food bowl regions. Our results show that including salinity and crop-specific salinity tolerances leads to very different water scarcity levels, compared to water scarcity approaches based on water quantity only, particularly at local scales. Further, our results from the Central Valley region highlights that severe water scarcity can be strongly alleviated by conjunctive groundwater use, to dilute and lower salinity levels below crop specific tolerance values in many sub-basins. However, groundwater resources needed for dilution frequently exceed renewable groundwater rates in this region, posing additional risks for groundwater depletion. Taken together, through capturing these dynamics, our water scarcity framework can support local-regional water management and provide a useful tool for sustainable water use and assessing the impact of agricultural practices, such as crop choices, on water scarcity levels.