Salinity impacts on irrigation water-scarcity in food bowl regions of the US and Australia

Abstract

Irrigation water use and crop production may be severely limited by both water shortages and increased salinity levels. However, impacts of crop-specific salinity limitations on irrigation water scarcity are largely unknown. We develop a salinity-inclusive water scarcity framework for the irrigation sector, accounting for crop-specific irrigation water demands and salinity tolerance levels and apply it to 29 sub-basins within two food bowl regions; the Central Valley (California) and the Murray Darling Basin (Australia). Our results show that severe water scarcity (levels >0.4) occurs in 23 % and 66 % of all instances (from > 17,000 monthly crop-specific estimates) for the Central Valley and Murray Darling Basin, respectively. The highest water scarcity levels for both regions occurred during their summer seasons. Including salinity and crop-specific salinity tolerance levels further increased water scarcity levels, compared to estimations based on water quantity only, particularly at local sub-basin scales. We further investigate the potential of alleviating water scarcity through diluting surface water with lower saline groundwater resources, at instances where crop salinity tolerance levels are exceeded (conjunctive water use). Results from the Central Valley highlights that conjunctive water use can reduce severe water scarcity levels by up to 67 % (from 946 monthly instances where surface water salinity tolerance levels were exceeded). However, groundwater dilution requirements frequently exceed renewable groundwater rates, posing additional risks for groundwater depletion in several sub-basins. By capturing the dynamics of both crops, salinity and conjunctive water use, our framework can support local-regional agricultural and water management impacts, on water scarcity levels.

DynQual v1.0: a high-resolution global surface water quality model

“…The newly developed DynQual model builds on the modelling framework of DynWat, a global water temperature model that solves the energy-water balance to simulate daily water temperature (T w ) and ice thickness (Van Beek et al, 2012;Wanders et al, 2019). A full model description including the energy balance equations and the representation of ice cover, floodplains, channel roughness and lakes and reservoirs within DynWat is available in published literature (Wanders et al, 2019).…”

“…Water temperature (T w ) is simulated by solving the surface water energy balance using the DynWat model as basis (Van Beek et al, 2012;Wanders et al, 2019). In addition to solving the surface water energy balance, DynWat also accounts for surface water abstraction, reservoirs, riverine flooding and the formation of ice (Wanders et al, 2019).…”

“…Another example is salinization of water resources, which can both limit irrigation water use (Thorslund et al, 2022) and threaten freshwater biodiversity (Velasco et al, 2019) where species cannot tolerate elevated salinity concentrations. Similarly, increased water temperatures can disrupt energy production ( Van Vliet et al, 2016), and also provide more favourable conditions for cyanobacterial blooms that can lead to hypoxia, which can disrupt freshwater habitats (Smucker et al, 2021).…”

“…Both of these factors increase river water contamination, threatening both the safe usability of water and environmental health. Climate change is also altering the thermal regime of rivers ( Van Vliet et al, 2013), with higher temperatures also causing dissolved oxygen depletion (Ozaki et al, 2003).…”

“…More directly, sectoral activities generate return flows: water that is extracted for a specific purpose but is not consumed (evaporated) in the process but which has changed in composition as a result of the water use activity (Sutanudjaja et al, 2018;Jones et al, 2021). For example, the composition of domestic wastewater will reflect the various household water uses, including organic and fecal contamination from human waste (WWAP, 2017) and elevated nutrient concentrations from household chemicals and laundry detergents (Van Puijenbroek et al, 2019). The reintroduction of these flows back to the environment represents a significant source of pollutant loadings that degrade river water quality (Jones et al, 2022a).…”