Dietary changes could compensate for potential yield reductions upon global river flow protection

Non-technical Summary Globally, freshwater systems are degrading due to excessive water withdrawals. We estimate that if rivers' environmental flow requirements were protected, the associated decrease in irrigation water availability would reduce global yields by ~5%. As one option to increase food supply within limited water resources, we show that dietary changes towards less livestock products could compensate for this effect. If all currently grown edible feed was directly consumed by humans, we estimate that global food supply would even increase by 19%. We thus provide evidence that dietary changes are an important strategy to harmonize river flow protection with sustained food supply. Technical Summary To protect global freshwater ecosystems and restore their integrity, freshwater withdrawals could be restricted to maintain rivers' environmental flow requirements (EFRs). However, without further measures, reduced irrigation water availability would decrease crop yields and put additional pressure on global food provision. By comparing the quantitative effects of both global EFR protection and dietary changes on regional and global food supply in a spatially explicit modelling framework, we show that dietary changes towards less livestock products could effectively contribute to solving this trade-off. Results indicate that protection of EFRs would almost halve current global irrigation water withdrawals and reduce global crop yields by 5%. Limiting animal protein share to 25%, 12.5% and 0% of total protein supply and shifting released crop feed to direct human consumption could however increase global food supply by 4%, 11% and 19%, respectively. The effects are geographically decoupled: Water-scarce regions such as the Middle East, or South and Central Asia would be most affected by EFR protection, whereas dietary changes are most effective in North America and Europe. This underpins the disproportionally high responsibilities of countries with resource-intensive diets and the need for regionally adapted and diverse strategies to transform the global food system towards sustainability. Social Media Summary Combining dietary changes and global river flow protection could contribute to a more sustainable food system.