Current Models Underestimate Future Irrigated Areas

Predictions of global irrigated areas are widely used to guide strategies that aim to secure environmental welfare and manage climate change. Here we show that these predictions, which range between 240 and 450 million hectares (Mha), underestimate the potential extension of irrigation by ignoring basic parametric and model uncertainties. We found that the probability distribution of global irrigated areas in 2050 spans almost half an order of magnitude (similar to 300-800 Mha, P-2.5,P-97.5), with the right tail pushing values to up to similar to 1,800 Mha. This uncertainty is mostly irreducible as it is largely caused by either population-related parameters or the assumptions behind the model design. Model end-users and policy makers should acknowledge that irrigated areas are likely to grow much more than previously thought in order to avoid underestimating potential environmental costs.