Intensification and Spatial Reorganization of Drought Risks for Global Rainfed Crops Under Climate Change

Rainfed agriculture covers roughly 80% of global cropland and supplies more than half of global food production, yet uncertainty in how meteorological drying propagates into root-zone water deficits and crop losses impedes robust risk assessment. Here, we establish an integrated, production-weighted assessment framework coupling SPEI, SSI, and 12 GGCMI3 crop models to trace how meteorological drying propagates into root-zone deficits and crop losses, explicitly separating affected area, conditional yield loss, and accumulated production loss across rainfed maize, soybean, and wheat. By 2070-2099, opposing-direction SPEI-SSI change classes occupied 6.8%-28.4% of rainfed area across crops under SSP1-2.6/default CO₂ and 26.6%-48.2% under SSP5-8.5/default CO₂. Comparison with fixed-2015 CO₂ experiments (7.5%-27.6% and 21.7%-34.9%, respectively) indicates that elevated CO₂ substantially expanded the spatial footprint of this hydrometeorological decoupling. Historically, SSI-defined drought affected 12-16 million ha year^-1 and was associated with annual production losses of 5-12 Mt year^-1 (1.6-2.0% year^-1). Under default CO₂, affected area increased to 14-21 million ha under SSP1-2.6 and 19-27 million ha under SSP5-8.5, with production losses of 6-12 and 9-12 Mt year^-1, respectively. Under SSP5-8.5, median loss rates were higher under fixed-2015 than default CO₂ for maize (3.33 vs. 1.96% year^-1), soybean (4.22 vs. 2.84% year^-1) and wheat (5.41 vs. 2.90% year^-1), as elevated CO₂ reduces stomatal water loss and thus mitigates drought impacts, whereas SSP1-2.6 estimates were similar. Severe drought became the largest loss contributor under both pathways and CO₂ settings. Under default CO₂, loss increases clustered in Central America, northeastern Brazil, western Europe and southern Africa; fixed-2015 CO₂ broadened the area of robust grid-cell loss increases. These results show that drought-related production losses are spatially uneven and sensitive to the modeled CO₂ response, highlighting the value of crop- and region-specific risk assessment.